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Zir.zig

Zig Intermediate Representation.

Astgen.zig converts AST nodes to these untyped IR instructions. Next, Sema.zig processes these into AIR. The minimum amount of information needed to represent a list of ZIR instructions. Once this structure is completed, it can be used to generate AIR, followed by machine code, without any memory access into the AST tree token list, node list, or source bytes. Exceptions include:

File

Code

//! Zig Intermediate Representation.
//!
//! Astgen.zig converts AST nodes to these untyped IR instructions. Next,
//! Sema.zig processes these into AIR.
//! The minimum amount of information needed to represent a list of ZIR instructions.
//! Once this structure is completed, it can be used to generate AIR, followed by
//! machine code, without any memory access into the AST tree token list, node list,
//! or source bytes. Exceptions include:
//!  * Compile errors, which may need to reach into these data structures to
//!    create a useful report.
//!  * In the future, possibly inline assembly, which needs to get parsed and
//!    handled by the codegen backend, and errors reported there. However for now,
//!    inline assembly is not an exception.
const Zir = @This();
const builtin = @import("builtin");

const std = @import("std");
const Io = std.Io;
const mem = std.mem;
const Allocator = std.mem.Allocator;
const assert = std.debug.assert;
const BigIntConst = std.math.big.int.Const;
const BigIntMutable = std.math.big.int.Mutable;
const Ast = std.zig.Ast;

instructions: std.MultiArrayList(Inst).Slice,
/// In order to store references to strings in fewer bytes, we copy all
/// string bytes into here. String bytes can be null. It is up to whomever
/// is referencing the data here whether they want to store both index and length,
/// thus allowing null bytes, or store only index, and use null-termination. The
/// `string_bytes` array is agnostic to either usage.
/// Index 0 is reserved for special cases.
string_bytes: []u8,
/// The meaning of this data is determined by `Inst.Tag` value.
/// The first few indexes are reserved. See `ExtraIndex` for the values.
extra: []u32,

/// The data stored at byte offset 0 when ZIR is stored in a file.
pub const Header = extern struct {
    instructions_len: u32,
    string_bytes_len: u32,
    extra_len: u32,
    /// We could leave this as padding, however it triggers a Valgrind warning because
    /// we read and write undefined bytes to the file system. This is harmless, but
    /// it's essentially free to have a zero field here and makes the warning go away,
    /// making it more likely that following Valgrind warnings will be taken seriously.
    unused: u32 = 0,
    stat_inode: Io.File.INode,
    stat_size: u64,
    stat_mtime: i128,
};

pub const ExtraIndex = enum(u32) {
    /// If this is 0, no compile errors. Otherwise there is a `CompileErrors`
    /// payload at this index.
    compile_errors,
    /// If this is 0, this file contains no imports. Otherwise there is a `Imports`
    /// payload at this index.
    imports,

    _,
};

fn ExtraData(comptime T: type) type {
    return struct { data: T, end: usize };
}

/// Returns the requested data, as well as the new index which is at the start of the
/// trailers for the object.
pub fn extraData(code: Zir, comptime T: type, index: usize) ExtraData(T) {
    const info = @typeInfo(T).@"struct";
    var i: usize = index;
    var result: T = undefined;
    inline for (info.field_names, info.field_types) |field_name, field_type| {
        @field(result, field_name) = switch (field_type) {
            u32 => code.extra[i],

            Inst.Ref,
            Inst.Index,
            Inst.Declaration.Name,
            std.zig.SimpleComptimeReason,
            NullTerminatedString,
            // Ast.TokenIndex is missing because it is a u32.
            Ast.OptionalTokenIndex,
            Ast.Node.Index,
            Ast.Node.OptionalIndex,
            => @fromBackingInt(@intCast(code.extra[i])),

            Ast.TokenOffset,
            Ast.OptionalTokenOffset,
            Ast.Node.Offset,
            Ast.Node.OptionalOffset,
            => @fromBackingInt(@intCast(@as(i32, @bitCast(code.extra[i])))),

            Inst.Call.Flags,
            Inst.BuiltinCall.Flags,
            Inst.SwitchBlock.Bits,
            Inst.FuncFancy.Bits,
            Inst.Declaration.Flags,
            Inst.Param.Type,
            Inst.Func.RetTy,
            => @bitCast(code.extra[i]),

            else => @compileError("bad field type"),
        };
        i += 1;
    }
    return .{
        .data = result,
        .end = i,
    };
}

pub const NullTerminatedString = enum(u32) {
    empty = 0,
    _,
};

/// Given an index into `string_bytes` returns the null-terminated string found there.
pub fn nullTerminatedString(code: Zir, index: NullTerminatedString) [:0]const u8 {
    const slice = code.string_bytes[@backingInt(index)..];
    return slice[0..std.mem.findScalar(u8, slice, 0).? :0];
}

pub fn refSlice(code: Zir, start: usize, len: usize) []Inst.Ref {
    return @ptrCast(code.extra[start..][0..len]);
}

pub fn bodySlice(zir: Zir, start: usize, len: usize) []Inst.Index {
    return @ptrCast(zir.extra[start..][0..len]);
}

pub fn hasCompileErrors(code: Zir) bool {
    if (code.extra[@backingInt(ExtraIndex.compile_errors)] != 0) {
        return true;
    } else {
        assert(code.instructions.len != 0); // i.e. lowering did not fail
        return false;
    }
}

pub fn loweringFailed(code: Zir) bool {
    if (code.instructions.len == 0) {
        assert(code.hasCompileErrors());
        return true;
    } else {
        return false;
    }
}

pub fn deinit(code: *Zir, gpa: Allocator) void {
    code.instructions.deinit(gpa);
    gpa.free(code.string_bytes);
    gpa.free(code.extra);
    code.* = undefined;
}

/// These are untyped instructions generated from an Abstract Syntax Tree.
/// The data here is immutable because it is possible to have multiple
/// analyses on the same ZIR happening at the same time.
pub const Inst = struct {
    tag: Tag,
    data: Data,

    /// These names are used directly as the instruction names in the text format.
    /// See `data_field_map` for a list of which `Data` fields are used by each `Tag`.
    pub const Tag = enum(u8) {
        /// Arithmetic addition, asserts no integer overflow.
        /// Uses the `pl_node` union field. Payload is `Bin`.
        add,
        /// Twos complement wrapping integer addition.
        /// Uses the `pl_node` union field. Payload is `Bin`.
        addwrap,
        /// Saturating addition.
        /// Uses the `pl_node` union field. Payload is `Bin`.
        add_sat,
        /// The same as `add` except no safety check.
        add_unsafe,
        /// Arithmetic subtraction. Asserts no integer overflow.
        /// Uses the `pl_node` union field. Payload is `Bin`.
        sub,
        /// Twos complement wrapping integer subtraction.
        /// Uses the `pl_node` union field. Payload is `Bin`.
        subwrap,
        /// Saturating subtraction.
        /// Uses the `pl_node` union field. Payload is `Bin`.
        sub_sat,
        /// Arithmetic multiplication. Asserts no integer overflow.
        /// Uses the `pl_node` union field. Payload is `Bin`.
        mul,
        /// Twos complement wrapping integer multiplication.
        /// Uses the `pl_node` union field. Payload is `Bin`.
        mulwrap,
        /// Saturating multiplication.
        /// Uses the `pl_node` union field. Payload is `Bin`.
        mul_sat,
        /// Implements the `@divExact` builtin.
        /// Uses the `pl_node` union field with payload `Bin`.
        div_exact,
        /// Implements the `@divFloor` builtin.
        /// Uses the `pl_node` union field with payload `Bin`.
        div_floor,
        /// Implements the `@divCeil` builtin.
        /// Uses the `pl_node` union field with payload `Bin`.
        div_ceil,
        /// Implements the `@divTrunc` builtin.
        /// Uses the `pl_node` union field with payload `Bin`.
        div_trunc,
        /// Implements the `@mod` builtin.
        /// Uses the `pl_node` union field with payload `Bin`.
        mod,
        /// Implements the `@rem` builtin.
        /// Uses the `pl_node` union field with payload `Bin`.
        rem,
        /// Ambiguously remainder division or modulus. If the computation would possibly have
        /// a different value depending on whether the operation is remainder division or modulus,
        /// a compile error is emitted. Otherwise the computation is performed.
        /// Uses the `pl_node` union field. Payload is `Bin`.
        mod_rem,
        /// Integer shift-left. Zeroes are shifted in from the right hand side.
        /// Uses the `pl_node` union field. Payload is `Bin`.
        shl,
        /// Implements the `@shlExact` builtin.
        /// Uses the `pl_node` union field with payload `Bin`.
        shl_exact,
        /// Saturating shift-left.
        /// Uses the `pl_node` union field. Payload is `Bin`.
        shl_sat,
        /// Integer shift-right. Arithmetic or logical depending on the signedness of
        /// the integer type.
        /// Uses the `pl_node` union field. Payload is `Bin`.
        shr,
        /// Implements the `@shrExact` builtin.
        /// Uses the `pl_node` union field with payload `Bin`.
        shr_exact,

        /// Declares a parameter of the current function. Used for:
        /// * debug info
        /// * checking shadowing against declarations in the current namespace
        /// * parameter type expressions referencing other parameters
        /// These occur in the block outside a function body (the same block as
        /// contains the func instruction).
        /// Uses the `pl_tok` field. Token is the parameter name, payload is a `Param`.
        param,
        /// Same as `param` except the parameter is marked comptime.
        param_comptime,
        /// Same as `param` except the parameter is marked anytype.
        /// Uses the `str_tok` field. Token is the parameter name. String is the parameter name.
        param_anytype,
        /// Same as `param` except the parameter is marked both comptime and anytype.
        /// Uses the `str_tok` field. Token is the parameter name. String is the parameter name.
        param_anytype_comptime,
        /// Array concatenation. `a ++ b`
        /// Uses the `pl_node` union field. Payload is `Bin`.
        array_cat,
        /// `[N]T` syntax. No source location provided.
        /// Uses the `pl_node` union field. Payload is `Bin`. lhs is length, rhs is element type.
        array_type,
        /// `[N:S]T` syntax. Source location is the array type expression node.
        /// Uses the `pl_node` union field. Payload is `ArrayTypeSentinel`.
        array_type_sentinel,
        /// `@Int` builtin.
        /// Uses the `pl_node` union field with `Bin` payload.
        /// lhs is signedness, rhs is bit count.
        reify_int,
        /// `@Vector` builtin.
        /// Uses the `pl_node` union field with `Bin` payload.
        /// lhs is length, rhs is element type.
        vector_type,
        /// Given a pointer type, returns its element type. Reaches through any optional or error
        /// union types wrapping the pointer. Asserts that the underlying type is a pointer type.
        /// Returns generic poison if the element type is `anyopaque`.
        /// Uses the `un_node` field.
        elem_type,
        /// Given an indexable pointer (slice, many-ptr, single-ptr-to-array), returns its
        /// element type. Emits a compile error if the type is not an indexable pointer.
        /// Uses the `un_node` field.
        indexable_ptr_elem_type,
        /// Given a vector or array type, strips off any error unions or
        /// optionals layered on top and returns its element type.
        ///
        /// `!?[N]T` -> `T`
        ///
        /// Uses the `un_node` field.
        splat_op_result_ty,
        /// Given a type, strips away any error unions or optionals stacked
        /// on top, validates it for usage with `@fromBackingInt` and returns
        /// its backing integer type.
        ///
        /// `E!?enum(T) { _ }` -> `T`
        ///
        /// Uses the `un_node` field.
        from_backing_int_arg_ty,
        /// Given a pointer to an indexable object, returns the len property. This is
        /// used by for loops. This instruction also emits a for-loop specific compile
        /// error if the indexable object is not indexable.
        /// Uses the `un_node` field. The AST node is the for loop node.
        indexable_ptr_len,
        /// Create a `anyframe->T` type.
        /// Uses the `un_node` field.
        anyframe_type,
        /// Type coercion to the function's return type.
        /// Uses the `pl_node` field. Payload is `As`. AST node could be many things.
        as_node,
        /// Same as `as_node` but ignores runtime to comptime int error.
        as_shift_operand,
        /// Bitwise AND. `&`
        bit_and,
        /// Reinterpret the memory representation of a value as a different type.
        /// Uses the pl_node field with payload `Bin`.
        bitcast,
        /// Bitwise NOT. `~`
        /// Uses `un_node`.
        bit_not,
        /// Bitwise OR. `|`
        bit_or,
        /// A labeled block of code, which can return a value.
        /// Uses the `pl_node` union field. Payload is `Block`.
        block,
        /// Like `block`, but forces full evaluation of its contents at compile-time.
        /// Exited with `break_inline`.
        /// Uses the `pl_node` union field. Payload is `BlockComptime`.
        block_comptime,
        /// A list of instructions which are analyzed in the parent context, without
        /// generating a runtime block. Must terminate with an "inline" variant of
        /// a noreturn instruction.
        /// Uses the `pl_node` union field. Payload is `Block`.
        block_inline,
        /// This instruction may only ever appear in the list of declarations for a
        /// namespace type, e.g. within a `struct_decl` instruction. It represents a
        /// single source declaration (`const`/`var`/`fn`), containing the name,
        /// attributes, type, and value of the declaration.
        /// Uses the `declaration` union field. Payload is `Declaration`.
        declaration,
        /// Implements `suspend {...}`.
        /// Uses the `pl_node` union field. Payload is `Block`.
        suspend_block,
        /// Boolean NOT. See also `bit_not`.
        /// Uses the `un_node` field.
        bool_not,
        /// Short-circuiting boolean `and`. `lhs` is a boolean `Ref` and the other operand
        /// is a block, which is evaluated if `lhs` is `true`.
        /// Uses the `pl_node` union field. Payload is `BoolBr`.
        bool_br_and,
        /// Short-circuiting boolean `or`. `lhs` is a boolean `Ref` and the other operand
        /// is a block, which is evaluated if `lhs` is `false`.
        /// Uses the `pl_node` union field. Payload is `BoolBr`.
        bool_br_or,
        /// Return a value from a block.
        /// Uses the `break` union field.
        /// Uses the source information from previous instruction.
        @"break",
        /// Return a value from a block. This instruction is used as the terminator
        /// of a `block_inline`. It allows using the return value from `Sema.analyzeBody`.
        /// This instruction may also be used when it is known that there is only one
        /// break instruction in a block, and the target block is the parent.
        /// Uses the `break` union field.
        break_inline,
        /// Branch from within a switch case to the case specified by the operand.
        /// Uses the `break` union field. `block_inst` refers to a `switch_block`/
        /// `switch_block_ref`/`switch_block_err_union`.
        switch_continue,
        /// Checks that comptime control flow does not happen inside a runtime block.
        /// Uses the `un_node` union field.
        check_comptime_control_flow,
        /// Function call.
        /// Uses the `pl_node` union field with payload `Call`.
        /// AST node is the function call.
        call,
        /// Function call using `a.b()` syntax.
        /// Uses the named field as the callee. If there is no such field, searches in the type for
        /// a decl matching the field name. The decl is resolved and we ensure that it's a function
        /// which can accept the object as the first parameter, with one pointer fixup. This
        /// function is then used as the callee, with the object as an implicit first parameter.
        /// Uses the `pl_node` union field with payload `FieldCall`.
        /// AST node is the function call.
        field_call,
        /// Implements the `@call` builtin.
        /// Uses the `pl_node` union field with payload `BuiltinCall`.
        /// AST node is the builtin call.
        builtin_call,
        /// `<`
        /// Uses the `pl_node` union field. Payload is `Bin`.
        cmp_lt,
        /// `<=`
        /// Uses the `pl_node` union field. Payload is `Bin`.
        cmp_lte,
        /// `==`
        /// Uses the `pl_node` union field. Payload is `Bin`.
        cmp_eq,
        /// `>=`
        /// Uses the `pl_node` union field. Payload is `Bin`.
        cmp_gte,
        /// `>`
        /// Uses the `pl_node` union field. Payload is `Bin`.
        cmp_gt,
        /// `!=`
        /// Uses the `pl_node` union field. Payload is `Bin`.
        cmp_neq,
        /// Conditional branch. Splits control flow based on a boolean condition value.
        /// Uses the `pl_node` union field. AST node is an if, while, for, etc.
        /// Payload is `CondBr`.
        condbr,
        /// Same as `condbr`, except the condition is coerced to a comptime value, and
        /// only the taken branch is analyzed. The then block and else block must
        /// terminate with an "inline" variant of a noreturn instruction.
        condbr_inline,
        /// Given an operand which is an error union, splits control flow. In
        /// case of error, control flow goes into the block that is part of this
        /// instruction, which is guaranteed to end with a return instruction
        /// and never breaks out of the block.
        /// In the case of non-error, control flow proceeds to the next instruction
        /// after the `try`, with the result of this instruction being the unwrapped
        /// payload value, as if `err_union_payload_unsafe` was executed on the operand.
        /// Uses the `pl_node` union field. Payload is `Try`.
        @"try",
        /// Same as `try` except the operand is a pointer and the result is a pointer.
        try_ptr,
        /// An error set type definition. Contains a list of field names.
        /// Uses the `pl_node` union field. Payload is `ErrorSetDecl`.
        error_set_decl,
        /// Declares the beginning of a statement. Used for debug info.
        /// Uses the `dbg_stmt` union field. The line and column are offset
        /// from the parent declaration.
        dbg_stmt,
        /// Marks a variable declaration. Used for debug info.
        /// Uses the `str_op` union field. The string is the local variable name,
        /// and the operand is the pointer to the variable's location. The local
        /// may be a const or a var.
        dbg_var_ptr,
        /// Same as `dbg_var_ptr` but the local is always a const and the operand
        /// is the local's value.
        dbg_var_val,
        /// Uses a name to identify a Decl and takes a pointer to it.
        ///
        /// Uses the `str_tok` union field.
        decl_ref,
        /// Uses a name to identify a Decl and uses it as a value.
        /// Uses the `str_tok` union field.
        decl_val,
        /// Load the value from a pointer. Assumes `x.*` syntax.
        /// Uses `un_node` field. AST node is the `x.*` syntax.
        load,
        /// Arithmetic division. Asserts no integer overflow.
        /// Uses the `pl_node` union field. Payload is `Bin`.
        div,
        /// Given a pointer to an array, slice, or pointer, returns a pointer to the element at
        /// the provided index.
        /// Uses the `pl_node` union field. AST node is a[b] syntax. Payload is `Bin`.
        elem_ptr_node,
        /// Same as `elem_ptr_node` but used only for for loop.
        /// Uses the `pl_node` union field. AST node is the condition of a for loop.
        /// Payload is `Bin`.
        /// No OOB safety check is emitted.
        elem_ptr,
        /// Given a pointer to an array, slice, or pointer, loads the element
        /// at the provided index.
        ///
        /// Uses the `pl_node` union field. AST node is a[b] syntax. Payload is `Bin`.
        elem_ptr_load,
        /// Given an array, slice, or pointer, returns the element at the
        /// provided index.
        ///
        /// Uses the `pl_node` union field. AST node is the condition of a for
        /// loop. Payload is `Bin`.
        ///
        /// No OOB safety check is emitted.
        elem_val,
        /// Same as `elem_val` but takes the index as an immediate value.
        /// No OOB safety check is emitted. A prior instruction must validate this operation.
        /// Uses the `elem_val_imm` union field.
        elem_val_imm,
        /// Emits a compile error if the operand is not `void`.
        /// Uses the `un_node` field.
        ensure_result_used,
        /// Emits a compile error if an error is ignored.
        /// Uses the `un_node` field.
        ensure_result_non_error,
        /// Emits a compile error error union payload is not void.
        ensure_err_union_payload_void,
        /// Create a `E!T` type.
        /// Uses the `pl_node` field with `Bin` payload.
        error_union_type,
        /// `error.Foo` syntax. Uses the `str_tok` field of the Data union.
        error_value,
        /// Implements the `@export` builtin function.
        /// Uses the `pl_node` union field. Payload is `Export`.
        @"export",
        /// Given a pointer to a struct or object that contains virtual fields, returns a pointer
        /// to the named field. The field name is stored in string_bytes. Used by a.b syntax.
        /// Uses `pl_node` field. The AST node is the a.b syntax. Payload is Field.
        field_ptr,
        /// Given a pointer to a struct or object that contains virtual fields, loads from the
        /// named field.
        ///
        /// The field name is stored in string_bytes. Used by a.b syntax.
        ///
        /// This instruction also accepts a pointer.
        ///
        /// Uses `pl_node` field. The AST node is the a.b syntax. Payload is Field.
        field_ptr_load,
        /// Given a pointer to a struct or object that contains virtual fields, returns a pointer
        /// to the named field. The field name is a comptime instruction. Used by @field.
        /// Uses `pl_node` field. The AST node is the builtin call. Payload is FieldNamed.
        field_ptr_named,
        /// Given a pointer to a struct or object that contains virtual fields,
        /// loads from the named field.
        ///
        /// The field name is a comptime instruction. Used by @field.
        ///
        /// Uses `pl_node` field. The AST node is the builtin call. Payload is FieldNamed.
        field_ptr_named_load,
        /// Returns a function type, or a function instance, depending on whether
        /// the body_len is 0. Calling convention is auto.
        /// Uses the `pl_node` union field. `payload_index` points to a `Func`.
        func,
        /// Same as `func` but has an inferred error set.
        func_inferred,
        /// Represents a function declaration or function prototype, depending on
        /// whether body_len is 0.
        /// Uses the `pl_node` union field. `payload_index` points to a `FuncFancy`.
        func_fancy,
        /// Implements the `@import` builtin.
        /// Uses the `pl_tok` field.
        import,
        /// Integer literal that fits in a u64. Uses the `int` union field.
        int,
        /// Arbitrary sized integer literal. Uses the `str` union field.
        int_big,
        /// A float literal that fits in a f64. Uses the float union value.
        float,
        /// A float literal that fits in a f128. Uses the `pl_node` union value.
        /// Payload is `Float128`.
        float128,
        /// Make an integer type out of signedness and bit count.
        /// Payload is `int_type`
        int_type,
        /// Return a boolean false if an optional is null. `x != null`
        /// Uses the `un_node` field.
        is_non_null,
        /// Return a boolean false if an optional is null. `x.* != null`
        /// Uses the `un_node` field.
        is_non_null_ptr,
        /// Return a boolean false if value is an error
        /// Uses the `un_node` field.
        is_non_err,
        /// Return a boolean false if dereferenced pointer is an error
        /// Uses the `un_node` field.
        is_non_err_ptr,
        /// Same as `is_non_er` but doesn't validate that the type can be an error.
        /// Uses the `un_node` field.
        ret_is_non_err,
        /// A labeled block of code that loops forever. At the end of the body will have either
        /// a `repeat` instruction or a `repeat_inline` instruction.
        /// Uses the `pl_node` field. The AST node is either a for loop or while loop.
        /// This ZIR instruction is needed because AIR does not (yet?) match ZIR, and Sema
        /// needs to emit more than 1 AIR block for this instruction.
        /// The payload is `Block`.
        loop,
        /// Sends runtime control flow back to the beginning of the current block.
        /// Uses the `node` field.
        repeat,
        /// Sends comptime control flow back to the beginning of the current block.
        /// Uses the `node` field.
        repeat_inline,
        /// Asserts that all the lengths provided match. Used to build a for loop.
        /// Return value is the length as a usize.
        /// Uses the `pl_node` field with payload `MultiOp`.
        /// There are two items for each AST node inside the for loop condition.
        /// If both items in a pair are `.none`, then this node is an unbounded range.
        /// If only the second item in a pair is `.none`, then the first is an indexable.
        /// Otherwise, the node is a bounded range `a..b`, with the items being `a` and `b`.
        /// Illegal behaviors:
        ///  * If all lengths are unbounded ranges (always a compile error).
        ///  * If any two lengths do not match each other.
        for_len,
        /// Merge two error sets into one, `E1 || E2`.
        /// Uses the `pl_node` field with payload `Bin`.
        merge_error_sets,
        /// Turns an R-Value into a const L-Value. In other words, it takes a value,
        /// stores it in a memory location, and returns a const single-item pointer to it.
        /// If the value is `comptime`, the memory location is global static constant data.
        /// Otherwise, the memory location is in the stack frame, local to the scope
        /// containing the instruction.
        /// Uses the `un_tok` union field.
        ref,
        /// Implements the dereference operand (`.*`). Checks that operand is a pointer
        /// that supports being directly dereferenced.
        /// Uses the `un_node` union field.
        deref,
        /// Emitted when a dereference (`.*`) with a reference result location occurs.
        /// Checks that operand is a pointer that supports being directly dereferenced
        /// and returns a single-item pointer to the dereferenced memory location.
        /// Uses the `un_node` union field.
        ref_deref,
        /// Sends control flow back to the function's callee.
        /// Includes an operand as the return value.
        /// Includes an AST node source location.
        /// Uses the `un_node` union field.
        ret_node,
        /// Sends control flow back to the function's callee.
        /// The operand is a `ret_ptr` instruction, where the return value can be found.
        /// Includes an AST node source location.
        /// Uses the `un_node` union field.
        ret_load,
        /// Sends control flow back to the function's callee.
        /// Includes an operand as the return value.
        /// Includes a token source location.
        /// Uses the `un_tok` union field.
        ret_implicit,
        /// Sends control flow back to the function's callee.
        /// The return operand is `error.foo` where `foo` is given by the string.
        /// If the current function has an inferred error set, the error given by the
        /// name is added to it.
        /// Uses the `str_tok` union field.
        ret_err_value,
        /// Obtains a pointer to the return value.
        /// Uses the `node` union field.
        ret_ptr,
        /// Obtains the return type of the in-scope function.
        /// Uses the `node` union field.
        ret_type,
        /// Create a pointer type which can have a sentinel, alignment, address space, and/or bit range.
        /// Uses the `ptr_type` union field.
        ptr_type,
        /// Slice operation `lhs[rhs..]`. No sentinel and no end offset.
        /// Returns a pointer to the subslice.
        /// Uses the `pl_node` field. AST node is the slice syntax. Payload is `SliceStart`.
        slice_start,
        /// Slice operation `array_ptr[start..end]`. No sentinel.
        /// Returns a pointer to the subslice.
        /// Uses the `pl_node` field. AST node is the slice syntax. Payload is `SliceEnd`.
        slice_end,
        /// Slice operation `array_ptr[start..end:sentinel]`.
        /// Returns a pointer to the subslice.
        /// Uses the `pl_node` field. AST node is the slice syntax. Payload is `SliceSentinel`.
        slice_sentinel,
        /// Slice operation `array_ptr[start..][0..len]`. Optional sentinel.
        /// Returns a pointer to the subslice.
        /// Uses the `pl_node` field. AST node is the slice syntax. Payload is `SliceLength`.
        slice_length,
        /// Given a value which is a pointer to the LHS of a slice operation, return the sentinel
        /// type, used as the result type of the slice sentinel (i.e. `s` in `lhs[a..b :s]`).
        /// Uses the `un_node` field. AST node is the slice syntax. Operand is `lhs`.
        slice_sentinel_ty,
        /// Same as `store` except provides a source location.
        /// Uses the `pl_node` union field. Payload is `Bin`.
        store_node,
        /// Same as `store_node` but the type of the value being stored will be
        /// used to infer the pointer type of an `alloc_inferred`.
        /// Uses the `pl_node` union field. Payload is `Bin`.
        store_to_inferred_ptr,
        /// String Literal. Makes an anonymous Decl and then takes a pointer to it.
        /// Uses the `str` union field.
        str,
        /// Arithmetic negation. Asserts no integer overflow.
        /// Same as sub with a lhs of 0, split into a separate instruction to save memory.
        /// Uses `un_node`.
        negate,
        /// Twos complement wrapping integer negation.
        /// Same as subwrap with a lhs of 0, split into a separate instruction to save memory.
        /// Uses `un_node`.
        negate_wrap,
        /// Returns the type of a value.
        /// Uses the `un_node` field.
        typeof,
        /// Implements `@TypeOf` for one operand.
        /// Uses the `pl_node` field. Payload is `Block`.
        typeof_builtin,
        /// Given a value, look at the type of it, which must be an integer type.
        /// Returns the integer type for the RHS of a shift operation.
        /// Uses the `un_node` field.
        typeof_log2_int_type,
        /// Asserts control-flow will not reach this instruction (`unreachable`).
        /// Uses the `@"unreachable"` union field.
        @"unreachable",
        /// Bitwise XOR. `^`
        /// Uses the `pl_node` union field. Payload is `Bin`.
        xor,
        /// Create an optional type '?T'
        /// Uses the `un_node` field.
        optional_type,
        /// ?T => T with safety.
        /// Given an optional value, returns the payload value, with a safety check that
        /// the value is non-null. Used for `orelse`, `if` and `while`.
        /// Uses the `un_node` field.
        optional_payload_safe,
        /// ?T => T without safety.
        /// Given an optional value, returns the payload value. No safety checks.
        /// Uses the `un_node` field.
        optional_payload_unsafe,
        /// *?T => *T with safety.
        /// Given a pointer to an optional value, returns a pointer to the payload value,
        /// with a safety check that the value is non-null. Used for `orelse`, `if` and `while`.
        /// Uses the `un_node` field.
        optional_payload_safe_ptr,
        /// *?T => *T without safety.
        /// Given a pointer to an optional value, returns a pointer to the payload value.
        /// No safety checks.
        /// Uses the `un_node` field.
        optional_payload_unsafe_ptr,
        /// E!T => T without safety.
        /// Given an error union value, returns the payload value. No safety checks.
        /// Uses the `un_node` field.
        err_union_payload_unsafe,
        /// *E!T => *T without safety.
        /// Given a pointer to a error union value, returns a pointer to the payload value.
        /// No safety checks.
        /// Uses the `un_node` field.
        err_union_payload_unsafe_ptr,
        /// E!T => E without safety.
        /// Given an error union value, returns the error code. No safety checks.
        /// Uses the `un_node` field.
        err_union_code,
        /// *E!T => E without safety.
        /// Given a pointer to an error union value, returns the error code. No safety checks.
        /// Uses the `un_node` field.
        err_union_code_ptr,
        /// An enum literal. Uses the `str_tok` union field.
        enum_literal,
        /// A decl literal. This is similar to `field`, but unwraps error unions and optionals,
        /// and coerces the result to the given type.
        /// Uses the `pl_node` union field. Payload is `Field`.
        decl_literal,
        /// The same as `decl_literal`, but the coercion is omitted. This is used for decl literal
        /// function call syntax, i.e. `.foo()`.
        /// Uses the `pl_node` union field. Payload is `Field`.
        decl_literal_no_coerce,
        /// A switch expression. Uses the `pl_node` union field.
        /// AST node is the switch, payload is `SwitchBlock`.
        switch_block,
        /// A switch expression. Uses the `pl_node` union field.
        /// AST node is the switch, payload is `SwitchBlock`. Operand is a pointer.
        switch_block_ref,
        /// A switch on an error union:
        /// - `eu catch |err| switch (err) {...}`, AST node is the `catch`.
        /// - `if (eu) |payload| {...} else |err| {...}`, AST node is the `if`.
        /// Uses the `pl_node` union field. Payload is `SwitchBlock`.
        switch_block_err_union,
        /// Check that the operand's type is an array or tuple with the given number of elements.
        /// Uses the `pl_node` field. Payload is `ValidateDestructure`.
        validate_destructure,
        /// Given a struct or union, and a field name as a Ref,
        /// returns the field type. Uses the `pl_node` field. Payload is `FieldTypeRef`.
        field_type_ref,
        /// Given a pointer, initializes all error unions and optionals in the pointee to payloads,
        /// returning the base payload pointer. For instance, converts *E!?T into a valid *T
        /// (clobbering any existing error or null value).
        /// Uses the `un_node` field.
        opt_eu_base_ptr_init,
        /// Coerce a given value such that when a reference is taken, the resulting pointer will be
        /// coercible to the given type. For instance, given a value of type 'u32' and the pointer
        /// type '*u64', coerces the value to a 'u64'. Asserts that the type is a pointer type.
        /// Uses the `pl_node` field. Payload is `Bin`.
        /// LHS is the pointer type, RHS is the value.
        coerce_ptr_elem_ty,
        /// Given a type, validate that it is a pointer type suitable for return from the address-of
        /// operator. Emit a compile error if not.
        /// Uses the `un_tok` union field. Token is the `&` operator. Operand is the type.
        validate_ref_ty,
        /// Given a value, check whether it is a valid local constant in this scope.
        /// In a runtime scope, this is always a nop.
        /// In a comptime scope, raises a compile error if the value is runtime-known.
        /// Result is always void.
        /// Uses the `un_node` union field. Node is the initializer. Operand is the initializer value.
        validate_const,

        // The following tags all relate to struct initialization expressions.

        /// A struct literal with a specified explicit type, with no fields.
        /// Uses the `un_node` field.
        struct_init_empty,
        /// An anonymous struct literal with a known result type, with no fields.
        /// Uses the `un_node` field.
        struct_init_empty_result,
        /// An anonymous struct literal with no fields, returned by reference, with a known result
        /// type for the pointer. Asserts that the type is a pointer.
        /// Uses the `un_node` field.
        struct_init_empty_ref_result,
        /// Struct initialization without a type. Creates a value of an anonymous struct type.
        /// Uses the `pl_node` field. Payload is `StructInitAnon`.
        struct_init_anon,
        /// Finalizes a typed struct or union initialization, performs validation, and returns the
        /// struct or union value. The given type must be validated prior to this instruction, using
        /// `validate_struct_init_ty` or `validate_struct_init_result_ty`. If the given type is
        /// generic poison, this is downgraded to an anonymous initialization.
        /// Uses the `pl_node` field. Payload is `StructInit`.
        struct_init,
        /// Struct initialization syntax, make the result a pointer. Equivalent to `struct_init`
        /// followed by `ref` - this ZIR tag exists as an optimization for a common pattern.
        /// Uses the `pl_node` field. Payload is `StructInit`.
        struct_init_ref,
        /// Checks that the type supports struct init syntax. Always returns void.
        /// Uses the `un_node` field.
        validate_struct_init_ty,
        /// Like `validate_struct_init_ty`, but additionally accepts types which structs coerce to.
        /// Used on the known result type of a struct init expression. Always returns void.
        /// Uses the `un_node` field.
        validate_struct_init_result_ty,
        /// Given a set of `struct_init_field_ptr` instructions, assumes they are all part of a
        /// struct initialization expression, and emits compile errors for duplicate fields as well
        /// as missing fields, if applicable.
        /// This instruction asserts that there is at least one struct_init_field_ptr instruction,
        /// because it must use one of them to find out the struct type.
        /// Uses the `pl_node` field. Payload is `Block`.
        validate_ptr_struct_init,
        /// Given a type being used for a struct initialization expression, returns the type of the
        /// field with the given name.
        /// Uses the `pl_node` field. Payload is `FieldType`.
        struct_init_field_type,
        /// Given a pointer being used as the result pointer of a struct initialization expression,
        /// return a pointer to the field of the given name.
        /// Uses the `pl_node` field. The AST node is the field initializer. Payload is Field.
        struct_init_field_ptr,

        // The following tags all relate to array initialization expressions.

        /// Array initialization without a type. Creates a value of a tuple type.
        /// Uses the `pl_node` field. Payload is `MultiOp`.
        array_init_anon,
        /// Array initialization syntax with a known type. The given type must be validated prior to
        /// this instruction, using some `validate_array_init_*_ty` instruction.
        /// Uses the `pl_node` field. Payload is `MultiOp`, where the first operand is the type.
        array_init,
        /// Array initialization syntax, make the result a pointer. Equivalent to `array_init`
        /// followed by `ref`- this ZIR tag exists as an optimization for a common pattern.
        /// Uses the `pl_node` field. Payload is `MultiOp`, where the first operand is the type.
        array_init_ref,
        /// Checks that the type supports array init syntax. Always returns void.
        /// Uses the `pl_node` field. Payload is `ArrayInit`.
        validate_array_init_ty,
        /// Like `validate_array_init_ty`, but additionally accepts types which arrays coerce to.
        /// Used on the known result type of an array init expression. Always returns void.
        /// Uses the `pl_node` field. Payload is `ArrayInit`.
        validate_array_init_result_ty,
        /// Given a pointer or slice type and an element count, return the expected type of an array
        /// initializer such that a pointer to the initializer has the given pointer type, checking
        /// that this type supports array init syntax and emitting a compile error if not. Preserves
        /// error union and optional wrappers on the array type, if any.
        /// Asserts that the given type is a pointer or slice type.
        /// Uses the `pl_node` field. Payload is `ArrayInitRefTy`.
        validate_array_init_ref_ty,
        /// Given a set of `array_init_elem_ptr` instructions, assumes they are all part of an array
        /// initialization expression, and emits a compile error if the number of elements does not
        /// match the array type.
        /// This instruction asserts that there is at least one `array_init_elem_ptr` instruction,
        /// because it must use one of them to find out the array type.
        /// Uses the `pl_node` field. Payload is `Block`.
        validate_ptr_array_init,
        /// Given a type being used for an array initialization expression, returns the type of the
        /// element at the given index.
        /// Uses the `bin` union field. lhs is the indexable type, rhs is the index.
        array_init_elem_type,
        /// Given a pointer being used as the result pointer of an array initialization expression,
        /// return a pointer to the element at the given index.
        /// Uses the `pl_node` union field. AST node is an element inside array initialization
        /// syntax. Payload is `ElemPtrImm`.
        array_init_elem_ptr,

        /// Implements the `@unionInit` builtin.
        /// Uses the `pl_node` field. Payload is `UnionInit`.
        union_init,
        /// Implements the `@typeInfo` builtin. Uses `un_node`.
        type_info,
        /// Implements the `@sizeOf` builtin. Uses `un_node`.
        size_of,
        /// Implements the `@bitSizeOf` builtin. Uses `un_node`.
        bit_size_of,

        /// Implement builtin `@intFromPtr`. Uses `un_node`.
        /// Convert a pointer to a `usize` integer.
        int_from_ptr,
        /// Emit an error message and fail compilation.
        /// Uses the `un_node` field.
        compile_error,
        /// Changes the maximum number of backwards branches that compile-time
        /// code execution can use before giving up and making a compile error.
        /// Uses the `un_node` union field.
        set_eval_branch_quota,
        /// Converts an enum value into an integer. Resulting type will be the tag type
        /// of the enum. Uses `un_node`.
        int_from_enum,
        /// Implements the `@backingInt` builtin.
        /// Uses `un_node`.
        backing_int,
        /// Implement builtin `@alignOf`. Uses `un_node`.
        align_of,
        /// Implement builtin `@intFromBool`. Uses `un_node`.
        int_from_bool,
        /// Implement builtin `@embedFile`. Uses `un_node`.
        embed_file,
        /// Implement builtin `@errorName`. Uses `un_node`.
        error_name,
        /// Implement builtin `@panic`. Uses `un_node`.
        panic,
        /// Implements `@trap`.
        /// Uses the `node` field.
        trap,
        /// Implement builtin `@setRuntimeSafety`. Uses `un_node`.
        set_runtime_safety,
        /// Implement builtin `@sqrt`. Uses `un_node`.
        sqrt,
        /// Implement builtin `@sin`. Uses `un_node`.
        sin,
        /// Implement builtin `@cos`. Uses `un_node`.
        cos,
        /// Implement builtin `@tan`. Uses `un_node`.
        tan,
        /// Implement builtin `@exp`. Uses `un_node`.
        exp,
        /// Implement builtin `@exp2`. Uses `un_node`.
        exp2,
        /// Implement builtin `@log`. Uses `un_node`.
        log,
        /// Implement builtin `@log2`. Uses `un_node`.
        log2,
        /// Implement builtin `@log10`. Uses `un_node`.
        log10,
        /// Implement builtin `@abs`. Uses `un_node`.
        abs,
        /// Implement builtin `@floor`. Uses `un_node`.
        floor,
        /// Implement builtin `@ceil`. Uses `un_node`.
        ceil,
        /// Implement builtin `@trunc`. Uses `un_node`.
        trunc,
        /// Implement builtin `@round`. Uses `un_node`.
        round,
        /// Implement builtin `@tagName`. Uses `un_node`.
        tag_name,
        /// Implement builtin `@typeName`. Uses `un_node`.
        type_name,
        /// Implement builtin `@Frame`. Uses `un_node`.
        frame_type,

        /// Implements the `@intFromFloat` builtin.
        /// Uses `pl_node` with payload `Bin`. `lhs` is dest type, `rhs` is operand.
        int_from_float,
        /// Implements the `@floatFromInt` builtin.
        /// Uses `pl_node` with payload `Bin`. `lhs` is dest type, `rhs` is operand.
        float_from_int,
        /// Implements the `@ptrFromInt` builtin.
        /// Uses `pl_node` with payload `Bin`. `lhs` is dest type, `rhs` is operand.
        ptr_from_int,
        /// Converts an integer into an enum value.
        /// Uses `pl_node` with payload `Bin`. `lhs` is dest type, `rhs` is operand.
        enum_from_int,
        /// Implements the `@fromBackingInt` builtin.
        /// Uses `pl_node` with payload `Bin`. `lhs` is dest type, `rhs` is operand.
        from_backing_int,
        /// Convert a larger float type to any other float type, possibly causing
        /// a loss of precision.
        /// Uses the `pl_node` field. AST is the `@floatCast` syntax.
        /// Payload is `Bin` with lhs as the dest type, rhs the operand.
        float_cast,
        /// Implements the `@intCast` builtin.
        /// Uses `pl_node` with payload `Bin`. `lhs` is dest type, `rhs` is operand.
        /// Convert an integer value to another integer type, asserting that the destination type
        /// can hold the same mathematical value.
        int_cast,
        /// Implements the `@ptrCast` builtin.
        /// Uses `pl_node` with payload `Bin`. `lhs` is dest type, `rhs` is operand.
        /// Not every `@ptrCast` will correspond to this instruction - see also
        /// `ptr_cast_full` in `Extended`.
        ptr_cast,
        /// Implements the `@truncate` builtin.
        /// Uses `pl_node` with payload `Bin`. `lhs` is dest type, `rhs` is operand.
        truncate,

        /// Implements the `@hasDecl` builtin.
        /// Uses the `pl_node` union field. Payload is `Bin`.
        has_decl,
        /// Implements the `@hasField` builtin.
        /// Uses the `pl_node` union field. Payload is `Bin`.
        has_field,

        /// Implements the `@clz` builtin. Uses the `un_node` union field.
        clz,
        /// Implements the `@ctz` builtin. Uses the `un_node` union field.
        ctz,
        /// Implements the `@popCount` builtin. Uses the `un_node` union field.
        pop_count,
        /// Implements the `@byteSwap` builtin. Uses the `un_node` union field.
        byte_swap,
        /// Implements the `@bitReverse` builtin. Uses the `un_node` union field.
        bit_reverse,

        /// Implements the `@bitOffsetOf` builtin.
        /// Uses the `pl_node` union field with payload `Bin`.
        bit_offset_of,
        /// Implements the `@offsetOf` builtin.
        /// Uses the `pl_node` union field with payload `Bin`.
        offset_of,
        /// Implements the `@splat` builtin.
        /// Uses the `pl_node` union field with payload `Bin`.
        splat,
        /// Implements the `@reduce` builtin.
        /// Uses the `pl_node` union field with payload `Bin`.
        reduce,
        /// Implements the `@shuffle` builtin.
        /// Uses the `pl_node` union field with payload `Shuffle`.
        shuffle,
        /// Implements the `@atomicLoad` builtin.
        /// Uses the `pl_node` union field with payload `AtomicLoad`.
        atomic_load,
        /// Implements the `@atomicRmw` builtin.
        /// Uses the `pl_node` union field with payload `AtomicRmw`.
        atomic_rmw,
        /// Implements the `@atomicStore` builtin.
        /// Uses the `pl_node` union field with payload `AtomicStore`.
        atomic_store,
        /// Implements the `@mulAdd` builtin.
        /// Uses the `pl_node` union field with payload `MulAdd`.
        /// The addend communicates the type of the builtin.
        /// The mulends need to be coerced to the same type.
        mul_add,
        /// Implements the `@memcpy` builtin.
        /// Uses the `pl_node` union field with payload `Bin`.
        memcpy,
        /// Implements the `@memmove` builtin.
        /// Uses the `pl_node` union field with payload `Bin`.
        memmove,
        /// Implements the `@memset` builtin.
        /// Uses the `pl_node` union field with payload `Bin`.
        memset,
        /// Implements the `@min` builtin for 2 args.
        /// Uses the `pl_node` union field with payload `Bin`
        min,
        /// Implements the `@max` builtin for 2 args.
        /// Uses the `pl_node` union field with payload `Bin`
        max,

        /// Allocates stack local memory.
        /// Uses the `un_node` union field. The operand is the type of the allocated object.
        /// The node source location points to a var decl node.
        /// A `make_ptr_const` instruction should be used once the value has
        /// been stored to the allocation. To ensure comptime value detection
        /// functions, there are some restrictions on how this pointer should be
        /// used prior to the `make_ptr_const` instruction: no pointer derived
        /// from this `alloc` may be returned from a block or stored to another
        /// address. In other words, it must be trivial to determine whether any
        /// given pointer derives from this one.
        alloc,
        /// Same as `alloc` except mutable. As such, `make_ptr_const` need not be used,
        /// and there are no restrictions on the usage of the pointer.
        alloc_mut,
        /// Allocates comptime-mutable memory.
        /// Uses the `un_node` union field. The operand is the type of the allocated object.
        /// The node source location points to a var decl node.
        alloc_comptime_mut,
        /// Same as `alloc` except the type is inferred.
        /// Uses the `node` union field.
        alloc_inferred,
        /// Same as `alloc_inferred` except mutable.
        alloc_inferred_mut,
        /// Allocates comptime const memory.
        /// Uses the `node` union field. The type of the allocated object is inferred.
        /// The node source location points to a var decl node.
        alloc_inferred_comptime,
        /// Same as `alloc_comptime_mut` except the type is inferred.
        alloc_inferred_comptime_mut,
        /// Each `store_to_inferred_ptr` puts the type of the stored value into a set,
        /// and then `resolve_inferred_alloc` triggers peer type resolution on the set.
        /// The operand is a `alloc_inferred` or `alloc_inferred_mut` instruction, which
        /// is the allocation that needs to have its type inferred.
        /// Results in the final resolved pointer. The `alloc_inferred[_comptime][_mut]`
        /// instruction should never be referred to after this instruction.
        /// Uses the `un_node` field. The AST node is the var decl.
        resolve_inferred_alloc,
        /// Turns a pointer coming from an `alloc` or `Extended.alloc` into a constant
        /// version of the same pointer. For inferred allocations this is instead implicitly
        /// handled by the `resolve_inferred_alloc` instruction.
        /// Uses the `un_node` union field.
        make_ptr_const,

        /// Implements `resume` syntax. Uses `un_node` field.
        @"resume",

        /// A defer statement.
        /// Uses the `defer` union field.
        @"defer",

        /// Requests that Sema update the saved error return trace index for the enclosing
        /// block, if the operand is .none or of an error/error-union type.
        /// Uses the `save_err_ret_index` field.
        save_err_ret_index,
        /// Specialized form of `Extended.restore_err_ret_index`.
        /// Unconditionally restores the error return index to its last saved state
        /// in the block referred to by `operand`. If `operand` is `none`, restores
        /// to the point of function entry.
        /// Uses the `un_node` field.
        restore_err_ret_index_unconditional,
        /// Specialized form of `Extended.restore_err_ret_index`.
        /// Restores the error return index to its state at the entry of
        /// the current function conditional on `operand` being a non-error.
        /// If `operand` is `none`, restores unconditionally.
        /// Uses the `un_node` field.
        restore_err_ret_index_fn_entry,

        /// The ZIR instruction tag is one of the `Extended` ones.
        /// Uses the `extended` union field.
        extended,

        /// Returns whether the instruction is one of the control flow "noreturn" types.
        /// Function calls do not count.
        pub fn isNoReturn(tag: Tag) bool {
            return switch (tag) {
                .param,
                .param_comptime,
                .param_anytype,
                .param_anytype_comptime,
                .add,
                .addwrap,
                .add_sat,
                .add_unsafe,
                .alloc,
                .alloc_mut,
                .alloc_comptime_mut,
                .alloc_inferred,
                .alloc_inferred_mut,
                .alloc_inferred_comptime,
                .alloc_inferred_comptime_mut,
                .make_ptr_const,
                .array_cat,
                .array_type,
                .array_type_sentinel,
                .reify_int,
                .vector_type,
                .elem_type,
                .indexable_ptr_elem_type,
                .splat_op_result_ty,
                .from_backing_int_arg_ty,
                .indexable_ptr_len,
                .anyframe_type,
                .as_node,
                .as_shift_operand,
                .bit_and,
                .bitcast,
                .bit_or,
                .block,
                .block_comptime,
                .block_inline,
                .declaration,
                .suspend_block,
                .loop,
                .bool_br_and,
                .bool_br_or,
                .bool_not,
                .call,
                .field_call,
                .cmp_lt,
                .cmp_lte,
                .cmp_eq,
                .cmp_gte,
                .cmp_gt,
                .cmp_neq,
                .error_set_decl,
                .dbg_stmt,
                .dbg_var_ptr,
                .dbg_var_val,
                .decl_ref,
                .decl_val,
                .load,
                .div,
                .elem_ptr,
                .elem_val,
                .elem_ptr_node,
                .elem_ptr_load,
                .elem_val_imm,
                .ensure_result_used,
                .ensure_result_non_error,
                .ensure_err_union_payload_void,
                .@"export",
                .field_ptr,
                .field_ptr_load,
                .field_ptr_named,
                .field_ptr_named_load,
                .func,
                .func_inferred,
                .func_fancy,
                .has_decl,
                .int,
                .int_big,
                .float,
                .float128,
                .int_type,
                .is_non_null,
                .is_non_null_ptr,
                .is_non_err,
                .is_non_err_ptr,
                .ret_is_non_err,
                .mod_rem,
                .mul,
                .mulwrap,
                .mul_sat,
                .ref,
                .deref,
                .ref_deref,
                .shl,
                .shl_sat,
                .shr,
                .store_node,
                .store_to_inferred_ptr,
                .str,
                .sub,
                .subwrap,
                .sub_sat,
                .negate,
                .negate_wrap,
                .typeof,
                .typeof_builtin,
                .xor,
                .optional_type,
                .optional_payload_safe,
                .optional_payload_unsafe,
                .optional_payload_safe_ptr,
                .optional_payload_unsafe_ptr,
                .err_union_payload_unsafe,
                .err_union_payload_unsafe_ptr,
                .err_union_code,
                .err_union_code_ptr,
                .ptr_type,
                .enum_literal,
                .decl_literal,
                .decl_literal_no_coerce,
                .merge_error_sets,
                .error_union_type,
                .bit_not,
                .error_value,
                .slice_start,
                .slice_end,
                .slice_sentinel,
                .slice_length,
                .slice_sentinel_ty,
                .import,
                .typeof_log2_int_type,
                .resolve_inferred_alloc,
                .set_eval_branch_quota,
                .switch_block,
                .switch_block_ref,
                .switch_block_err_union,
                .validate_destructure,
                .union_init,
                .field_type_ref,
                .enum_from_int,
                .int_from_enum,
                .backing_int,
                .from_backing_int,
                .type_info,
                .size_of,
                .bit_size_of,
                .int_from_ptr,
                .align_of,
                .int_from_bool,
                .embed_file,
                .error_name,
                .set_runtime_safety,
                .sqrt,
                .sin,
                .cos,
                .tan,
                .exp,
                .exp2,
                .log,
                .log2,
                .log10,
                .abs,
                .floor,
                .ceil,
                .trunc,
                .round,
                .tag_name,
                .type_name,
                .frame_type,
                .int_from_float,
                .float_from_int,
                .ptr_from_int,
                .float_cast,
                .int_cast,
                .ptr_cast,
                .truncate,
                .has_field,
                .clz,
                .ctz,
                .pop_count,
                .byte_swap,
                .bit_reverse,
                .div_exact,
                .div_floor,
                .div_ceil,
                .div_trunc,
                .mod,
                .rem,
                .shl_exact,
                .shr_exact,
                .bit_offset_of,
                .offset_of,
                .splat,
                .reduce,
                .shuffle,
                .atomic_load,
                .atomic_rmw,
                .atomic_store,
                .mul_add,
                .builtin_call,
                .max,
                .memcpy,
                .memset,
                .memmove,
                .min,
                .@"resume",
                .extended,
                .ret_ptr,
                .ret_type,
                .@"try",
                .try_ptr,
                .@"defer",
                .save_err_ret_index,
                .for_len,
                .opt_eu_base_ptr_init,
                .coerce_ptr_elem_ty,
                .struct_init_empty,
                .struct_init_empty_result,
                .struct_init_empty_ref_result,
                .struct_init_anon,
                .struct_init,
                .struct_init_ref,
                .validate_struct_init_ty,
                .validate_struct_init_result_ty,
                .validate_ptr_struct_init,
                .struct_init_field_type,
                .struct_init_field_ptr,
                .array_init_anon,
                .array_init,
                .array_init_ref,
                .validate_array_init_ty,
                .validate_array_init_result_ty,
                .validate_array_init_ref_ty,
                .validate_ptr_array_init,
                .array_init_elem_type,
                .array_init_elem_ptr,
                .validate_ref_ty,
                .validate_const,
                .restore_err_ret_index_unconditional,
                .restore_err_ret_index_fn_entry,
                => false,

                .@"break",
                .break_inline,
                .condbr,
                .condbr_inline,
                .compile_error,
                .ret_node,
                .ret_load,
                .ret_implicit,
                .ret_err_value,
                .@"unreachable",
                .repeat,
                .repeat_inline,
                .panic,
                .trap,
                .check_comptime_control_flow,
                .switch_continue,
                => true,
            };
        }

        /// AstGen uses this to find out if `Ref.void_value` should be used in place
        /// of the result of a given instruction. This allows Sema to forego adding
        /// the instruction to the map after analysis.
        pub fn isAlwaysVoid(tag: Tag, data: Data) bool {
            return switch (tag) {
                .dbg_stmt,
                .dbg_var_ptr,
                .dbg_var_val,
                .ensure_result_used,
                .ensure_result_non_error,
                .ensure_err_union_payload_void,
                .set_eval_branch_quota,
                .atomic_store,
                .store_node,
                .store_to_inferred_ptr,
                .validate_destructure,
                .@"export",
                .set_runtime_safety,
                .memcpy,
                .memset,
                .memmove,
                .check_comptime_control_flow,
                .@"defer",
                .save_err_ret_index,
                .restore_err_ret_index_unconditional,
                .restore_err_ret_index_fn_entry,
                .validate_struct_init_ty,
                .validate_struct_init_result_ty,
                .validate_ptr_struct_init,
                .validate_array_init_ty,
                .validate_array_init_result_ty,
                .validate_ptr_array_init,
                .validate_ref_ty,
                .validate_const,
                => true,

                .param,
                .param_comptime,
                .param_anytype,
                .param_anytype_comptime,
                .add,
                .addwrap,
                .add_sat,
                .add_unsafe,
                .alloc,
                .alloc_mut,
                .alloc_comptime_mut,
                .alloc_inferred,
                .alloc_inferred_mut,
                .alloc_inferred_comptime,
                .alloc_inferred_comptime_mut,
                .resolve_inferred_alloc,
                .make_ptr_const,
                .array_cat,
                .array_type,
                .array_type_sentinel,
                .reify_int,
                .vector_type,
                .elem_type,
                .indexable_ptr_elem_type,
                .splat_op_result_ty,
                .from_backing_int_arg_ty,
                .indexable_ptr_len,
                .anyframe_type,
                .as_node,
                .as_shift_operand,
                .bit_and,
                .bitcast,
                .bit_or,
                .block,
                .block_comptime,
                .block_inline,
                .declaration,
                .suspend_block,
                .loop,
                .bool_br_and,
                .bool_br_or,
                .bool_not,
                .call,
                .field_call,
                .cmp_lt,
                .cmp_lte,
                .cmp_eq,
                .cmp_gte,
                .cmp_gt,
                .cmp_neq,
                .error_set_decl,
                .decl_ref,
                .decl_val,
                .load,
                .div,
                .elem_ptr,
                .elem_val,
                .elem_ptr_node,
                .elem_ptr_load,
                .elem_val_imm,
                .field_ptr,
                .field_ptr_load,
                .field_ptr_named,
                .field_ptr_named_load,
                .func,
                .func_inferred,
                .func_fancy,
                .has_decl,
                .int,
                .int_big,
                .float,
                .float128,
                .int_type,
                .is_non_null,
                .is_non_null_ptr,
                .is_non_err,
                .is_non_err_ptr,
                .ret_is_non_err,
                .mod_rem,
                .mul,
                .mulwrap,
                .mul_sat,
                .ref,
                .deref,
                .ref_deref,
                .shl,
                .shl_sat,
                .shr,
                .str,
                .sub,
                .subwrap,
                .sub_sat,
                .negate,
                .negate_wrap,
                .typeof,
                .typeof_builtin,
                .xor,
                .optional_type,
                .optional_payload_safe,
                .optional_payload_unsafe,
                .optional_payload_safe_ptr,
                .optional_payload_unsafe_ptr,
                .err_union_payload_unsafe,
                .err_union_payload_unsafe_ptr,
                .err_union_code,
                .err_union_code_ptr,
                .ptr_type,
                .enum_literal,
                .decl_literal,
                .decl_literal_no_coerce,
                .merge_error_sets,
                .error_union_type,
                .bit_not,
                .error_value,
                .slice_start,
                .slice_end,
                .slice_sentinel,
                .slice_length,
                .slice_sentinel_ty,
                .import,
                .typeof_log2_int_type,
                .switch_block,
                .switch_block_ref,
                .switch_block_err_union,
                .union_init,
                .field_type_ref,
                .enum_from_int,
                .int_from_enum,
                .backing_int,
                .from_backing_int,
                .type_info,
                .size_of,
                .bit_size_of,
                .int_from_ptr,
                .align_of,
                .int_from_bool,
                .embed_file,
                .error_name,
                .sqrt,
                .sin,
                .cos,
                .tan,
                .exp,
                .exp2,
                .log,
                .log2,
                .log10,
                .abs,
                .floor,
                .ceil,
                .trunc,
                .round,
                .tag_name,
                .type_name,
                .frame_type,
                .int_from_float,
                .float_from_int,
                .ptr_from_int,
                .float_cast,
                .int_cast,
                .ptr_cast,
                .truncate,
                .has_field,
                .clz,
                .ctz,
                .pop_count,
                .byte_swap,
                .bit_reverse,
                .div_exact,
                .div_floor,
                .div_ceil,
                .div_trunc,
                .mod,
                .rem,
                .shl_exact,
                .shr_exact,
                .bit_offset_of,
                .offset_of,
                .splat,
                .reduce,
                .shuffle,
                .atomic_load,
                .atomic_rmw,
                .mul_add,
                .builtin_call,
                .max,
                .min,
                .@"resume",
                .@"break",
                .break_inline,
                .condbr,
                .condbr_inline,
                .switch_continue,
                .compile_error,
                .ret_node,
                .ret_load,
                .ret_implicit,
                .ret_err_value,
                .ret_ptr,
                .ret_type,
                .@"unreachable",
                .repeat,
                .repeat_inline,
                .panic,
                .trap,
                .for_len,
                .@"try",
                .try_ptr,
                .opt_eu_base_ptr_init,
                .coerce_ptr_elem_ty,
                .struct_init_empty,
                .struct_init_empty_result,
                .struct_init_empty_ref_result,
                .struct_init_anon,
                .struct_init,
                .struct_init_ref,
                .struct_init_field_type,
                .struct_init_field_ptr,
                .array_init_anon,
                .array_init,
                .array_init_ref,
                .validate_array_init_ref_ty,
                .array_init_elem_type,
                .array_init_elem_ptr,
                => false,

                .extended => switch (data.extended.opcode) {
                    .branch_hint,
                    .breakpoint,
                    .disable_instrumentation,
                    .disable_intrinsics,
                    => true,
                    else => false,
                },
            };
        }

        /// Used by debug safety-checking code.
        pub const data_tags = list: {
            @setEvalBranchQuota(2000);
            break :list std.enums.directEnumArray(Tag, Data.FieldEnum, 0, .{
                .add = .pl_node,
                .addwrap = .pl_node,
                .add_sat = .pl_node,
                .add_unsafe = .pl_node,
                .sub = .pl_node,
                .subwrap = .pl_node,
                .sub_sat = .pl_node,
                .mul = .pl_node,
                .mulwrap = .pl_node,
                .mul_sat = .pl_node,

                .param = .pl_tok,
                .param_comptime = .pl_tok,
                .param_anytype = .str_tok,
                .param_anytype_comptime = .str_tok,
                .array_cat = .pl_node,
                .array_type = .pl_node,
                .array_type_sentinel = .pl_node,
                .reify_int = .pl_node,
                .vector_type = .pl_node,
                .elem_type = .un_node,
                .indexable_ptr_elem_type = .un_node,
                .splat_op_result_ty = .un_node,
                .from_backing_int_arg_ty = .un_node,
                .indexable_ptr_len = .un_node,
                .anyframe_type = .un_node,
                .as_node = .pl_node,
                .as_shift_operand = .pl_node,
                .bit_and = .pl_node,
                .bitcast = .pl_node,
                .bit_not = .un_node,
                .bit_or = .pl_node,
                .block = .pl_node,
                .block_comptime = .pl_node,
                .block_inline = .pl_node,
                .declaration = .declaration,
                .suspend_block = .pl_node,
                .bool_not = .un_node,
                .bool_br_and = .pl_node,
                .bool_br_or = .pl_node,
                .@"break" = .@"break",
                .break_inline = .@"break",
                .switch_continue = .@"break",
                .check_comptime_control_flow = .un_node,
                .for_len = .pl_node,
                .call = .pl_node,
                .field_call = .pl_node,
                .cmp_lt = .pl_node,
                .cmp_lte = .pl_node,
                .cmp_eq = .pl_node,
                .cmp_gte = .pl_node,
                .cmp_gt = .pl_node,
                .cmp_neq = .pl_node,
                .condbr = .pl_node,
                .condbr_inline = .pl_node,
                .@"try" = .pl_node,
                .try_ptr = .pl_node,
                .error_set_decl = .pl_node,
                .dbg_stmt = .dbg_stmt,
                .dbg_var_ptr = .str_op,
                .dbg_var_val = .str_op,
                .decl_ref = .str_tok,
                .decl_val = .str_tok,
                .load = .un_node,
                .div = .pl_node,
                .elem_ptr = .pl_node,
                .elem_ptr_node = .pl_node,
                .elem_val = .pl_node,
                .elem_ptr_load = .pl_node,
                .elem_val_imm = .elem_val_imm,
                .ensure_result_used = .un_node,
                .ensure_result_non_error = .un_node,
                .ensure_err_union_payload_void = .un_node,
                .error_union_type = .pl_node,
                .error_value = .str_tok,
                .@"export" = .pl_node,
                .field_ptr = .pl_node,
                .field_ptr_load = .pl_node,
                .field_ptr_named = .pl_node,
                .field_ptr_named_load = .pl_node,
                .func = .pl_node,
                .func_inferred = .pl_node,
                .func_fancy = .pl_node,
                .import = .pl_tok,
                .int = .int,
                .int_big = .str,
                .float = .float,
                .float128 = .pl_node,
                .int_type = .int_type,
                .is_non_null = .un_node,
                .is_non_null_ptr = .un_node,
                .is_non_err = .un_node,
                .is_non_err_ptr = .un_node,
                .ret_is_non_err = .un_node,
                .loop = .pl_node,
                .repeat = .node,
                .repeat_inline = .node,
                .merge_error_sets = .pl_node,
                .mod_rem = .pl_node,
                .ref = .un_tok,
                .deref = .un_node,
                .ref_deref = .un_node,
                .ret_node = .un_node,
                .ret_load = .un_node,
                .ret_implicit = .un_tok,
                .ret_err_value = .str_tok,
                .ret_ptr = .node,
                .ret_type = .node,
                .ptr_type = .ptr_type,
                .slice_start = .pl_node,
                .slice_end = .pl_node,
                .slice_sentinel = .pl_node,
                .slice_length = .pl_node,
                .slice_sentinel_ty = .un_node,
                .store_node = .pl_node,
                .store_to_inferred_ptr = .pl_node,
                .str = .str,
                .negate = .un_node,
                .negate_wrap = .un_node,
                .typeof = .un_node,
                .typeof_log2_int_type = .un_node,
                .@"unreachable" = .@"unreachable",
                .xor = .pl_node,
                .optional_type = .un_node,
                .optional_payload_safe = .un_node,
                .optional_payload_unsafe = .un_node,
                .optional_payload_safe_ptr = .un_node,
                .optional_payload_unsafe_ptr = .un_node,
                .err_union_payload_unsafe = .un_node,
                .err_union_payload_unsafe_ptr = .un_node,
                .err_union_code = .un_node,
                .err_union_code_ptr = .un_node,
                .enum_literal = .str_tok,
                .decl_literal = .pl_node,
                .decl_literal_no_coerce = .pl_node,
                .switch_block = .pl_node,
                .switch_block_ref = .pl_node,
                .switch_block_err_union = .pl_node,
                .validate_destructure = .pl_node,
                .field_type_ref = .pl_node,
                .union_init = .pl_node,
                .type_info = .un_node,
                .size_of = .un_node,
                .bit_size_of = .un_node,
                .opt_eu_base_ptr_init = .un_node,
                .coerce_ptr_elem_ty = .pl_node,
                .validate_ref_ty = .un_tok,
                .validate_const = .un_node,

                .int_from_ptr = .un_node,
                .compile_error = .un_node,
                .set_eval_branch_quota = .un_node,
                .int_from_enum = .un_node,
                .backing_int = .un_node,
                .align_of = .un_node,
                .int_from_bool = .un_node,
                .embed_file = .un_node,
                .error_name = .un_node,
                .panic = .un_node,
                .trap = .node,
                .set_runtime_safety = .un_node,
                .sqrt = .un_node,
                .sin = .un_node,
                .cos = .un_node,
                .tan = .un_node,
                .exp = .un_node,
                .exp2 = .un_node,
                .log = .un_node,
                .log2 = .un_node,
                .log10 = .un_node,
                .abs = .un_node,
                .floor = .un_node,
                .ceil = .un_node,
                .trunc = .un_node,
                .round = .un_node,
                .tag_name = .un_node,
                .type_name = .un_node,
                .frame_type = .un_node,

                .int_from_float = .pl_node,
                .float_from_int = .pl_node,
                .ptr_from_int = .pl_node,
                .enum_from_int = .pl_node,
                .from_backing_int = .pl_node,
                .float_cast = .pl_node,
                .int_cast = .pl_node,
                .ptr_cast = .pl_node,
                .truncate = .pl_node,
                .typeof_builtin = .pl_node,

                .has_decl = .pl_node,
                .has_field = .pl_node,

                .clz = .un_node,
                .ctz = .un_node,
                .pop_count = .un_node,
                .byte_swap = .un_node,
                .bit_reverse = .un_node,

                .div_exact = .pl_node,
                .div_floor = .pl_node,
                .div_ceil = .pl_node,
                .div_trunc = .pl_node,
                .mod = .pl_node,
                .rem = .pl_node,

                .shl = .pl_node,
                .shl_exact = .pl_node,
                .shl_sat = .pl_node,
                .shr = .pl_node,
                .shr_exact = .pl_node,

                .bit_offset_of = .pl_node,
                .offset_of = .pl_node,
                .splat = .pl_node,
                .reduce = .pl_node,
                .shuffle = .pl_node,
                .atomic_load = .pl_node,
                .atomic_rmw = .pl_node,
                .atomic_store = .pl_node,
                .mul_add = .pl_node,
                .builtin_call = .pl_node,
                .max = .pl_node,
                .memcpy = .pl_node,
                .memset = .pl_node,
                .memmove = .pl_node,
                .min = .pl_node,

                .alloc = .un_node,
                .alloc_mut = .un_node,
                .alloc_comptime_mut = .un_node,
                .alloc_inferred = .node,
                .alloc_inferred_mut = .node,
                .alloc_inferred_comptime = .node,
                .alloc_inferred_comptime_mut = .node,
                .resolve_inferred_alloc = .un_node,
                .make_ptr_const = .un_node,

                .@"resume" = .un_node,

                .@"defer" = .@"defer",

                .save_err_ret_index = .save_err_ret_index,
                .restore_err_ret_index_unconditional = .un_node,
                .restore_err_ret_index_fn_entry = .un_node,

                .struct_init_empty = .un_node,
                .struct_init_empty_result = .un_node,
                .struct_init_empty_ref_result = .un_node,
                .struct_init_anon = .pl_node,
                .struct_init = .pl_node,
                .struct_init_ref = .pl_node,
                .validate_struct_init_ty = .un_node,
                .validate_struct_init_result_ty = .un_node,
                .validate_ptr_struct_init = .pl_node,
                .struct_init_field_type = .pl_node,
                .struct_init_field_ptr = .pl_node,
                .array_init_anon = .pl_node,
                .array_init = .pl_node,
                .array_init_ref = .pl_node,
                .validate_array_init_ty = .pl_node,
                .validate_array_init_result_ty = .pl_node,
                .validate_array_init_ref_ty = .pl_node,
                .validate_ptr_array_init = .pl_node,
                .array_init_elem_type = .bin,
                .array_init_elem_ptr = .pl_node,

                .extended = .extended,
            });
        };

        // Uncomment to view how many tag slots are available.
        //comptime {
        //    @compileLog("ZIR tags left: ", 256 - @typeInfo(Tag).@"enum".field_names.len);
        //}
    };

    /// Rarer instructions are here; ones that do not fit in the 8-bit `Tag` enum.
    /// `noreturn` instructions may not go here; they must be part of the main `Tag` enum.
    pub const Extended = enum(u16) {
        /// A struct type definition. Contains references to ZIR instructions for
        /// the field types, defaults, and alignments.
        /// `operand` is payload index to `StructDecl`.
        /// `small` is `StructDecl.Small`.
        struct_decl,
        /// An enum type definition. Contains references to ZIR instructions for
        /// the field value expressions and optional type tag expression.
        /// `operand` is payload index to `EnumDecl`.
        /// `small` is `EnumDecl.Small`.
        enum_decl,
        /// A union type definition. Contains references to ZIR instructions for
        /// the field types and optional type tag expression.
        /// `operand` is payload index to `UnionDecl`.
        /// `small` is `UnionDecl.Small`.
        union_decl,
        /// An opaque type definition. Contains references to decls and captures.
        /// `operand` is payload index to `OpaqueDecl`.
        /// `small` is `OpaqueDecl.Small`.
        opaque_decl,
        /// A tuple type. Note that tuples are not namespace/container types.
        /// `operand` is payload index to `TupleDecl`.
        /// `small` is `fields_len: u16`.
        tuple_decl,
        /// Implements the `@This` builtin.
        /// `operand` is `src_node: Ast.Node.Offset`.
        this,
        /// Implements the `@returnAddress` builtin.
        /// `operand` is `src_node: Ast.Node.Offset`.
        ret_addr,
        /// Implements the `@src` builtin.
        /// `operand` is payload index to `LineColumn`.
        builtin_src,
        /// Implements the `@errorReturnTrace` builtin.
        /// `operand` is `src_node: Ast.Node.Offset`.
        error_return_trace,
        /// Implements the `@frame` builtin.
        /// `operand` is `src_node: Ast.Node.Offset`.
        frame,
        /// Implements the `@frameAddress` builtin.
        /// `operand` is `src_node: Ast.Node.Offset`.
        frame_address,
        /// Same as `alloc` from `Tag` but may contain an alignment instruction.
        /// `operand` is payload index to `AllocExtended`.
        /// `small`:
        ///  * 0b000X - has type
        ///  * 0b00X0 - has alignment
        ///  * 0b0X00 - 1=const, 0=var
        ///  * 0bX000 - is comptime
        alloc,
        /// The `@extern` builtin.
        /// `operand` is payload index to `BinNode`.
        builtin_extern,
        /// Inline assembly.
        /// `operand` is payload index to `Asm`.
        @"asm",
        /// Same as `asm` except the assembly template is not a string literal but a comptime
        /// expression.
        /// The `asm_source` field of the Asm is not a null-terminated string
        /// but instead a Ref.
        asm_expr,
        /// Log compile time variables and emit an error message.
        /// `operand` is payload index to `NodeMultiOp`.
        /// `small` is `operands_len`.
        /// The AST node is the compile log builtin call.
        compile_log,
        /// The builtin `@TypeOf` which returns the type after Peer Type Resolution
        /// of one or more params.
        /// `operand` is payload index to `TypeOfPeer`.
        /// `small` is `operands_len`.
        /// The AST node is the builtin call.
        typeof_peer,
        /// Implements the `@min` builtin for more than 2 args.
        /// `operand` is payload index to `NodeMultiOp`.
        /// `small` is `operands_len`.
        /// The AST node is the builtin call.
        min_multi,
        /// Implements the `@max` builtin for more than 2 args.
        /// `operand` is payload index to `NodeMultiOp`.
        /// `small` is `operands_len`.
        /// The AST node is the builtin call.
        max_multi,
        /// Implements the `@addWithOverflow` builtin.
        /// `operand` is payload index to `BinNode`.
        /// `small` is unused.
        add_with_overflow,
        /// Implements the `@subWithOverflow` builtin.
        /// `operand` is payload index to `BinNode`.
        /// `small` is unused.
        sub_with_overflow,
        /// Implements the `@mulWithOverflow` builtin.
        /// `operand` is payload index to `BinNode`.
        /// `small` is unused.
        mul_with_overflow,
        /// Implements the `@shlWithOverflow` builtin.
        /// `operand` is payload index to `BinNode`.
        /// `small` is unused.
        shl_with_overflow,
        /// `@round`, `@floor`, `@ceil`, or `@trunc`, with a result type.
        /// `operand` is payload index to `BinNode`.
        /// `small` is a `RoundOp` representing the specific operation being performed.
        round_op,
        /// Returns the type for the operand of a rounding op.
        /// `operand` is `UnNode`.
        /// `small` is unused.
        round_op_ty,
        /// `operand` is payload index to `UnNode`.
        wasm_memory_size,
        /// `operand` is payload index to `BinNode`.
        wasm_memory_grow,
        /// The `@prefetch` builtin.
        /// `operand` is payload index to `BinNode`.
        prefetch,
        /// Implement builtin `@setFloatMode`.
        /// `operand` is payload index to `UnNode`.
        set_float_mode,
        /// Implements the `@errorCast` builtin.
        /// `operand` is payload index to `BinNode`. `lhs` is dest type, `rhs` is operand.
        error_cast,
        /// Implements `@breakpoint`.
        /// `operand` is `src_node: Ast.Node.Offset`.
        breakpoint,
        /// Implement builtin `@disableInstrumentation`. `operand` is `src_node: Ast.Node.Offset`.
        disable_instrumentation,
        /// Implement builtin `@disableIntrinsics`. `operand` is `src_node: i32`.
        disable_intrinsics,
        /// Implements the `@select` builtin.
        /// `operand` is payload index to `Select`.
        select,
        /// Implement builtin `@errToInt`.
        /// `operand` is payload index to `UnNode`.
        int_from_error,
        /// Implement builtin `@errorFromInt`.
        /// `operand` is payload index to `UnNode`.
        error_from_int,
        /// Given a comptime-known operand of type `[]const A`, returns the type `*const [operand.len]B`.
        /// The types `A` and `B` are determined from `ReifySliceArgInfo`.
        /// This instruction is used to provide result types to arguments of `@Fn`, `@Struct`, etc.
        /// `operand` is payload index to `UnNode`.
        /// `small` is a bitcast `ReifySliceArgInfo`.
        reify_slice_arg_ty,
        /// Like `reify_slice_arg_ty` for the specific case of `[]const []const u8` to `[]const TagInt`,
        /// as needed for `@Enum`.
        /// `operand` is payload index to `BinNode`. lhs is the type `TagInt`. rhs is the `[]const []const u8` value.
        /// `small` is unused.
        reify_enum_value_slice_ty,
        /// Given a comptime-known operand of type `type`, returns the type `?operand` if possible, otherwise `?noreturn`.
        /// Used for the final arg of `@Pointer` to allow reifying pointers to opaque types.
        /// `operand` is payload index to `UnNode`.
        /// `small` is unused.
        reify_pointer_sentinel_ty,
        /// Implements builtin `@Tuple`.
        /// `operand` is payload index to `UnNode`.
        reify_tuple,
        /// Implements builtin `@Pointer`.
        /// `operand` is payload index to `ReifyPointer`.
        reify_pointer,
        /// Implements builtin `@Fn`.
        /// `operand` is payload index to `ReifyFn`.
        reify_fn,
        /// Implements builtin `@Struct`.
        /// `operand` is payload index to `ReifyStruct`.
        /// `small` contains `NameStrategy`.
        reify_struct,
        /// Implements builtin `@Union`.
        /// `operand` is payload index to `ReifyUnion`.
        /// `small` contains `NameStrategy`.
        reify_union,
        /// Implements builtin `@Enum`.
        /// `operand` is payload index to `ReifyEnum`.
        /// `small` contains `NameStrategy`.
        reify_enum,
        /// Implements builtin `@SpirvType`.
        /// `operand` is payload index to `ReifyFn`.
        reify_spirv_type,
        /// Implements the `@cmpxchgStrong` and `@cmpxchgWeak` builtins.
        /// `small` 0=>weak 1=>strong
        /// `operand` is payload index to `Cmpxchg`.
        cmpxchg,
        /// Implement builtin `@cVaArg`.
        /// `operand` is payload index to `BinNode`.
        c_va_arg,
        /// Implement builtin `@cVaCopy`.
        /// `operand` is payload index to `UnNode`.
        c_va_copy,
        /// Implement builtin `@cVaEnd`.
        /// `operand` is payload index to `UnNode`.
        c_va_end,
        /// Implement builtin `@cVaStart`.
        /// `operand` is `src_node: Ast.Node.Offset`.
        c_va_start,
        /// Implements the following builtins:
        /// `@ptrCast`, `@alignCast`, `@addrSpaceCast`, `@constCast`, `@volatileCast`.
        /// Represents an arbitrary nesting of the above builtins. Such a nesting is treated as a
        /// single operation which can modify multiple components of a pointer type.
        /// `operand` is payload index to `BinNode`.
        /// `small` contains `FullPtrCastFlags`.
        /// AST node is the root of the nested casts.
        /// `lhs` is dest type, `rhs` is operand.
        ptr_cast_full,
        /// `operand` is payload index to `UnNode`.
        /// `small` contains `FullPtrCastFlags`.
        /// Guaranteed to only have flags where no explicit destination type is
        /// required (const_cast and volatile_cast).
        /// AST node is the root of the nested casts.
        ptr_cast_no_dest,
        /// Implements the `@workItemId` builtin.
        /// `operand` is payload index to `UnNode`.
        work_item_id,
        /// Implements the `@workGroupSize` builtin.
        /// `operand` is payload index to `UnNode`.
        work_group_size,
        /// Implements the `@workGroupId` builtin.
        /// `operand` is payload index to `UnNode`.
        work_group_id,
        /// Implements the `@inComptime` builtin.
        /// `operand` is `src_node: Ast.Node.Offset`.
        in_comptime,
        /// Restores the error return index to its last saved state in a given
        /// block. If the block is `.none`, restores to the state from the point
        /// of function entry. If the operand is not `.none`, the restore is
        /// conditional on the operand value not being an error.
        /// `operand` is payload index to `RestoreErrRetIndex`.
        /// `small` is undefined.
        restore_err_ret_index,
        /// Retrieves a value from the current type declaration scope's closure.
        /// `operand` is `src_node: Ast.Node.Offset`.
        /// `small` is closure index.
        closure_get,
        /// Used as a placeholder instruction which is just a dummy index for Sema to replace
        /// with a specific value. For instance, this is used for the capture of an `errdefer`.
        /// This should never appear in a body.
        value_placeholder,
        /// Implements the `@fieldParentPtr` builtin.
        /// `operand` is payload index to `FieldParentPtr`.
        /// `small` contains `FullPtrCastFlags`.
        /// Guaranteed to not have the `ptr_cast` flag.
        /// Uses the `pl_node` union field with payload `FieldParentPtr`.
        field_parent_ptr,
        /// Get a type or value from `std.lang`.
        /// `operand` is `src_node: Ast.Node.Offset`.
        /// `small` is an `Inst.StdLangValue`.
        std_lang_value,
        /// Provide a `@branchHint` for the current block.
        /// `operand` is payload index to `UnNode`.
        /// `small` is unused.
        branch_hint,
        /// Compute the result type for in-place arithmetic, e.g. `+=`.
        /// `operand` is `Zir.Inst.Ref` of the loaded LHS (*not* its type).
        /// `small` is an `Inst.InplaceOp`.
        inplace_arith_result_ty,
        /// Marks a statement that can be stepped to but produces no code.
        /// `operand` and `small` are ignored.
        dbg_empty_stmt,
        /// At this point, AstGen encountered a fatal error which terminated ZIR lowering for this body.
        /// A file-level error has been reported. Sema should terminate semantic analysis.
        /// `operand` and `small` are ignored.
        /// This instruction is always `noreturn`, however, it is not considered as such by ZIR-level queries. This allows AstGen to assume that
        /// any code may have gone here, avoiding false-positive "unreachable code" errors.
        astgen_error,
        /// Given a type, strips away any error unions or optionals stacked
        /// on top and returns the base type. That base type must be a float.
        /// For example: Provided with `error{Foo}!?f64`, returns `f64`.
        /// `operand` is payload index to `UnNode`.
        float_op_result_ty,

        pub const InstData = struct {
            opcode: Extended,
            small: u16,
            operand: u32,
        };
    };

    /// The position of a ZIR instruction within the `Zir` instructions array.
    pub const Index = enum(u32) {
        /// ZIR is structured so that the outermost "main" struct of any file
        /// is always at index 0.
        main_struct_inst = 0,
        _,

        pub fn toRef(i: Index) Inst.Ref {
            return @fromBackingInt(@intCast(Ref.static_len + @backingInt(i)));
        }

        pub fn toOptional(i: Index) OptionalIndex {
            return @fromBackingInt(@intCast(@backingInt(i)));
        }
    };

    pub const OptionalIndex = enum(u32) {
        /// ZIR is structured so that the outermost "main" struct of any file
        /// is always at index 0.
        main_struct_inst = 0,
        none = std.math.maxInt(u32),
        _,

        pub fn unwrap(oi: OptionalIndex) ?Index {
            return if (oi == .none) null else @fromBackingInt(@intCast(@backingInt(oi)));
        }
    };

    /// A reference to ZIR instruction, or to an InternPool index, or neither.
    ///
    /// If the integer tag value is < InternPool.static_len, then it
    /// corresponds to an InternPool index. Otherwise, this refers to a ZIR
    /// instruction.
    ///
    /// The tag type is specified so that it is safe to bitcast between `[]u32`
    /// and `[]Ref`.
    pub const Ref = enum(u32) {
        u0_type,
        u1_type,
        u8_type,
        i8_type,
        u16_type,
        i16_type,
        u29_type,
        u32_type,
        i32_type,
        u64_type,
        i64_type,
        u80_type,
        u128_type,
        i128_type,
        u256_type,
        usize_type,
        isize_type,
        c_char_type,
        c_short_type,
        c_ushort_type,
        c_int_type,
        c_uint_type,
        c_long_type,
        c_ulong_type,
        c_longlong_type,
        c_ulonglong_type,
        c_longdouble_type,
        f16_type,
        f32_type,
        f64_type,
        f80_type,
        f128_type,
        anyopaque_type,
        bool_type,
        void_type,
        type_type,
        anyerror_type,
        comptime_int_type,
        comptime_float_type,
        noreturn_type,
        anyframe_type,
        null_type,
        undefined_type,
        enum_literal_type,
        ptr_usize_type,
        ptr_const_comptime_int_type,
        manyptr_u8_type,
        manyptr_const_u8_type,
        manyptr_const_u8_sentinel_0_type,
        slice_const_u8_type,
        slice_const_u8_sentinel_0_type,
        manyptr_const_slice_const_u8_type,
        slice_const_slice_const_u8_type,
        optional_type_type,
        manyptr_const_type_type,
        slice_const_type_type,
        vector_8_i8_type,
        vector_16_i8_type,
        vector_32_i8_type,
        vector_64_i8_type,
        vector_1_u8_type,
        vector_2_u8_type,
        vector_4_u8_type,
        vector_8_u8_type,
        vector_16_u8_type,
        vector_32_u8_type,
        vector_64_u8_type,
        vector_2_i16_type,
        vector_4_i16_type,
        vector_8_i16_type,
        vector_16_i16_type,
        vector_32_i16_type,
        vector_4_u16_type,
        vector_8_u16_type,
        vector_16_u16_type,
        vector_32_u16_type,
        vector_2_i32_type,
        vector_4_i32_type,
        vector_8_i32_type,
        vector_16_i32_type,
        vector_4_u32_type,
        vector_8_u32_type,
        vector_16_u32_type,
        vector_2_i64_type,
        vector_4_i64_type,
        vector_8_i64_type,
        vector_2_u64_type,
        vector_4_u64_type,
        vector_8_u64_type,
        vector_1_u128_type,
        vector_2_u128_type,
        vector_1_u256_type,
        vector_4_f16_type,
        vector_8_f16_type,
        vector_16_f16_type,
        vector_32_f16_type,
        vector_2_f32_type,
        vector_4_f32_type,
        vector_8_f32_type,
        vector_16_f32_type,
        vector_2_f64_type,
        vector_4_f64_type,
        vector_8_f64_type,
        optional_noreturn_type,
        anyerror_void_error_union_type,
        adhoc_inferred_error_set_type,
        generic_poison_type,
        empty_tuple_type,
        undef,
        undef_bool,
        undef_usize,
        undef_u1,
        zero,
        zero_usize,
        zero_u1,
        zero_u8,
        one,
        one_usize,
        one_u1,
        one_u8,
        four_u8,
        negative_one,
        void_value,
        unreachable_value,
        null_value,
        bool_true,
        bool_false,
        empty_tuple,

        /// This Ref does not correspond to any ZIR instruction or constant
        /// value and may instead be used as a sentinel to indicate null.
        none = std.math.maxInt(u32),

        _,

        pub const static_len = @typeInfo(@This()).@"enum".field_names.len - 1;

        pub fn toIndex(inst: Ref) ?Index {
            assert(inst != .none);
            const ref_int = @backingInt(inst);
            if (ref_int >= static_len) {
                return @fromBackingInt(@intCast(ref_int - static_len));
            } else {
                return null;
            }
        }

        pub fn toIndexAllowNone(inst: Ref) ?Index {
            if (inst == .none) return null;
            return toIndex(inst);
        }
    };

    /// All instructions have an 8-byte payload, which is contained within
    /// this union. `Tag` determines which union field is active, as well as
    /// how to interpret the data within.
    pub const Data = union {
        /// Used for `Tag.extended`. The extended opcode determines the meaning
        /// of the `small` and `operand` fields.
        extended: Extended.InstData,
        /// Used for unary operators, with an AST node source location.
        un_node: struct {
            /// Offset from Decl AST node index.
            src_node: Ast.Node.Offset,
            /// The meaning of this operand depends on the corresponding `Tag`.
            operand: Ref,
        },
        /// Used for unary operators, with a token source location.
        un_tok: struct {
            /// Offset from Decl AST token index.
            src_tok: Ast.TokenOffset,
            /// The meaning of this operand depends on the corresponding `Tag`.
            operand: Ref,
        },
        pl_node: struct {
            /// Offset from Decl AST node index.
            /// `Tag` determines which kind of AST node this points to.
            src_node: Ast.Node.Offset,
            /// index into extra.
            /// `Tag` determines what lives there.
            payload_index: u32,
        },
        pl_tok: struct {
            /// Offset from Decl AST token index.
            src_tok: Ast.TokenOffset,
            /// index into extra.
            /// `Tag` determines what lives there.
            payload_index: u32,
        },
        bin: Bin,
        /// For strings which may contain null bytes.
        str: struct {
            /// Offset into `string_bytes`.
            start: NullTerminatedString,
            /// Number of bytes in the string.
            len: u32,

            pub fn get(self: @This(), code: Zir) []const u8 {
                return code.string_bytes[@backingInt(self.start)..][0..self.len];
            }
        },
        str_tok: struct {
            /// Offset into `string_bytes`. Null-terminated.
            start: NullTerminatedString,
            /// Offset from Decl AST token index.
            src_tok: Ast.TokenOffset,

            pub fn get(self: @This(), code: Zir) [:0]const u8 {
                return code.nullTerminatedString(self.start);
            }
        },
        /// Offset from Decl AST token index.
        tok: Ast.TokenOffset,
        /// Offset from Decl AST node index.
        node: Ast.Node.Offset,
        int: u64,
        float: f64,
        ptr_type: struct {
            flags: packed struct {
                is_allowzero: bool,
                is_mutable: bool,
                is_volatile: bool,
                has_sentinel: bool,
                has_align: bool,
                has_addrspace: bool,
                has_bit_range: bool,
                _: u1 = 0,
            },
            size: std.lang.Type.Pointer.Size,
            /// Index into extra. See `PtrType`.
            payload_index: u32,
        },
        int_type: struct {
            /// Offset from Decl AST node index.
            /// `Tag` determines which kind of AST node this points to.
            src_node: Ast.Node.Offset,
            signedness: std.lang.Signedness,
            bit_count: u16,
        },
        @"unreachable": struct {
            /// Offset from Decl AST node index.
            /// `Tag` determines which kind of AST node this points to.
            src_node: Ast.Node.Offset,
        },
        @"break": struct {
            operand: Ref,
            /// Index of a `Break` payload.
            payload_index: u32,
        },
        dbg_stmt: LineColumn,
        /// Used for unary operators which reference an inst,
        /// with an AST node source location.
        inst_node: struct {
            /// Offset from Decl AST node index.
            src_node: Ast.Node.Offset,
            /// The meaning of this operand depends on the corresponding `Tag`.
            inst: Index,
        },
        str_op: struct {
            /// Offset into `string_bytes`. Null-terminated.
            str: NullTerminatedString,
            operand: Ref,

            pub fn getStr(self: @This(), zir: Zir) [:0]const u8 {
                return zir.nullTerminatedString(self.str);
            }
        },
        @"defer": struct {
            index: u32,
            len: u32,
        },
        save_err_ret_index: struct {
            operand: Ref, // If error type (or .none), save new trace index
        },
        elem_val_imm: struct {
            /// The indexable value being accessed.
            operand: Ref,
            /// The index being accessed.
            idx: u32,
        },
        declaration: struct {
            /// This node provides a new absolute baseline node for all instructions within this struct.
            src_node: Ast.Node.Index,
            /// index into extra to a `Declaration` payload.
            payload_index: u32,
        },

        // Make sure we don't accidentally add a field to make this union
        // bigger than expected. Note that in Debug builds, Zig is allowed
        // to insert a secret field for safety checks.
        comptime {
            if (builtin.mode != .debug and builtin.mode != .safe) {
                assert(@sizeOf(Data) == 8);
            }
        }

        /// TODO this has to be kept in sync with `Data` which we want to be an untagged
        /// union. There is some kind of language awkwardness here and it has to do with
        /// deserializing an untagged union (in this case `Data`) from a file, and trying
        /// to preserve the hidden safety field.
        pub const FieldEnum = enum {
            extended,
            un_node,
            un_tok,
            pl_node,
            pl_tok,
            bin,
            str,
            str_tok,
            tok,
            node,
            int,
            float,
            ptr_type,
            int_type,
            @"unreachable",
            @"break",
            dbg_stmt,
            inst_node,
            str_op,
            @"defer",
            save_err_ret_index,
            elem_val_imm,
            declaration,
        };
    };

    pub const Break = struct {
        operand_src_node: Ast.Node.OptionalOffset,
        block_inst: Index,
    };

    /// Trailing:
    /// 0. Output for every outputs_len
    /// 1. Input for every inputs_len
    pub const Asm = struct {
        src_node: Ast.Node.Offset,
        // null-terminated string index
        asm_source: NullTerminatedString,
        /// 1 bit for each outputs_len: whether it uses `-> T` or not.
        ///   0b0 - operand is a pointer to where to store the output.
        ///   0b1 - operand is a type; asm expression has the output as the result.
        /// 0b0X is the first output, 0bX0 is the second, etc.
        output_type_bits: u32,
        clobbers: Ref,

        pub const Small = packed struct(u16) {
            is_volatile: bool,
            outputs_len: u7,
            inputs_len: u8,
        };

        pub const Output = struct {
            /// index into string_bytes (null terminated)
            name: NullTerminatedString,
            /// index into string_bytes (null terminated)
            constraint: NullTerminatedString,
            /// How to interpret this is determined by `output_type_bits`.
            operand: Ref,
        };

        pub const Input = struct {
            /// index into string_bytes (null terminated)
            name: NullTerminatedString,
            /// index into string_bytes (null terminated)
            constraint: NullTerminatedString,
            operand: Ref,
        };
    };

    /// Trailing:
    /// if (ret_ty.body_len == 1) {
    ///   0. return_type: Ref
    /// }
    /// if (ret_ty.body_len > 1) {
    ///   1. return_type: Index // for each ret_ty.body_len
    /// }
    /// 2. body: Index // for each body_len
    /// 3. src_locs: SrcLocs // if body_len != 0
    /// 4. proto_hash: std.zig.SrcHash // if body_len != 0; hash of function prototype
    pub const Func = struct {
        ret_ty: RetTy,
        /// Points to the block that contains the param instructions for this function.
        /// If this is a `declaration`, it refers to the declaration's value body.
        param_block: Index,
        body_len: u32,

        pub const RetTy = packed struct(u32) {
            /// 0 means `void`.
            /// 1 means the type is a simple `Ref`.
            /// Otherwise, the length of a trailing body.
            body_len: u31,
            /// Whether the return type is generic, i.e. refers to one or more previous parameters.
            is_generic: bool,
        };

        pub const SrcLocs = struct {
            /// Line index in the source file relative to the parent decl.
            lbrace_line: u32,
            /// Line index in the source file relative to the parent decl.
            rbrace_line: u32,
            /// lbrace_column is least significant bits u16
            /// rbrace_column is most significant bits u16
            columns: u32,
        };
    };

    /// Trailing:
    /// if (has_cc_ref and !has_cc_body) {
    ///   0. cc: Ref,
    /// }
    /// if (has_cc_body) {
    ///   1. cc_body_len: u32
    ///   2. cc_body: u32 // for each cc_body_len
    /// }
    /// if (has_ret_ty_ref and !has_ret_ty_body) {
    ///   3. ret_ty: Ref,
    /// }
    /// if (has_ret_ty_body) {
    ///   4. ret_ty_body_len: u32
    ///   5. ret_ty_body: u32 // for each ret_ty_body_len
    /// }
    /// 6. noalias_bits: u32 // if has_any_noalias
    ///    - each bit starting with LSB corresponds to parameter indexes
    /// 7. body: Index // for each body_len
    /// 8. src_locs: Func.SrcLocs // if body_len != 0
    /// 9. proto_hash: std.zig.SrcHash // if body_len != 0; hash of function prototype
    pub const FuncFancy = struct {
        /// Points to the block that contains the param instructions for this function.
        /// If this is a `declaration`, it refers to the declaration's value body.
        param_block: Index,
        body_len: u32,
        bits: Bits,

        /// If both has_cc_ref and has_cc_body are false, it means auto calling convention.
        /// If both has_ret_ty_ref and has_ret_ty_body are false, it means void return type.
        pub const Bits = packed struct(u32) {
            is_var_args: bool,
            is_inferred_error: bool,
            is_noinline: bool,
            has_cc_ref: bool,
            has_cc_body: bool,
            has_ret_ty_ref: bool,
            has_ret_ty_body: bool,
            has_any_noalias: bool,
            ret_ty_is_generic: bool,
            _: u23 = 0,
        };
    };

    /// This data is stored inside extra, with trailing operands according to `operands_len`.
    /// Each operand is a `Ref`.
    pub const MultiOp = struct {
        operands_len: u32,
    };

    /// Trailing: operand: Ref, // for each `operands_len` (stored in `small`).
    pub const NodeMultiOp = struct {
        src_node: Ast.Node.Offset,
    };

    /// This data is stored inside extra, with trailing operands according to `body_len`.
    /// Each operand is an `Index`.
    pub const Block = struct {
        body_len: u32,
    };

    /// Trailing:
    /// * inst: Index // for each `body_len`
    pub const BlockComptime = struct {
        reason: std.zig.SimpleComptimeReason,
        body_len: u32,
    };

    /// Trailing:
    /// * inst: Index // for each `body_len`
    pub const BoolBr = struct {
        lhs: Ref,
        body_len: u32,
    };

    /// Trailing:
    /// 0. name: NullTerminatedString      // if `flags.id.hasName()`
    /// 1. lib_name: NullTerminatedString  // if `flags.id.hasLibName()`
    /// 2. type_body_len: u32              // if `flags.id.hasTypeBody()`
    /// 3. align_body_len: u32             // if `flags.id.hasSpecialBodies()`
    /// 4. linksection_body_len: u32       // if `flags.id.hasSpecialBodies()`
    /// 5. addrspace_body_len: u32         // if `flags.id.hasSpecialBodies()`
    /// 6. value_body_len: u32             // if `flags.id.hasValueBody()`
    /// 7. type_body_inst: Zir.Inst.Index
    ///    - for each `type_body_len`
    ///    - body to be exited via `break_inline` to this `declaration` instruction
    /// 8. align_body_inst: Zir.Inst.Index
    ///    - for each `align_body_len`
    ///    - body to be exited via `break_inline` to this `declaration` instruction
    /// 9. linksection_body_inst: Zir.Inst.Index
    ///    - for each `linksection_body_len`
    ///    - body to be exited via `break_inline` to this `declaration` instruction
    /// 10. addrspace_body_inst: Zir.Inst.Index
    ///    - for each `addrspace_body_len`
    ///    - body to be exited via `break_inline` to this `declaration` instruction
    /// 11. value_body_inst: Zir.Inst.Index
    ///    - for each `value_body_len`
    ///    - body to be exited via `break_inline` to this `declaration` instruction
    ///    - within this body, the `declaration` instruction refers to the resolved type from the type body
    pub const Declaration = struct {
        // These fields should be concatenated and reinterpreted as a `std.zig.SrcHash`.
        src_hash_0: u32,
        src_hash_1: u32,
        src_hash_2: u32,
        src_hash_3: u32,
        // These fields should be concatenated and reinterpreted as a `Flags`.
        flags_0: u32,
        flags_1: u32,

        pub const Unwrapped = struct {
            pub const Kind = enum {
                unnamed_test,
                @"test",
                decltest,
                @"comptime",
                @"const",
                @"var",
            };

            pub const Linkage = enum {
                normal,
                @"extern",
                @"export",
            };

            src_node: Ast.Node.Index,

            src_line: u32,
            src_column: u32,

            kind: Kind,
            /// Always `.empty` for `kind` of `unnamed_test`, `.@"comptime"`
            name: NullTerminatedString,
            /// Always `false` for `kind` of `unnamed_test`, `.@"test"`, `.decltest`, `.@"comptime"`.
            is_pub: bool,
            /// Always `false` for `kind != .@"var"`.
            is_threadlocal: bool,
            /// Always `.normal` for `kind != .@"const" and kind != .@"var"`.
            linkage: Linkage,
            /// Always `.empty` for `linkage != .@"extern"`.
            lib_name: NullTerminatedString,

            /// Always populated for `linkage == .@"extern".
            type_body: ?[]const Inst.Index,
            align_body: ?[]const Inst.Index,
            linksection_body: ?[]const Inst.Index,
            addrspace_body: ?[]const Inst.Index,
            /// Always populated for `linkage != .@"extern".
            value_body: ?[]const Inst.Index,
        };

        pub const Flags = packed struct(u64) {
            src_line: u30,
            src_column: u29,
            id: Id,

            pub const Id = enum(u5) {
                unnamed_test,
                @"test",
                decltest,
                @"comptime",

                const_simple,
                const_typed,
                @"const",
                pub_const_simple,
                pub_const_typed,
                pub_const,

                extern_const_simple,
                extern_const,
                pub_extern_const_simple,
                pub_extern_const,

                export_const,
                pub_export_const,

                var_simple,
                @"var",
                var_threadlocal,
                pub_var_simple,
                pub_var,
                pub_var_threadlocal,

                extern_var,
                extern_var_threadlocal,
                pub_extern_var,
                pub_extern_var_threadlocal,

                export_var,
                export_var_threadlocal,
                pub_export_var,
                pub_export_var_threadlocal,

                pub fn hasName(id: Id) bool {
                    return switch (id) {
                        .unnamed_test,
                        .@"comptime",
                        => false,
                        else => true,
                    };
                }

                pub fn hasLibName(id: Id) bool {
                    return switch (id) {
                        .extern_const,
                        .pub_extern_const,
                        .extern_var,
                        .extern_var_threadlocal,
                        .pub_extern_var,
                        .pub_extern_var_threadlocal,
                        => true,
                        else => false,
                    };
                }

                pub fn hasTypeBody(id: Id) bool {
                    return switch (id) {
                        .unnamed_test,
                        .@"test",
                        .decltest,
                        .@"comptime",
                        => false, // these constructs are untyped
                        .const_simple,
                        .pub_const_simple,
                        .var_simple,
                        .pub_var_simple,
                        => false, // these reprs omit type bodies
                        else => true,
                    };
                }

                pub fn hasValueBody(id: Id) bool {
                    return switch (id) {
                        .extern_const_simple,
                        .extern_const,
                        .pub_extern_const_simple,
                        .pub_extern_const,
                        .extern_var,
                        .extern_var_threadlocal,
                        .pub_extern_var,
                        .pub_extern_var_threadlocal,
                        => false, // externs do not have values
                        else => true,
                    };
                }

                pub fn hasSpecialBodies(id: Id) bool {
                    return switch (id) {
                        .unnamed_test,
                        .@"test",
                        .decltest,
                        .@"comptime",
                        => false, // these constructs are untyped
                        .const_simple,
                        .const_typed,
                        .pub_const_simple,
                        .pub_const_typed,
                        .extern_const_simple,
                        .pub_extern_const_simple,
                        .var_simple,
                        .pub_var_simple,
                        => false, // these reprs omit special bodies
                        else => true,
                    };
                }

                pub fn linkage(id: Id) Declaration.Unwrapped.Linkage {
                    return switch (id) {
                        .extern_const_simple,
                        .extern_const,
                        .pub_extern_const_simple,
                        .pub_extern_const,
                        .extern_var,
                        .extern_var_threadlocal,
                        .pub_extern_var,
                        .pub_extern_var_threadlocal,
                        => .@"extern",
                        .export_const,
                        .pub_export_const,
                        .export_var,
                        .export_var_threadlocal,
                        .pub_export_var,
                        .pub_export_var_threadlocal,
                        => .@"export",
                        else => .normal,
                    };
                }

                pub fn kind(id: Id) Declaration.Unwrapped.Kind {
                    return switch (id) {
                        .unnamed_test => .unnamed_test,
                        .@"test" => .@"test",
                        .decltest => .decltest,
                        .@"comptime" => .@"comptime",
                        .const_simple,
                        .const_typed,
                        .@"const",
                        .pub_const_simple,
                        .pub_const_typed,
                        .pub_const,
                        .extern_const_simple,
                        .extern_const,
                        .pub_extern_const_simple,
                        .pub_extern_const,
                        .export_const,
                        .pub_export_const,
                        => .@"const",
                        .var_simple,
                        .@"var",
                        .var_threadlocal,
                        .pub_var_simple,
                        .pub_var,
                        .pub_var_threadlocal,
                        .extern_var,
                        .extern_var_threadlocal,
                        .pub_extern_var,
                        .pub_extern_var_threadlocal,
                        .export_var,
                        .export_var_threadlocal,
                        .pub_export_var,
                        .pub_export_var_threadlocal,
                        => .@"var",
                    };
                }

                pub fn isPub(id: Id) bool {
                    return switch (id) {
                        .pub_const_simple,
                        .pub_const_typed,
                        .pub_const,
                        .pub_extern_const_simple,
                        .pub_extern_const,
                        .pub_export_const,
                        .pub_var_simple,
                        .pub_var,
                        .pub_var_threadlocal,
                        .pub_extern_var,
                        .pub_extern_var_threadlocal,
                        .pub_export_var,
                        .pub_export_var_threadlocal,
                        => true,
                        else => false,
                    };
                }

                pub fn isThreadlocal(id: Id) bool {
                    return switch (id) {
                        .var_threadlocal,
                        .pub_var_threadlocal,
                        .extern_var_threadlocal,
                        .pub_extern_var_threadlocal,
                        .export_var_threadlocal,
                        .pub_export_var_threadlocal,
                        => true,
                        else => false,
                    };
                }
            };
        };

        pub const Name = enum(u32) {
            @"comptime" = std.math.maxInt(u32),
            unnamed_test = std.math.maxInt(u32) - 1,
            /// Other values are `NullTerminatedString` values, i.e. index into
            /// `string_bytes`. If the byte referenced is 0, the decl is a named
            /// test, and the actual name begins at the following byte.
            _,

            pub fn isNamedTest(name: Name, zir: Zir) bool {
                return switch (name) {
                    .@"comptime", .unnamed_test => false,
                    _ => zir.string_bytes[@backingInt(name)] == 0,
                };
            }
            pub fn toString(name: Name, zir: Zir) ?NullTerminatedString {
                switch (name) {
                    .@"comptime", .unnamed_test => return null,
                    _ => {},
                }
                const idx: u32 = @backingInt(name);
                if (zir.string_bytes[idx] == 0) {
                    // Named test
                    return @fromBackingInt(@intCast(idx + 1));
                }
                return @fromBackingInt(@intCast(idx));
            }
        };

        pub const Bodies = struct {
            type_body: ?[]const Index,
            align_body: ?[]const Index,
            linksection_body: ?[]const Index,
            addrspace_body: ?[]const Index,
            value_body: ?[]const Index,
        };

        pub fn getBodies(declaration: Declaration, extra_end: u32, zir: Zir) Bodies {
            var extra_index: u32 = extra_end;
            const value_body_len = declaration.value_body_len;
            const type_body_len: u32 = len: {
                if (!declaration.flags().kind.hasTypeBody()) break :len 0;
                const len = zir.extra[extra_index];
                extra_index += 1;
                break :len len;
            };
            const align_body_len, const linksection_body_len, const addrspace_body_len = lens: {
                if (!declaration.flags.kind.hasSpecialBodies()) {
                    break :lens .{ 0, 0, 0 };
                }
                const lens = zir.extra[extra_index..][0..3].*;
                extra_index += 3;
                break :lens lens;
            };
            return .{
                .type_body = if (type_body_len == 0) null else b: {
                    const b = zir.bodySlice(extra_index, type_body_len);
                    extra_index += type_body_len;
                    break :b b;
                },
                .align_body = if (align_body_len == 0) null else b: {
                    const b = zir.bodySlice(extra_index, align_body_len);
                    extra_index += align_body_len;
                    break :b b;
                },
                .linksection_body = if (linksection_body_len == 0) null else b: {
                    const b = zir.bodySlice(extra_index, linksection_body_len);
                    extra_index += linksection_body_len;
                    break :b b;
                },
                .addrspace_body = if (addrspace_body_len == 0) null else b: {
                    const b = zir.bodySlice(extra_index, addrspace_body_len);
                    extra_index += addrspace_body_len;
                    break :b b;
                },
                .value_body = if (value_body_len == 0) null else b: {
                    const b = zir.bodySlice(extra_index, value_body_len);
                    extra_index += value_body_len;
                    break :b b;
                },
            };
        }
    };

    /// Stored inside extra, with trailing arguments according to `args_len`.
    /// Implicit 0. arg_0_start: u32, // always same as `args_len`
    /// 1. arg_end: u32, // for each `args_len`
    /// arg_N_start is the same as arg_N-1_end
    pub const Call = struct {
        // Note: Flags *must* come first so that unusedResultExpr
        // can find it when it goes to modify them.
        flags: Flags,
        callee: Ref,

        pub const Flags = packed struct {
            /// std.lang.CallModifier in packed form
            pub const PackedModifier = u3;
            pub const PackedArgsLen = u27;

            packed_modifier: PackedModifier,
            ensure_result_used: bool = false,
            pop_error_return_trace: bool,
            args_len: PackedArgsLen,

            comptime {
                if (@sizeOf(Flags) != 4 or @bitSizeOf(Flags) != 32)
                    @compileError("Layout of Call.Flags needs to be updated!");
                if (@bitSizeOf(std.lang.CallModifier) != @bitSizeOf(PackedModifier))
                    @compileError("Call.Flags.PackedModifier needs to be updated!");
            }
        };
    };

    /// Stored inside extra, with trailing arguments according to `args_len`.
    /// Implicit 0. arg_0_start: u32, // always same as `args_len`
    /// 1. arg_end: u32, // for each `args_len`
    /// arg_N_start is the same as arg_N-1_end
    pub const FieldCall = struct {
        // Note: Flags *must* come first so that unusedResultExpr
        // can find it when it goes to modify them.
        flags: Call.Flags,
        obj_ptr: Ref,
        /// Offset into `string_bytes`.
        field_name_start: NullTerminatedString,
    };

    /// There is a body of instructions at `extra[body_index..][0..body_len]`.
    /// Trailing:
    /// 0. operand: Ref // for each `operands_len`
    pub const TypeOfPeer = struct {
        src_node: Ast.Node.Offset,
        body_len: u32,
        body_index: u32,
    };

    pub const BuiltinCall = struct {
        // Note: Flags *must* come first so that unusedResultExpr
        // can find it when it goes to modify them.
        flags: Flags,
        modifier: Ref,
        callee: Ref,
        args: Ref,

        pub const Flags = packed struct {
            is_nosuspend: bool,
            ensure_result_used: bool,
            _: u30 = 0,

            comptime {
                if (@sizeOf(Flags) != 4 or @bitSizeOf(Flags) != 32)
                    @compileError("Layout of BuiltinCall.Flags needs to be updated!");
            }
        };
    };

    /// This data is stored inside extra, with two sets of trailing `Ref`:
    /// * 0. the then body, according to `then_body_len`.
    /// * 1. the else body, according to `else_body_len`.
    pub const CondBr = struct {
        condition: Ref,
        then_body_len: u32,
        else_body_len: u32,
    };

    /// This data is stored inside extra, trailed by:
    /// * 0. body: Index //  for each `body_len`.
    pub const Try = struct {
        /// The error union to unwrap.
        operand: Ref,
        body_len: u32,
    };

    /// Stored in extra. Depending on the flags in Data, there will be up to 5
    /// trailing Ref fields:
    /// 0. sentinel: Ref // if `has_sentinel` flag is set
    /// 1. align: Ref // if `has_align` flag is set
    /// 2. address_space: Ref // if `has_addrspace` flag is set
    /// 3. bit_start: Ref // if `has_bit_range` flag is set
    /// 4. host_size: Ref // if `has_bit_range` flag is set
    pub const PtrType = struct {
        elem_type: Ref,
        src_node: Ast.Node.Offset,
    };

    pub const ArrayTypeSentinel = struct {
        len: Ref,
        sentinel: Ref,
        elem_type: Ref,
    };

    pub const SliceStart = struct {
        lhs: Ref,
        start: Ref,
    };

    pub const SliceEnd = struct {
        lhs: Ref,
        start: Ref,
        end: Ref,
    };

    pub const SliceSentinel = struct {
        lhs: Ref,
        start: Ref,
        end: Ref,
        sentinel: Ref,
    };

    pub const SliceLength = struct {
        lhs: Ref,
        start: Ref,
        len: Ref,
        sentinel: Ref,
        start_src_node_offset: Ast.Node.Offset,
    };

    /// The meaning of these operands depends on the corresponding `Tag`.
    pub const Bin = struct {
        lhs: Ref,
        rhs: Ref,
    };

    pub const BinNode = struct {
        node: Ast.Node.Offset,
        lhs: Ref,
        rhs: Ref,
    };

    pub const ReifySliceArgInfo = enum(u16) {
        /// Input element type is `type`.
        /// Output element type is `std.lang.Type.Fn.ParamAttributes`.
        type_to_fn_param_attrs,
        /// Input element type is `[]const u8`.
        /// Output element type is `type`.
        string_to_struct_field_type,
        /// Identical to `string_to_struct_field_type` aside from emitting slightly different error messages.
        string_to_union_field_type,
        /// Input element type is `[]const u8`.
        /// Output element type is `std.lang.Type.Struct.FieldAttributes`.
        string_to_struct_field_attrs,
        /// Input element type is `[]const u8`.
        /// Output element type is `std.lang.Type.Union.FieldAttributes`.
        string_to_union_field_attrs,
    };

    pub const RoundOp = enum(u16) {
        round,
        floor,
        ceil,
        trunc,
    };

    pub const UnNode = struct {
        node: Ast.Node.Offset,
        operand: Ref,
    };

    pub const ElemPtrImm = struct {
        ptr: Ref,
        index: u32,
    };

    pub const ReifyPointer = struct {
        node: Ast.Node.Offset,
        size: Ref,
        attrs: Ref,
        elem_ty: Ref,
        sentinel: Ref,
    };

    pub const ReifyFn = struct {
        node: Ast.Node.Offset,
        param_types: Ref,
        param_attrs: Ref,
        ret_ty: Ref,
        fn_attrs: Ref,
    };

    pub const ReifyStruct = struct {
        src_line: u32,
        /// This node is absolute, because `reify` instructions are tracked across updates, and
        /// this simplifies the logic for getting source locations for types.
        node: Ast.Node.Index,
        layout: Ref,
        backing_ty: Ref,
        field_names: Ref,
        field_types: Ref,
        field_attrs: Ref,
    };

    pub const ReifyUnion = struct {
        src_line: u32,
        /// This node is absolute, because `reify` instructions are tracked across updates, and
        /// this simplifies the logic for getting source locations for types.
        node: Ast.Node.Index,
        layout: Ref,
        arg_ty: Ref,
        field_names: Ref,
        field_types: Ref,
        field_attrs: Ref,
    };

    pub const ReifyEnum = struct {
        src_line: u32,
        /// This node is absolute, because `reify` instructions are tracked across updates, and
        /// this simplifies the logic for getting source locations for types.
        node: Ast.Node.Index,
        tag_ty: Ref,
        mode: Ref,
        field_names: Ref,
        field_values: Ref,
    };

    pub const ReifySpirvType = struct {
        src_line: u32,
        /// This node is absolute, because `reify` instructions are tracked across updates, and
        /// this simplifies the logic for getting source locations for types.
        node: Ast.Node.Index,
        operand: Ref,
    };

    /// Trailing:
    /// 0. multi_cases_len: u32, // If has_multi_cases is set.
    /// 1. payload_capture_placeholder: Inst.Index, // If payload_capture_inst_is_placeholder is set.
    ///                                             // Index of instruction prongs use to refer to their payload capture.
    /// 2. tag_capture_placeholder: Inst.Index, // If tag_capture_inst_is_placeholder is set.
    ///                                         // Index of instruction prongs use to refer to their tag capture.
    /// 3. catch_or_if_src_node_offset: Ast.Node.Offset, // If inst is switch_block_err_union.
    /// 4. non_err_info: ProngInfo.NonErr, // If inst is switch_block_err_union.
    /// 5. else_info: ProngInfo.Else, // If has_else is set.
    /// 6. scalar_prong_info: ProngInfo, // for every scalar_cases_len
    /// 7. multi_prong_info: ProngInfo, // for every multi_cases_len
    /// 8. multi_case_items_len: u32, // for every multi_cases_len
    /// 9. multi_case_ranges_len: u32, // If has_ranges is set: for every multi_cases_len
    /// 10. scalar_item_info: ItemInfo, // for every scalar_cases_len
    /// 11. multi_items_info: { // for every multi_cases_len
    ///        item_info: ItemInfo, // for each multi_case_items_len
    ///        range_items_info: { // for each multi_case_ranges_len
    ///            first_info: ItemInfo,
    ///            last_info: ItemInfo,
    ///        }
    ///    }
    /// 12. non_err_body {
    ///        body_inst: Index // for every non_err_info.body_len
    ///     }
    /// 13. else_body: { // If has_else is set.
    ///        body_inst: Inst.Index, // for every else_info.body_len
    ///    }
    /// 14. scalar_bodies: { // for every scalar_cases_len
    ///        prong_body: { // for each body_len in scalar_prong_info
    ///            body_inst: Inst.Index, // for every body_len
    ///        }
    ///        item_body: { // for each body_len in scalar_item_info
    ///            body_inst: Inst.Index, // for every body_len
    ///        }
    ///    }
    /// 15. multi_bodies: { // for each multi_items_info
    ///        prong_body: {
    ///            body_inst: Inst.Index, // for each multi_prong_info.body_len
    ///        }
    ///        item_body: { // for each item_info
    ///            body_inst: Inst.Index, // for every item_info.body_len
    ///        }
    ///        range_bodies: { // for each .{first_info, last_info} in range_items_info
    ///            first_body_inst: Inst.Index, // for every first_info.body_len
    ///            last_body_inst: Inst.Index, // for every last_info.body_len
    ///        }
    ///    }
    pub const SwitchBlock = struct {
        /// Either `catch`/`if` or `switch` operand.
        raw_operand: Ref,
        bits: Bits,

        pub const Bits = packed struct(u32) {
            /// If true, one or more prongs have multiple items.
            has_multi_cases: bool,
            /// If true, one or more prongs have ranges.
            /// Only valid if `has_multi_cases` is also set.
            any_ranges: bool,
            has_else: bool,
            has_under: bool,
            /// If true, at least one prong contains a `continue`.
            /// Only valid if `has_label` is set.
            has_continue: bool,
            // If true, at least one prong has a non-inline payload/tag capture.
            any_maybe_runtime_capture: bool,
            payload_capture_inst_is_placeholder: bool,
            tag_capture_inst_is_placeholder: bool,
            scalar_cases_len: ScalarCasesLen,

            // NOTE maybe don't steal any more bits from poor `scalar_cases_len`
            // and split `Bits` into two parts instead, `raw_operand` surely
            // wouldn't mind donating a couple of bits for that purpose...
            pub const ScalarCasesLen = u24;
        };

        pub const ProngInfo = packed struct(u32) {
            body_len: u27,
            capture: ProngInfo.Capture,
            is_inline: bool,
            has_tag_capture: bool,
            is_comptime_unreach: bool,

            pub const Capture = enum(u2) {
                none,
                by_val,
                by_ref,
            };

            pub const NonErr = packed struct(u32) {
                body_len: u29,
                capture: ProngInfo.Capture,
                operand_is_ref: bool,
            };

            pub const Else = packed struct(u32) {
                body_len: u27,
                capture: ProngInfo.Capture,
                is_inline: bool,
                has_tag_capture: bool,
                is_simple_noreturn: bool,
            };
        };

        pub const ItemInfo = packed struct(u32) {
            kind: ItemInfo.Kind,
            data: u30,

            pub const Kind = enum(u2) {
                enum_literal,
                error_value,
                body_len,
                under,
            };

            pub const Unwrapped = union(ItemInfo.Kind) {
                enum_literal: Zir.NullTerminatedString,
                error_value: Zir.NullTerminatedString,
                body_len: u32,
                under,
            };

            pub fn wrap(unwrapped: ItemInfo.Unwrapped) ItemInfo {
                const data_uncasted: u32 = switch (unwrapped) {
                    .enum_literal => |str_index| @backingInt(str_index),
                    .error_value => |str_index| @backingInt(str_index),
                    .body_len => |body_len| body_len,
                    .under => 0,
                };
                return .{ .kind = unwrapped, .data = @intCast(data_uncasted) };
            }

            pub fn unwrap(item_info: ItemInfo) ItemInfo.Unwrapped {
                return switch (item_info.kind) {
                    .enum_literal => .{ .enum_literal = @fromBackingInt(@intCast(item_info.data)) },
                    .error_value => .{ .error_value = @fromBackingInt(@intCast(item_info.data)) },
                    .body_len => .{ .body_len = item_info.data },
                    .under => .under,
                };
            }

            pub fn bodyLen(item_info: ItemInfo) ?u32 {
                return if (item_info.kind == .body_len) item_info.data else null;
            }
        };
    };

    pub const ArrayInitRefTy = struct {
        ptr_ty: Ref,
        elem_count: u32,
    };

    pub const Field = struct {
        lhs: Ref,
        /// Offset into `string_bytes`.
        field_name_start: NullTerminatedString,
    };

    pub const FieldNamed = struct {
        lhs: Ref,
        field_name: Ref,
    };

    pub const As = struct {
        dest_type: Ref,
        operand: Ref,
    };

    /// Trailing:
    /// 0.  captures_len: u32 // if `has_captures_len`
    /// 1.  decls_len: u32, // if `has_decls_len`
    /// 2.  fields_len: u32, // if `has_fields_len`
    /// 3.  backing_int_body_len: u32 // if `has_backing_int`
    /// 4.  capture: Capture // for every `captures_len`
    /// 5.  capture_name: NullTerminatedString // for every `captures_len`
    /// 6.  decl: Index, // for every `decls_len`; points to a `declaration` instruction
    /// 7.  field_name: NullTerminatedString // for every `fields_len`
    /// 8.  field_type_body_len: u32 // for every `fields_len`
    /// 9.  field_align_body_len: u32 // for every `fields_len` if `any_field_aligns`
    /// 10. field_default_body_len: u32 // for every `fields_len` if `any_field_defaults`
    /// 11. field_comptime_bits: u32 // one bit per `fields_len` if `any_comptime_fields`
    ///                              // LSB is first field, minimum number of `u32` needed
    /// 12. backing_int_body_inst: Inst.Index // for each `backing_int_body_len`
    /// 13. body_inst: Inst.Index // type body, then align body, then default body, for each field
    pub const StructDecl = struct {
        // These fields should be concatenated and reinterpreted as a `std.zig.SrcHash`.
        // This hash contains the source of all fields, and any specified attributes (`extern`, backing type, etc).
        fields_hash_0: u32,
        fields_hash_1: u32,
        fields_hash_2: u32,
        fields_hash_3: u32,
        src_line: u32,
        /// This node provides a new absolute baseline node for all instructions within this struct.
        src_node: Ast.Node.Index,

        pub const Small = packed struct(u16) {
            has_captures_len: bool,
            has_decls_len: bool,
            has_fields_len: bool,
            name_strategy: NameStrategy,
            layout: std.lang.Type.ContainerLayout,
            /// Always `false` if `layout != .@"packed"`.
            has_backing_int_type: bool,
            any_field_aligns: bool,
            any_field_defaults: bool,
            any_comptime_fields: bool,
            _: u5 = 0,
        };
    };

    /// Represents a single value being captured in a type declaration's closure.
    pub const Capture = packed struct(u32) {
        tag: enum(u3) {
            /// `data` is a `u16` index into the parent closure.
            nested,
            /// `data` is a `Zir.Inst.Index` to an instruction whose value is being captured.
            instruction,
            /// `data` is a `Zir.Inst.Index` to an instruction representing an alloc whose contents is being captured.
            instruction_load,
            /// `data` is a `NullTerminatedString` to a decl name.
            decl_val,
            /// `data` is a `NullTerminatedString` to a decl name.
            decl_ref,
        },
        data: u29,
        pub const Unwrapped = union(enum) {
            nested: u16,
            instruction: Zir.Inst.Index,
            instruction_load: Zir.Inst.Index,
            decl_val: NullTerminatedString,
            decl_ref: NullTerminatedString,
        };
        pub fn wrap(cap: Unwrapped) Capture {
            return switch (cap) {
                .nested => |idx| .{
                    .tag = .nested,
                    .data = idx,
                },
                .instruction => |inst| .{
                    .tag = .instruction,
                    .data = @intCast(@backingInt(inst)),
                },
                .instruction_load => |inst| .{
                    .tag = .instruction_load,
                    .data = @intCast(@backingInt(inst)),
                },
                .decl_val => |str| .{
                    .tag = .decl_val,
                    .data = @intCast(@backingInt(str)),
                },
                .decl_ref => |str| .{
                    .tag = .decl_ref,
                    .data = @intCast(@backingInt(str)),
                },
            };
        }
        pub fn unwrap(cap: Capture) Unwrapped {
            return switch (cap.tag) {
                .nested => .{ .nested = @intCast(cap.data) },
                .instruction => .{ .instruction = @fromBackingInt(@intCast(cap.data)) },
                .instruction_load => .{ .instruction_load = @fromBackingInt(@intCast(cap.data)) },
                .decl_val => .{ .decl_val = @fromBackingInt(@intCast(cap.data)) },
                .decl_ref => .{ .decl_ref = @fromBackingInt(@intCast(cap.data)) },
            };
        }
    };

    pub const NameStrategy = enum(u2) {
        /// Use the same name as the parent declaration name.
        /// e.g. `const Foo = struct {...};`.
        parent,
        /// Use the name of the currently executing comptime function call,
        /// with the current parameters. e.g. `ArrayList(i32)`.
        func,
        /// Create an anonymous name for this declaration.
        /// Like this: "ParentDeclName_struct_69"
        anon,
        /// Use the name specified in the next `dbg_var_{val,ptr}` instruction.
        dbg_var,
    };

    pub const FullPtrCastFlags = packed struct(u5) {
        ptr_cast: bool = false,
        align_cast: bool = false,
        addrspace_cast: bool = false,
        const_cast: bool = false,
        volatile_cast: bool = false,

        pub inline fn needResultTypeBuiltinName(flags: FullPtrCastFlags) []const u8 {
            if (flags.ptr_cast) return "@ptrCast";
            if (flags.align_cast) return "@alignCast";
            if (flags.addrspace_cast) return "@addrSpaceCast";
            unreachable;
        }
    };

    pub const StdLangValue = enum(u16) {
        // Types
        atomic_order,
        atomic_rmw_op,
        calling_convention,
        address_space,
        float_mode,
        signedness,
        reduce_op,
        call_modifier,
        prefetch_options,
        export_options,
        extern_options,
        branch_hint,
        clobbers,
        pointer_size,
        pointer_attributes,
        fn_attributes,
        container_layout,
        enum_mode,
        spirv_type_options,
        // Values
        calling_convention_c,
        calling_convention_inline,
    };

    pub const InplaceOp = enum(u16) {
        add_eq,
        sub_eq,
    };

    /// Trailing:
    /// 0. captures_len: u32, // if has_captures_len
    /// 1. decls_len: u32, // if has_decls_len
    /// 2. fields_len: u32, // if has_fields_len
    /// 3. tag_type_body_len: u32, // if has_tag_type
    /// 4. capture: Capture // for every `captures_len`
    /// 5. capture_name: NullTerminatedString // for every `captures_len`
    /// 6. decl: Index, // for every `decls_len`; points to a `declaration` instruction
    /// 7. field_name: NullTerminatedString // for every `fields_len`
    /// 8. field_value_body_len: u32 // for every `fields_len` if `any_field_values`
    /// 9. tag_type_body_inst: Inst.Index // for each `tag_type_body_len`
    /// 10. body_inst: Inst.Index // value body for each field
    pub const EnumDecl = struct {
        // These fields should be concatenated and reinterpreted as a `std.zig.SrcHash`.
        // This hash contains the source of all fields, and the backing type if specified.
        fields_hash_0: u32,
        fields_hash_1: u32,
        fields_hash_2: u32,
        fields_hash_3: u32,
        src_line: u32,
        /// This node provides a new absolute baseline node for all instructions within this struct.
        src_node: Ast.Node.Index,

        pub const Small = packed struct(u16) {
            has_captures_len: bool,
            has_decls_len: bool,
            has_fields_len: bool,
            name_strategy: NameStrategy,
            has_tag_type: bool,
            nonexhaustive: bool,
            any_field_values: bool,
            _: u8 = 0,
        };
    };

    /// Trailing:
    /// 0.  captures_len: u32 // if `has_captures_len`
    /// 1.  decls_len: u32, // if `has_decls_len`
    /// 2.  fields_len: u32, // if `has_fields_len`
    /// 3.  arg_type_body_len: u32, // if `kind.hasArgType()`
    /// 4.  capture: Capture // for every `captures_len`
    /// 5.  capture_name: NullTerminatedString // for every `captures_len`
    /// 6.  decl: Index, // for every `decls_len`; points to a `declaration` instruction
    /// 7.  field_name: NullTerminatedString // for every `fields_len`
    /// 8.  field_type_body_len: u32 // for every `fields_len`
    /// 9 . field_align_body_len: u32 // for every `fields_len` if `any_field_aligns`
    /// 10. field_value_body_len: u32 // for every `fields_len` if `any_field_values`
    /// 11. arg_type_body_inst: Inst.Index // for each `arg_type_body_len`
    /// 12. body_inst: Inst.Index // type body, then align body, then value body, for each field
    pub const UnionDecl = struct {
        // These fields should be concatenated and reinterpreted as a `std.zig.SrcHash`.
        // This hash contains the source of all fields, and any specified attributes (`extern` etc).
        fields_hash_0: u32,
        fields_hash_1: u32,
        fields_hash_2: u32,
        fields_hash_3: u32,
        src_line: u32,
        /// This node provides a new absolute baseline node for all instructions within this struct.
        src_node: Ast.Node.Index,

        pub const Small = packed struct(u16) {
            has_captures_len: bool,
            has_decls_len: bool,
            has_fields_len: bool,
            name_strategy: NameStrategy,
            kind: Kind,
            any_field_aligns: bool,
            any_field_values: bool,
            _: u6 = 0,
        };

        pub const Kind = enum(u3) {
            /// `union`
            auto,
            /// `union(T)`
            tagged_explicit,
            /// `union(enum)`
            tagged_enum,
            /// `union(enum(T))`
            tagged_enum_explicit,
            /// `extern union`
            @"extern",
            /// `packed union`
            @"packed",
            /// `packed union(T)`
            packed_explicit,

            pub fn hasArgType(k: Kind) bool {
                return switch (k) {
                    .auto, .tagged_enum, .@"extern", .@"packed" => false,
                    .tagged_explicit, .tagged_enum_explicit, .packed_explicit => true,
                };
            }

            pub fn layout(k: Kind) std.lang.Type.ContainerLayout {
                return switch (k) {
                    .auto, .tagged_explicit, .tagged_enum, .tagged_enum_explicit => .auto,
                    .@"extern" => .@"extern",
                    .@"packed", .packed_explicit => .@"packed",
                };
            }
        };
    };

    /// Trailing:
    /// 0. captures_len: u32, // if has_captures_len
    /// 1. decls_len: u32, // if has_decls_len
    /// 2. capture: Capture, // for every captures_len
    /// 3. capture_name: NullTerminatedString // for every captures_len
    /// 4. decl: Index, // for every decls_len; points to a `declaration` instruction
    pub const OpaqueDecl = struct {
        src_line: u32,
        /// This node provides a new absolute baseline node for all instructions within this struct.
        src_node: Ast.Node.Index,

        pub const Small = packed struct(u16) {
            has_captures_len: bool,
            has_decls_len: bool,
            name_strategy: NameStrategy,
            _: u12 = 0,
        };
    };

    /// Trailing:
    /// 1. fields: { // for every `fields_len` (stored in `extended.small`)
    ///        type: Inst.Ref,
    ///        init: Inst.Ref, // `.none` for non-`comptime` fields
    ///    }
    pub const TupleDecl = struct {
        src_node: Ast.Node.Offset,
    };

    /// Trailing:
    /// 0. field_name: NullTerminatedString // for every fields_len
    pub const ErrorSetDecl = struct {
        fields_len: u32,
    };

    /// A f128 value, broken up into 4 u32 parts.
    pub const Float128 = struct {
        piece0: u32,
        piece1: u32,
        piece2: u32,
        piece3: u32,

        pub fn get(self: Float128) f128 {
            const int_bits = @as(u128, self.piece0) |
                (@as(u128, self.piece1) << 32) |
                (@as(u128, self.piece2) << 64) |
                (@as(u128, self.piece3) << 96);
            return @as(f128, @bitCast(int_bits));
        }
    };

    /// Trailing is an item per field.
    pub const StructInit = struct {
        /// If this is an anonymous initialization (the operand is poison), this instruction becomes the owner of a type.
        /// To resolve source locations, we need an absolute source node.
        abs_node: Ast.Node.Index,
        /// Likewise, we need an absolute line number.
        abs_line: u32,
        fields_len: u32,

        pub const Item = struct {
            /// The `struct_init_field_type` ZIR instruction for this field init.
            field_type: Index,
            /// The field init expression to be used as the field value. This value will be coerced
            /// to the field type if not already.
            init: Ref,
        };
    };

    /// Trailing is an Item per field.
    /// TODO make this instead array of inits followed by array of names because
    /// it will be simpler Sema code and better for CPU cache.
    pub const StructInitAnon = struct {
        /// This is an anonymous initialization, meaning this instruction becomes the owner of a type.
        /// To resolve source locations, we need an absolute source node.
        abs_node: Ast.Node.Index,
        /// Likewise, we need an absolute line number.
        abs_line: u32,
        fields_len: u32,

        pub const Item = struct {
            /// Null-terminated string table index.
            field_name: NullTerminatedString,
            /// The field init expression to be used as the field value.
            init: Ref,
        };
    };

    pub const FieldType = struct {
        container_type: Ref,
        /// Offset into `string_bytes`, null terminated.
        name_start: NullTerminatedString,
    };

    pub const FieldTypeRef = struct {
        container_type: Ref,
        field_name: Ref,
    };

    pub const Cmpxchg = struct {
        node: Ast.Node.Offset,
        ptr: Ref,
        expected_value: Ref,
        new_value: Ref,
        success_order: Ref,
        failure_order: Ref,
    };

    pub const AtomicRmw = struct {
        ptr: Ref,
        operation: Ref,
        operand: Ref,
        ordering: Ref,
    };

    pub const UnionInit = struct {
        union_type: Ref,
        field_name: Ref,
        init: Ref,
    };

    pub const AtomicStore = struct {
        ptr: Ref,
        operand: Ref,
        ordering: Ref,
    };

    pub const AtomicLoad = struct {
        elem_type: Ref,
        ptr: Ref,
        ordering: Ref,
    };

    pub const MulAdd = struct {
        mulend1: Ref,
        mulend2: Ref,
        addend: Ref,
    };

    pub const FieldParentPtr = struct {
        src_node: Ast.Node.Offset,
        parent_ptr_type: Ref,
        field_name: Ref,
        field_ptr: Ref,
    };

    pub const Shuffle = struct {
        elem_type: Ref,
        a: Ref,
        b: Ref,
        mask: Ref,
    };

    pub const Select = struct {
        node: Ast.Node.Offset,
        elem_type: Ref,
        pred: Ref,
        a: Ref,
        b: Ref,
    };

    /// Trailing: inst: Index // for every body_len
    pub const Param = struct {
        /// Null-terminated string index.
        name: NullTerminatedString,
        type: Type,

        pub const Type = packed struct(u32) {
            /// The body contains the type of the parameter.
            body_len: u31,
            /// Whether the type is generic, i.e. refers to one or more previous parameters.
            is_generic: bool,
        };
    };

    /// Trailing:
    /// 0. type_inst: Ref,  // if small 0b000X is set
    /// 1. align_inst: Ref, // if small 0b00X0 is set
    pub const AllocExtended = struct {
        src_node: Ast.Node.Offset,

        pub const Small = packed struct(u16) {
            has_type: bool,
            has_align: bool,
            is_const: bool,
            is_comptime: bool,
            _: u12 = 0,
        };
    };

    pub const Export = struct {
        exported: Ref,
        options: Ref,
    };

    /// Trailing: `CompileErrors.Item` for each `items_len`.
    pub const CompileErrors = struct {
        items_len: u32,

        /// Trailing: `note_payload_index: u32` for each `notes_len`.
        /// It's a payload index of another `Item`.
        pub const Item = struct {
            /// null terminated string index
            msg: NullTerminatedString,
            node: Ast.Node.OptionalIndex,
            /// If node is .none then this will be populated.
            token: Ast.OptionalTokenIndex,
            /// Can be used in combination with `token`.
            byte_offset: u32,
            /// 0 or a payload index of a `Block`, each is a payload
            /// index of another `Item`.
            notes: u32,

            pub fn notesLen(item: Item, zir: Zir) u32 {
                if (item.notes == 0) return 0;
                const block = zir.extraData(Block, item.notes);
                return block.data.body_len;
            }
        };
    };

    /// Trailing: for each `imports_len` there is an Item
    pub const Imports = struct {
        imports_len: u32,

        pub const Item = struct {
            /// null terminated string index
            name: NullTerminatedString,
            /// points to the import name
            token: Ast.TokenIndex,
        };
    };

    pub const LineColumn = struct {
        line: u32,
        column: u32,
    };

    pub const ArrayInit = struct {
        ty: Ref,
        init_count: u32,
    };

    pub const Src = struct {
        node: Ast.Node.Offset,
        line: u32,
        column: u32,
    };

    pub const ValidateDestructure = struct {
        /// The value being destructured.
        operand: Ref,
        /// The `destructure_assign` node.
        destructure_node: Ast.Node.Offset,
        /// The expected field count.
        expect_len: u32,
    };

    pub const RestoreErrRetIndex = struct {
        src_node: Ast.Node.Offset,
        /// If `.none`, restore the trace to its state upon function entry.
        block: Ref,
        /// If `.none`, restore unconditionally.
        operand: Ref,
    };

    pub const Import = struct {
        /// The result type of the import, or `.none` if none was available.
        res_ty: Ref,
        /// The import path.
        path: NullTerminatedString,
    };
};

/// `DeclContents` contains all "interesting" instructions found within a declaration by `findTrackable`.
/// These instructions are partitioned into a few different sets, since this makes ZIR instruction mapping
/// more effective.
pub const DeclContents = struct {
    /// This is a simple optional because ZIR guarantees that a `func`/`func_inferred`/`func_fancy` instruction
    /// can only occur once per `declaration`.
    func_decl: ?Inst.Index,
    type_decls: std.ArrayList(Inst.Index),
    other: std.ArrayList(Inst.Index),

    pub const init: DeclContents = .{
        .func_decl = null,
        .type_decls = .empty,
        .other = .empty,
    };

    pub fn clear(contents: *DeclContents) void {
        contents.func_decl = null;
        contents.type_decls.clearRetainingCapacity();
        contents.other.clearRetainingCapacity();
    }

    pub fn deinit(contents: *DeclContents, gpa: Allocator) void {
        contents.type_decls.deinit(gpa);
        contents.other.deinit(gpa);
    }
};

/// Find all tracked ZIR instructions, recursively, within a `declaration` instruction. Does not recurse through
/// nested declarations; to find all declarations, call this function recursively on the type declarations discovered
/// in `contents.type_decls`.
///
/// This populates an `ArrayList` because an iterator would need to allocate memory anyway.
pub fn findTrackable(zir: Zir, gpa: Allocator, contents: *DeclContents, decl_inst: Zir.Inst.Index) !void {
    contents.clear();

    const decl = zir.getDeclaration(decl_inst);

    // `defer` instructions duplicate the same body arbitrarily many times, but we only want to traverse
    // their contents once per defer. So, we store the extra index of the body here to deduplicate.
    var found_defers: std.AutoHashMapUnmanaged(u32, void) = .empty;
    defer found_defers.deinit(gpa);

    if (decl.type_body) |b| try zir.findTrackableBody(gpa, contents, &found_defers, b);
    if (decl.align_body) |b| try zir.findTrackableBody(gpa, contents, &found_defers, b);
    if (decl.linksection_body) |b| try zir.findTrackableBody(gpa, contents, &found_defers, b);
    if (decl.addrspace_body) |b| try zir.findTrackableBody(gpa, contents, &found_defers, b);
    if (decl.value_body) |b| try zir.findTrackableBody(gpa, contents, &found_defers, b);
}

/// `findTrackable` does not recurse into field expressions in a type. Instead, this function will
/// scan specifically field expressions in a given type declaration for trackable ZIR instructions.
pub fn findTrackableFields(
    zir: *const Zir,
    gpa: Allocator,
    contents: *DeclContents,
    type_decl_inst: Zir.Inst.Index,
) Allocator.Error!void {
    contents.clear();

    var found_defers: std.AutoHashMapUnmanaged(u32, void) = .empty;
    defer found_defers.deinit(gpa);

    assert(zir.instructions.items(.tag)[@backingInt(type_decl_inst)] == .extended);
    switch (zir.instructions.items(.data)[@backingInt(type_decl_inst)].extended.opcode) {
        .struct_decl => {
            const struct_decl = zir.getStructDecl(type_decl_inst);
            var it = struct_decl.iterateFields();
            while (it.next()) |field| {
                try zir.findTrackableBody(gpa, contents, &found_defers, field.type_body);
                if (field.align_body) |b| try zir.findTrackableBody(gpa, contents, &found_defers, b);
                if (field.default_body) |b| try zir.findTrackableBody(gpa, contents, &found_defers, b);
            }
        },
        .union_decl => {
            const union_decl = zir.getUnionDecl(type_decl_inst);
            var it = union_decl.iterateFields();
            while (it.next()) |field| {
                if (field.type_body) |b| try zir.findTrackableBody(gpa, contents, &found_defers, b);
                if (field.align_body) |b| try zir.findTrackableBody(gpa, contents, &found_defers, b);
                if (field.value_body) |b| try zir.findTrackableBody(gpa, contents, &found_defers, b);
            }
        },
        .enum_decl => {
            const enum_decl = zir.getEnumDecl(type_decl_inst);
            var it = enum_decl.iterateFields();
            while (it.next()) |field| {
                if (field.value_body) |b| try zir.findTrackableBody(gpa, contents, &found_defers, b);
            }
        },
        .opaque_decl => {},
        else => unreachable,
    }
}

fn findTrackableInner(
    zir: Zir,
    gpa: Allocator,
    contents: *DeclContents,
    defers: *std.AutoHashMapUnmanaged(u32, void),
    inst: Inst.Index,
) Allocator.Error!void {
    comptime assert(Zir.inst_tracking_version == 0);

    const tags = zir.instructions.items(.tag);
    const datas = zir.instructions.items(.data);

    switch (tags[@backingInt(inst)]) {
        .declaration => unreachable,

        // Boring instruction tags first. These have no body and are not declarations or type declarations.
        .add,
        .addwrap,
        .add_sat,
        .add_unsafe,
        .sub,
        .subwrap,
        .sub_sat,
        .mul,
        .mulwrap,
        .mul_sat,
        .div_exact,
        .div_floor,
        .div_ceil,
        .div_trunc,
        .mod,
        .rem,
        .mod_rem,
        .shl,
        .shl_exact,
        .shl_sat,
        .shr,
        .shr_exact,
        .param_anytype,
        .param_anytype_comptime,
        .array_cat,
        .array_type,
        .array_type_sentinel,
        .reify_int,
        .vector_type,
        .elem_type,
        .indexable_ptr_elem_type,
        .splat_op_result_ty,
        .from_backing_int_arg_ty,
        .indexable_ptr_len,
        .anyframe_type,
        .as_node,
        .as_shift_operand,
        .bit_and,
        .bitcast,
        .bit_not,
        .bit_or,
        .bool_not,
        .bool_br_and,
        .bool_br_or,
        .@"break",
        .break_inline,
        .switch_continue,
        .check_comptime_control_flow,
        .builtin_call,
        .cmp_lt,
        .cmp_lte,
        .cmp_eq,
        .cmp_gte,
        .cmp_gt,
        .cmp_neq,
        .error_set_decl,
        .dbg_stmt,
        .dbg_var_ptr,
        .dbg_var_val,
        .decl_ref,
        .decl_val,
        .load,
        .div,
        .elem_ptr_node,
        .elem_ptr,
        .elem_ptr_load,
        .elem_val,
        .elem_val_imm,
        .ensure_result_used,
        .ensure_result_non_error,
        .ensure_err_union_payload_void,
        .error_union_type,
        .error_value,
        .@"export",
        .field_ptr,
        .field_ptr_load,
        .field_ptr_named,
        .field_ptr_named_load,
        .import,
        .int,
        .int_big,
        .float,
        .float128,
        .int_type,
        .is_non_null,
        .is_non_null_ptr,
        .is_non_err,
        .is_non_err_ptr,
        .ret_is_non_err,
        .repeat,
        .repeat_inline,
        .for_len,
        .merge_error_sets,
        .ref,
        .deref,
        .ref_deref,
        .ret_node,
        .ret_load,
        .ret_implicit,
        .ret_err_value,
        .ret_ptr,
        .ret_type,
        .ptr_type,
        .slice_start,
        .slice_end,
        .slice_sentinel,
        .slice_length,
        .slice_sentinel_ty,
        .store_node,
        .store_to_inferred_ptr,
        .str,
        .negate,
        .negate_wrap,
        .typeof,
        .typeof_log2_int_type,
        .@"unreachable",
        .xor,
        .optional_type,
        .optional_payload_safe,
        .optional_payload_unsafe,
        .optional_payload_safe_ptr,
        .optional_payload_unsafe_ptr,
        .err_union_payload_unsafe,
        .err_union_payload_unsafe_ptr,
        .err_union_code,
        .err_union_code_ptr,
        .enum_literal,
        .decl_literal,
        .decl_literal_no_coerce,
        .validate_destructure,
        .field_type_ref,
        .opt_eu_base_ptr_init,
        .coerce_ptr_elem_ty,
        .validate_ref_ty,
        .validate_const,
        .struct_init_empty,
        .struct_init_empty_result,
        .struct_init_empty_ref_result,
        .validate_struct_init_ty,
        .validate_struct_init_result_ty,
        .validate_ptr_struct_init,
        .struct_init_field_type,
        .struct_init_field_ptr,
        .array_init_anon,
        .array_init,
        .array_init_ref,
        .validate_array_init_ty,
        .validate_array_init_result_ty,
        .validate_array_init_ref_ty,
        .validate_ptr_array_init,
        .array_init_elem_type,
        .array_init_elem_ptr,
        .union_init,
        .type_info,
        .size_of,
        .bit_size_of,
        .int_from_ptr,
        .compile_error,
        .set_eval_branch_quota,
        .int_from_enum,
        .align_of,
        .int_from_bool,
        .embed_file,
        .error_name,
        .panic,
        .trap,
        .set_runtime_safety,
        .sqrt,
        .sin,
        .cos,
        .tan,
        .exp,
        .exp2,
        .log,
        .log2,
        .log10,
        .abs,
        .floor,
        .ceil,
        .trunc,
        .round,
        .tag_name,
        .type_name,
        .frame_type,
        .int_from_float,
        .float_from_int,
        .ptr_from_int,
        .enum_from_int,
        .backing_int,
        .from_backing_int,
        .float_cast,
        .int_cast,
        .ptr_cast,
        .truncate,
        .has_decl,
        .has_field,
        .clz,
        .ctz,
        .pop_count,
        .byte_swap,
        .bit_reverse,
        .bit_offset_of,
        .offset_of,
        .splat,
        .reduce,
        .shuffle,
        .atomic_load,
        .atomic_rmw,
        .atomic_store,
        .mul_add,
        .memcpy,
        .memset,
        .memmove,
        .min,
        .max,
        .alloc,
        .alloc_mut,
        .alloc_comptime_mut,
        .alloc_inferred,
        .alloc_inferred_mut,
        .alloc_inferred_comptime,
        .alloc_inferred_comptime_mut,
        .resolve_inferred_alloc,
        .make_ptr_const,
        .@"resume",
        .save_err_ret_index,
        .restore_err_ret_index_unconditional,
        .restore_err_ret_index_fn_entry,
        => return,

        // Struct initializations need tracking, as they may create anonymous struct types.
        .struct_init,
        .struct_init_ref,
        .struct_init_anon,
        => return contents.other.append(gpa, inst),

        .extended => {
            const extended = datas[@backingInt(inst)].extended;
            switch (extended.opcode) {
                .value_placeholder => unreachable,

                // Once again, we start with the boring tags.
                .this,
                .ret_addr,
                .builtin_src,
                .error_return_trace,
                .frame,
                .frame_address,
                .alloc,
                .builtin_extern,
                .@"asm",
                .asm_expr,
                .compile_log,
                .min_multi,
                .max_multi,
                .add_with_overflow,
                .sub_with_overflow,
                .mul_with_overflow,
                .shl_with_overflow,
                .round_op,
                .wasm_memory_size,
                .wasm_memory_grow,
                .prefetch,
                .set_float_mode,
                .error_cast,
                .breakpoint,
                .disable_instrumentation,
                .disable_intrinsics,
                .select,
                .int_from_error,
                .error_from_int,
                .reify_slice_arg_ty,
                .reify_enum_value_slice_ty,
                .reify_pointer_sentinel_ty,
                .reify_tuple,
                .reify_pointer,
                .reify_fn,
                .cmpxchg,
                .c_va_arg,
                .c_va_copy,
                .c_va_end,
                .c_va_start,
                .ptr_cast_full,
                .ptr_cast_no_dest,
                .work_item_id,
                .work_group_size,
                .work_group_id,
                .in_comptime,
                .restore_err_ret_index,
                .closure_get,
                .field_parent_ptr,
                .std_lang_value,
                .branch_hint,
                .inplace_arith_result_ty,
                .tuple_decl,
                .dbg_empty_stmt,
                .astgen_error,
                .float_op_result_ty,
                .round_op_ty,
                => return,

                // `@TypeOf` has a body.
                .typeof_peer => {
                    const extra = zir.extraData(Zir.Inst.TypeOfPeer, extended.operand);
                    const body = zir.bodySlice(extra.data.body_index, extra.data.body_len);
                    try zir.findTrackableBody(gpa, contents, defers, body);
                },

                // Reifications need tracking.
                .reify_enum,
                .reify_struct,
                .reify_union,
                .reify_spirv_type,
                => return contents.other.append(gpa, inst),

                // Type declarations need tracking.
                .struct_decl,
                .union_decl,
                .enum_decl,
                .opaque_decl,
                => return contents.type_decls.append(gpa, inst),
            }
        },

        // Functions instructions are interesting and have a body.
        .func,
        .func_inferred,
        => {
            const inst_data = datas[@backingInt(inst)].pl_node;
            const extra = zir.extraData(Inst.Func, inst_data.payload_index);

            if (extra.data.body_len == 0) {
                // This is just a prototype. No need to track.
                assert(extra.data.ret_ty.body_len < 2);
                return;
            }

            assert(contents.func_decl == null);
            contents.func_decl = inst;

            var extra_index: usize = extra.end;
            switch (extra.data.ret_ty.body_len) {
                0 => {},
                1 => extra_index += 1,
                else => {
                    const body = zir.bodySlice(extra_index, extra.data.ret_ty.body_len);
                    extra_index += body.len;
                    try zir.findTrackableBody(gpa, contents, defers, body);
                },
            }
            const body = zir.bodySlice(extra_index, extra.data.body_len);
            return zir.findTrackableBody(gpa, contents, defers, body);
        },
        .func_fancy => {
            const inst_data = datas[@backingInt(inst)].pl_node;
            const extra = zir.extraData(Inst.FuncFancy, inst_data.payload_index);

            if (extra.data.body_len == 0) {
                // This is just a prototype. No need to track.
                assert(!extra.data.bits.has_cc_body);
                assert(!extra.data.bits.has_ret_ty_body);
                return;
            }

            assert(contents.func_decl == null);
            contents.func_decl = inst;

            var extra_index: usize = extra.end;

            if (extra.data.bits.has_cc_body) {
                const body_len = zir.extra[extra_index];
                extra_index += 1;
                const body = zir.bodySlice(extra_index, body_len);
                try zir.findTrackableBody(gpa, contents, defers, body);
                extra_index += body.len;
            } else if (extra.data.bits.has_cc_ref) {
                extra_index += 1;
            }

            if (extra.data.bits.has_ret_ty_body) {
                const body_len = zir.extra[extra_index];
                extra_index += 1;
                const body = zir.bodySlice(extra_index, body_len);
                try zir.findTrackableBody(gpa, contents, defers, body);
                extra_index += body.len;
            } else if (extra.data.bits.has_ret_ty_ref) {
                extra_index += 1;
            }

            extra_index += @intFromBool(extra.data.bits.has_any_noalias);

            const body = zir.bodySlice(extra_index, extra.data.body_len);
            return zir.findTrackableBody(gpa, contents, defers, body);
        },

        // Block instructions, recurse over the bodies.

        .block,
        .block_inline,
        .typeof_builtin,
        .loop,
        => {
            const inst_data = datas[@backingInt(inst)].pl_node;
            const extra = zir.extraData(Inst.Block, inst_data.payload_index);
            const body = zir.bodySlice(extra.end, extra.data.body_len);
            return zir.findTrackableBody(gpa, contents, defers, body);
        },
        .block_comptime => {
            const inst_data = datas[@backingInt(inst)].pl_node;
            const extra = zir.extraData(Inst.BlockComptime, inst_data.payload_index);
            const body = zir.bodySlice(extra.end, extra.data.body_len);
            return zir.findTrackableBody(gpa, contents, defers, body);
        },
        .condbr, .condbr_inline => {
            const inst_data = datas[@backingInt(inst)].pl_node;
            const extra = zir.extraData(Inst.CondBr, inst_data.payload_index);
            const then_body = zir.bodySlice(extra.end, extra.data.then_body_len);
            const else_body = zir.bodySlice(extra.end + then_body.len, extra.data.else_body_len);
            try zir.findTrackableBody(gpa, contents, defers, then_body);
            try zir.findTrackableBody(gpa, contents, defers, else_body);
        },
        .@"try", .try_ptr => {
            const inst_data = datas[@backingInt(inst)].pl_node;
            const extra = zir.extraData(Inst.Try, inst_data.payload_index);
            const body = zir.bodySlice(extra.end, extra.data.body_len);
            try zir.findTrackableBody(gpa, contents, defers, body);
        },

        .switch_block,
        .switch_block_ref,
        .switch_block_err_union,
        => {
            const zir_switch = zir.getSwitchBlock(inst);
            if (zir_switch.non_err_case) |non_err_case| {
                try zir.findTrackableBody(gpa, contents, defers, non_err_case.body);
            }
            if (zir_switch.else_case) |else_case| {
                try zir.findTrackableBody(gpa, contents, defers, else_case.body);
            }
            var extra_index = zir_switch.end;
            var case_it = zir_switch.iterateCases();
            while (case_it.next()) |case| {
                const prong_body = zir.bodySlice(extra_index, case.prong_info.body_len);
                extra_index += prong_body.len;
                try zir.findTrackableBody(gpa, contents, defers, prong_body);
                for (case.item_infos) |item_info| {
                    if (item_info.bodyLen()) |body_len| {
                        const item_body = zir.bodySlice(extra_index, body_len);
                        extra_index += item_body.len;
                        try zir.findTrackableBody(gpa, contents, defers, item_body);
                    }
                }
                for (case.range_infos) |range_info| {
                    if (range_info[0].bodyLen()) |body_len| {
                        const first_body = zir.bodySlice(extra_index, body_len);
                        extra_index += first_body.len;
                        try zir.findTrackableBody(gpa, contents, defers, first_body);
                    }
                    if (range_info[1].bodyLen()) |body_len| {
                        const last_body = zir.bodySlice(extra_index, body_len);
                        extra_index += last_body.len;
                        try zir.findTrackableBody(gpa, contents, defers, last_body);
                    }
                }
            }
        },

        .suspend_block => @panic("TODO iterate suspend block"),

        .param, .param_comptime => {
            const inst_data = datas[@backingInt(inst)].pl_tok;
            const extra = zir.extraData(Inst.Param, inst_data.payload_index);
            const body = zir.bodySlice(extra.end, extra.data.type.body_len);
            try zir.findTrackableBody(gpa, contents, defers, body);
        },

        inline .call, .field_call => |tag| {
            const inst_data = datas[@backingInt(inst)].pl_node;
            const extra = zir.extraData(switch (tag) {
                .call => Inst.Call,
                .field_call => Inst.FieldCall,
                else => unreachable,
            }, inst_data.payload_index);
            // It's easiest to just combine all the arg bodies into one body, like we do above for `struct_decl`.
            const args_len = extra.data.flags.args_len;
            if (args_len > 0) {
                const first_arg_start_off = args_len;
                const final_arg_end_off = zir.extra[extra.end + args_len - 1];
                const args_body = zir.bodySlice(extra.end + first_arg_start_off, final_arg_end_off - first_arg_start_off);
                try zir.findTrackableBody(gpa, contents, defers, args_body);
            }
        },
        .@"defer" => {
            const inst_data = datas[@backingInt(inst)].@"defer";
            const gop = try defers.getOrPut(gpa, inst_data.index);
            if (!gop.found_existing) {
                const body = zir.bodySlice(inst_data.index, inst_data.len);
                try zir.findTrackableBody(gpa, contents, defers, body);
            }
        },
    }
}

fn findTrackableBody(
    zir: Zir,
    gpa: Allocator,
    contents: *DeclContents,
    defers: *std.AutoHashMapUnmanaged(u32, void),
    body: []const Inst.Index,
) Allocator.Error!void {
    for (body) |member| {
        try zir.findTrackableInner(gpa, contents, defers, member);
    }
}

pub const FnInfo = struct {
    param_body: []const Inst.Index,
    param_body_inst: Inst.Index,
    ret_ty_body: []const Inst.Index,
    body: []const Inst.Index,
    ret_ty_ref: Zir.Inst.Ref,
    ret_ty_is_generic: bool,
    total_params_len: u32,
    inferred_error_set: bool,
};

pub fn getParamBody(zir: Zir, fn_inst: Inst.Index) []const Zir.Inst.Index {
    const tags = zir.instructions.items(.tag);
    const datas = zir.instructions.items(.data);
    const inst_data = datas[@backingInt(fn_inst)].pl_node;

    const param_block_index = switch (tags[@backingInt(fn_inst)]) {
        .func, .func_inferred => blk: {
            const extra = zir.extraData(Inst.Func, inst_data.payload_index);
            break :blk extra.data.param_block;
        },
        .func_fancy => blk: {
            const extra = zir.extraData(Inst.FuncFancy, inst_data.payload_index);
            break :blk extra.data.param_block;
        },
        else => unreachable,
    };

    switch (tags[@backingInt(param_block_index)]) {
        .block, .block_comptime, .block_inline => {
            const param_block = zir.extraData(Inst.Block, datas[@backingInt(param_block_index)].pl_node.payload_index);
            return zir.bodySlice(param_block.end, param_block.data.body_len);
        },
        .declaration => {
            return zir.getDeclaration(param_block_index).value_body.?;
        },
        else => unreachable,
    }
}

pub fn getParamName(zir: Zir, param_inst: Inst.Index) ?NullTerminatedString {
    const inst = zir.instructions.get(@backingInt(param_inst));
    return switch (inst.tag) {
        .param, .param_comptime => zir.extraData(Inst.Param, inst.data.pl_tok.payload_index).data.name,
        .param_anytype, .param_anytype_comptime => inst.data.str_tok.start,
        else => null,
    };
}

pub fn getFnInfo(zir: Zir, fn_inst: Inst.Index) FnInfo {
    const tags = zir.instructions.items(.tag);
    const datas = zir.instructions.items(.data);
    const info: struct {
        param_block: Inst.Index,
        body: []const Inst.Index,
        ret_ty_ref: Inst.Ref,
        ret_ty_body: []const Inst.Index,
        ret_ty_is_generic: bool,
        ies: bool,
    } = switch (tags[@backingInt(fn_inst)]) {
        .func, .func_inferred => |tag| blk: {
            const inst_data = datas[@backingInt(fn_inst)].pl_node;
            const extra = zir.extraData(Inst.Func, inst_data.payload_index);

            var extra_index: usize = extra.end;
            var ret_ty_ref: Inst.Ref = .none;
            var ret_ty_body: []const Inst.Index = &.{};

            switch (extra.data.ret_ty.body_len) {
                0 => {
                    ret_ty_ref = .void_type;
                },
                1 => {
                    ret_ty_ref = @fromBackingInt(@intCast(zir.extra[extra_index]));
                    extra_index += 1;
                },
                else => {
                    ret_ty_body = zir.bodySlice(extra_index, extra.data.ret_ty.body_len);
                    extra_index += ret_ty_body.len;
                },
            }

            const body = zir.bodySlice(extra_index, extra.data.body_len);
            extra_index += body.len;

            break :blk .{
                .param_block = extra.data.param_block,
                .ret_ty_ref = ret_ty_ref,
                .ret_ty_body = ret_ty_body,
                .body = body,
                .ret_ty_is_generic = extra.data.ret_ty.is_generic,
                .ies = tag == .func_inferred,
            };
        },
        .func_fancy => blk: {
            const inst_data = datas[@backingInt(fn_inst)].pl_node;
            const extra = zir.extraData(Inst.FuncFancy, inst_data.payload_index);

            var extra_index: usize = extra.end;
            var ret_ty_ref: Inst.Ref = .none;
            var ret_ty_body: []const Inst.Index = &.{};

            if (extra.data.bits.has_cc_body) {
                extra_index += zir.extra[extra_index] + 1;
            } else if (extra.data.bits.has_cc_ref) {
                extra_index += 1;
            }
            if (extra.data.bits.has_ret_ty_body) {
                const body_len = zir.extra[extra_index];
                extra_index += 1;
                ret_ty_body = zir.bodySlice(extra_index, body_len);
                extra_index += ret_ty_body.len;
            } else if (extra.data.bits.has_ret_ty_ref) {
                ret_ty_ref = @fromBackingInt(@intCast(zir.extra[extra_index]));
                extra_index += 1;
            } else {
                ret_ty_ref = .void_type;
            }

            extra_index += @intFromBool(extra.data.bits.has_any_noalias);

            const body = zir.bodySlice(extra_index, extra.data.body_len);
            extra_index += body.len;
            break :blk .{
                .param_block = extra.data.param_block,
                .ret_ty_ref = ret_ty_ref,
                .ret_ty_body = ret_ty_body,
                .body = body,
                .ret_ty_is_generic = extra.data.bits.ret_ty_is_generic,
                .ies = extra.data.bits.is_inferred_error,
            };
        },
        else => unreachable,
    };
    const param_body = zir.getParamBody(fn_inst);
    var total_params_len: u32 = 0;
    for (param_body) |inst| {
        switch (tags[@backingInt(inst)]) {
            .param, .param_comptime, .param_anytype, .param_anytype_comptime => {
                total_params_len += 1;
            },
            else => continue,
        }
    }
    return .{
        .param_body = param_body,
        .param_body_inst = info.param_block,
        .ret_ty_body = info.ret_ty_body,
        .ret_ty_ref = info.ret_ty_ref,
        .body = info.body,
        .total_params_len = total_params_len,
        .ret_ty_is_generic = info.ret_ty_is_generic,
        .inferred_error_set = info.ies,
    };
}

pub fn getDeclaration(zir: Zir, inst: Zir.Inst.Index) Inst.Declaration.Unwrapped {
    assert(zir.instructions.items(.tag)[@backingInt(inst)] == .declaration);
    const pl_node = zir.instructions.items(.data)[@backingInt(inst)].declaration;
    const extra = zir.extraData(Inst.Declaration, pl_node.payload_index);

    const flags_vals: [2]u32 = .{ extra.data.flags_0, extra.data.flags_1 };
    const flags: Inst.Declaration.Flags = @bitCast(flags_vals);

    var extra_index = extra.end;

    const name: NullTerminatedString = if (flags.id.hasName()) name: {
        const name = zir.extra[extra_index];
        extra_index += 1;
        break :name @fromBackingInt(@intCast(name));
    } else .empty;

    const lib_name: NullTerminatedString = if (flags.id.hasLibName()) lib_name: {
        const lib_name = zir.extra[extra_index];
        extra_index += 1;
        break :lib_name @fromBackingInt(@intCast(lib_name));
    } else .empty;

    const type_body_len: u32 = if (flags.id.hasTypeBody()) len: {
        const len = zir.extra[extra_index];
        extra_index += 1;
        break :len len;
    } else 0;
    const align_body_len: u32, const linksection_body_len: u32, const addrspace_body_len: u32 = lens: {
        if (!flags.id.hasSpecialBodies()) break :lens .{ 0, 0, 0 };
        const lens = zir.extra[extra_index..][0..3].*;
        extra_index += 3;
        break :lens lens;
    };
    const value_body_len: u32 = if (flags.id.hasValueBody()) len: {
        const len = zir.extra[extra_index];
        extra_index += 1;
        break :len len;
    } else 0;

    const type_body = zir.bodySlice(extra_index, type_body_len);
    extra_index += type_body_len;
    const align_body = zir.bodySlice(extra_index, align_body_len);
    extra_index += align_body_len;
    const linksection_body = zir.bodySlice(extra_index, linksection_body_len);
    extra_index += linksection_body_len;
    const addrspace_body = zir.bodySlice(extra_index, addrspace_body_len);
    extra_index += addrspace_body_len;
    const value_body = zir.bodySlice(extra_index, value_body_len);
    extra_index += value_body_len;

    return .{
        .src_node = pl_node.src_node,

        .src_line = flags.src_line,
        .src_column = flags.src_column,

        .kind = flags.id.kind(),
        .name = name,
        .is_pub = flags.id.isPub(),
        .is_threadlocal = flags.id.isThreadlocal(),
        .linkage = flags.id.linkage(),
        .lib_name = lib_name,

        .type_body = if (type_body_len == 0) null else type_body,
        .align_body = if (align_body_len == 0) null else align_body,
        .linksection_body = if (linksection_body_len == 0) null else linksection_body,
        .addrspace_body = if (addrspace_body_len == 0) null else addrspace_body,
        .value_body = if (value_body_len == 0) null else value_body,
    };
}

pub fn getAssociatedSrcHash(zir: Zir, inst: Zir.Inst.Index) ?std.zig.SrcHash {
    const tag = zir.instructions.items(.tag);
    const data = zir.instructions.items(.data);
    switch (tag[@backingInt(inst)]) {
        .declaration => {
            const declaration = data[@backingInt(inst)].declaration;
            const extra = zir.extraData(Inst.Declaration, declaration.payload_index);
            return @bitCast([4]u32{
                extra.data.src_hash_0,
                extra.data.src_hash_1,
                extra.data.src_hash_2,
                extra.data.src_hash_3,
            });
        },
        .func, .func_inferred => {
            const pl_node = data[@backingInt(inst)].pl_node;
            const extra = zir.extraData(Inst.Func, pl_node.payload_index);
            if (extra.data.body_len == 0) {
                // Function type or extern fn - no associated hash
                return null;
            }
            const extra_index = extra.end +
                extra.data.ret_ty.body_len +
                extra.data.body_len +
                @typeInfo(Inst.Func.SrcLocs).@"struct".field_names.len;
            return @bitCast([4]u32{
                zir.extra[extra_index + 0],
                zir.extra[extra_index + 1],
                zir.extra[extra_index + 2],
                zir.extra[extra_index + 3],
            });
        },
        .func_fancy => {
            const pl_node = data[@backingInt(inst)].pl_node;
            const extra = zir.extraData(Inst.FuncFancy, pl_node.payload_index);
            if (extra.data.body_len == 0) {
                // Function type or extern fn - no associated hash
                return null;
            }
            const bits = extra.data.bits;
            var extra_index = extra.end;
            if (bits.has_cc_body) {
                const body_len = zir.extra[extra_index];
                extra_index += 1 + body_len;
            } else extra_index += @intFromBool(bits.has_cc_ref);
            if (bits.has_ret_ty_body) {
                const body_len = zir.extra[extra_index];
                extra_index += 1 + body_len;
            } else extra_index += @intFromBool(bits.has_ret_ty_ref);
            extra_index += @intFromBool(bits.has_any_noalias);
            extra_index += extra.data.body_len;
            extra_index += @typeInfo(Zir.Inst.Func.SrcLocs).@"struct".field_names.len;
            return @bitCast([4]u32{
                zir.extra[extra_index + 0],
                zir.extra[extra_index + 1],
                zir.extra[extra_index + 2],
                zir.extra[extra_index + 3],
            });
        },
        .extended => {},
        else => return null,
    }
    const extended = data[@backingInt(inst)].extended;
    switch (extended.opcode) {
        .struct_decl => {
            const extra = zir.extraData(Inst.StructDecl, extended.operand).data;
            return @bitCast([4]u32{
                extra.fields_hash_0,
                extra.fields_hash_1,
                extra.fields_hash_2,
                extra.fields_hash_3,
            });
        },
        .union_decl => {
            const extra = zir.extraData(Inst.UnionDecl, extended.operand).data;
            return @bitCast([4]u32{
                extra.fields_hash_0,
                extra.fields_hash_1,
                extra.fields_hash_2,
                extra.fields_hash_3,
            });
        },
        .enum_decl => {
            const extra = zir.extraData(Inst.EnumDecl, extended.operand).data;
            return @bitCast([4]u32{
                extra.fields_hash_0,
                extra.fields_hash_1,
                extra.fields_hash_2,
                extra.fields_hash_3,
            });
        },
        else => return null,
    }
}

pub fn getSwitchBlock(zir: *const Zir, switch_inst: Inst.Index) UnwrappedSwitchBlock {
    const has_non_err = switch (zir.instructions.items(.tag)[@backingInt(switch_inst)]) {
        .switch_block, .switch_block_ref => false,
        .switch_block_err_union => true,
        else => unreachable,
    };
    const inst_data = zir.instructions.items(.data)[@backingInt(switch_inst)].pl_node;
    const extra = zir.extraData(Inst.SwitchBlock, inst_data.payload_index);
    const bits = extra.data.bits;
    var extra_index = extra.end;
    const multi_cases_len = if (bits.has_multi_cases) len: {
        const multi_cases_len = zir.extra[extra_index];
        extra_index += 1;
        break :len multi_cases_len;
    } else 0;
    const payload_capture_placeholder: Inst.OptionalIndex = if (bits.payload_capture_inst_is_placeholder) inst: {
        const inst: Inst.Index = @fromBackingInt(@intCast(zir.extra[extra_index]));
        extra_index += 1;
        break :inst inst.toOptional();
    } else .none;
    const tag_capture_placeholder: Inst.OptionalIndex = if (bits.tag_capture_inst_is_placeholder) inst: {
        const inst: Inst.Index = @fromBackingInt(@intCast(zir.extra[extra_index]));
        extra_index += 1;
        break :inst inst.toOptional();
    } else .none;
    const catch_or_if_src_node_offset: Ast.Node.OptionalOffset = if (has_non_err) node_offset: {
        const node_offset: Ast.Node.Offset = @fromBackingInt(@intCast(@as(i32, @bitCast(zir.extra[extra_index]))));
        extra_index += 1;
        break :node_offset node_offset.toOptional();
    } else .none;
    const non_err_info: Inst.SwitchBlock.ProngInfo.NonErr = if (has_non_err) non_err_info: {
        const non_err_info: Inst.SwitchBlock.ProngInfo.NonErr = @bitCast(zir.extra[extra_index]);
        extra_index += 1;
        break :non_err_info non_err_info;
    } else undefined;
    const else_info: Inst.SwitchBlock.ProngInfo.Else = if (bits.has_else) else_info: {
        const else_info: Inst.SwitchBlock.ProngInfo.Else = @bitCast(zir.extra[extra_index]);
        extra_index += 1;
        break :else_info else_info;
    } else undefined;
    const scalar_cases_len: u32 = bits.scalar_cases_len;
    const prong_infos: []const Inst.SwitchBlock.ProngInfo =
        @ptrCast(zir.extra[extra_index..][0 .. scalar_cases_len + multi_cases_len]);
    extra_index += prong_infos.len;
    const multi_case_items_lens = zir.extra[extra_index..][0..multi_cases_len];
    extra_index += multi_case_items_lens.len;
    const multi_case_ranges_lens: ?[]const u32 = if (bits.any_ranges) lens: {
        const multi_case_ranges_lens = zir.extra[extra_index..][0..multi_cases_len];
        extra_index += multi_case_ranges_lens.len;
        break :lens multi_case_ranges_lens;
    } else null;
    var total_items_len: usize = scalar_cases_len;
    for (multi_case_items_lens) |items_len| {
        total_items_len += items_len;
    }
    if (multi_case_ranges_lens) |ranges_lens| for (ranges_lens) |ranges_len| {
        total_items_len += 2 * ranges_len;
    };
    const item_infos: []const Inst.SwitchBlock.ItemInfo =
        @ptrCast(zir.extra[extra_index..][0..total_items_len]);
    extra_index += item_infos.len;
    const non_err_case: ?UnwrappedSwitchBlock.Case.NonErr = if (has_non_err) non_err_case: {
        const body = zir.bodySlice(extra_index, non_err_info.body_len);
        extra_index += body.len;
        break :non_err_case .{
            .body = body,
            .capture = non_err_info.capture,
            .operand_is_ref = non_err_info.operand_is_ref,
        };
    } else null;
    const else_case: ?UnwrappedSwitchBlock.Case.Else = if (bits.has_else) else_case: {
        const body = zir.bodySlice(extra_index, else_info.body_len);
        extra_index += body.len;
        break :else_case .{
            .index = .@"else",
            .body = body,
            .capture = else_info.capture,
            .is_inline = else_info.is_inline,
            .has_tag_capture = else_info.has_tag_capture,
            .is_simple_noreturn = else_info.is_simple_noreturn,
        };
    } else null;
    return .{
        .main_operand = extra.data.raw_operand,
        .switch_src_node_offset = inst_data.src_node,
        .catch_or_if_src_node_offset = catch_or_if_src_node_offset,
        .payload_capture_placeholder = payload_capture_placeholder,
        .tag_capture_placeholder = tag_capture_placeholder,
        .has_continue = bits.has_continue,
        .any_maybe_runtime_capture = bits.any_maybe_runtime_capture,
        .non_err_case = non_err_case,
        .else_case = else_case,
        .has_under = bits.has_under,
        .prong_infos = prong_infos,
        .multi_case_items_lens = multi_case_items_lens,
        .multi_case_ranges_lens = multi_case_ranges_lens,
        .item_infos = item_infos,
        .end = extra_index,
    };
}

/// Trailing (starting at `end`):
/// 0. case_bodies: { // for each case in Case.Iterator.next()
///        prong_body: {
///            body_inst: Inst.Index, // for every case.prong_info.body_len,
///        }
///        item_body: { // for each body_len in case.item_infos
///            body_inst: Inst.Index, // for every body_len
///        }
///        range_bodies: { // for each .{first_info, last_info} in case.range_infos
///            first_body_inst: Inst.Index, // for every first_info.body_len
///            last_body_inst: Inst.Index, // for every last_info.body_len
///        }
///    }
pub const UnwrappedSwitchBlock = struct {
    /// Either `catch`/`if` or `switch` operand.
    main_operand: Inst.Ref,
    switch_src_node_offset: Ast.Node.Offset,
    catch_or_if_src_node_offset: Ast.Node.OptionalOffset,
    payload_capture_placeholder: Inst.OptionalIndex,
    tag_capture_placeholder: Inst.OptionalIndex,
    has_continue: bool,
    any_maybe_runtime_capture: bool,
    non_err_case: ?Case.NonErr,
    else_case: ?Case.Else,
    has_under: bool,
    // Refer to doc comment and `iterateCases` to access everything below correctly.
    prong_infos: []const Inst.SwitchBlock.ProngInfo,
    multi_case_items_lens: []const u32,
    multi_case_ranges_lens: ?[]const u32,
    item_infos: []const Inst.SwitchBlock.ItemInfo,
    end: usize,

    pub fn anyRanges(unwrapped: *const UnwrappedSwitchBlock) bool {
        return unwrapped.multi_case_ranges_lens != null;
    }

    pub fn scalarCasesLen(unwrapped: *const UnwrappedSwitchBlock) u32 {
        return @intCast(unwrapped.prong_infos.len - unwrapped.multi_case_items_lens.len);
    }

    pub fn multiCasesLen(unwrapped: *const UnwrappedSwitchBlock) u32 {
        return @intCast(unwrapped.multi_case_items_lens.len);
    }

    pub fn totalItemsLen(unwrapped: *const UnwrappedSwitchBlock) u32 {
        var total_items_len: u32 = @intCast(unwrapped.item_infos.len);
        if (unwrapped.multi_case_ranges_lens) |ranges_lens| {
            for (ranges_lens) |len| total_items_len -= len;
        }
        return total_items_len;
    }

    pub const Case = struct {
        index: Case.Index,
        prong_info: Inst.SwitchBlock.ProngInfo,
        item_infos: []const Inst.SwitchBlock.ItemInfo,
        range_infos: []const [2]Inst.SwitchBlock.ItemInfo,

        pub const Index = packed struct(u32) {
            kind: enum(u1) { scalar, multi },
            value: u31,

            pub const @"else": Case.Index = .{
                .kind = .scalar,
                .value = std.math.maxInt(u31),
            };
        };

        pub const NonErr = struct {
            body: []const Inst.Index,
            capture: Inst.SwitchBlock.ProngInfo.Capture,
            operand_is_ref: bool,
        };

        pub const Else = struct {
            index: Case.Index,
            body: []const Inst.Index,
            capture: Inst.SwitchBlock.ProngInfo.Capture,
            is_inline: bool,
            has_tag_capture: bool,
            is_simple_noreturn: bool,
        };

        pub const Iterator = struct {
            next_idx: u32,
            prong_infos: []const Inst.SwitchBlock.ProngInfo,
            multi_case_items_lens: []const u32,
            multi_case_ranges_lens: ?[]const u32,
            item_infos: []const Inst.SwitchBlock.ItemInfo,

            pub fn next(it: *Iterator) ?Case {
                const idx = it.next_idx;
                if (idx == it.prong_infos.len) return null;
                it.next_idx += 1;
                const scalar_cases_len = it.prong_infos.len - it.multi_case_items_lens.len;
                return if (idx < scalar_cases_len) .{
                    .index = .{
                        .kind = .scalar,
                        .value = @intCast(idx),
                    },
                    .prong_info = it.prong_infos[idx],
                    .item_infos = it.itemInfos(1),
                    .range_infos = &.{},
                } else .{
                    .index = .{
                        .kind = .multi,
                        .value = @intCast(idx - scalar_cases_len),
                    },
                    .prong_info = it.prong_infos[idx],
                    .item_infos = it.itemInfos(it.multi_case_items_lens[idx - scalar_cases_len]),
                    .range_infos = if (it.multi_case_ranges_lens) |ranges_lens| b: {
                        break :b @ptrCast(it.itemInfos(2 * ranges_lens[idx - scalar_cases_len]));
                    } else &.{},
                };
            }
            fn itemInfos(it: *Iterator, count: u32) []const Inst.SwitchBlock.ItemInfo {
                const lens = it.item_infos[0..count];
                it.item_infos = it.item_infos[count..];
                return lens;
            }
        };
    };

    pub fn iterateCases(unwrapped: UnwrappedSwitchBlock) Case.Iterator {
        return .{
            .next_idx = 0,
            .prong_infos = unwrapped.prong_infos,
            .multi_case_items_lens = unwrapped.multi_case_items_lens,
            .multi_case_ranges_lens = unwrapped.multi_case_ranges_lens,
            .item_infos = unwrapped.item_infos,
        };
    }
};

/// When the ZIR update tracking logic must be modified to consider new instructions,
/// change this constant to trigger compile errors at all relevant locations.
pub const inst_tracking_version = 0;

/// Asserts that a ZIR instruction is tracked across incremental updates, and
/// thus may be given an `InternPool.TrackedInst`.
pub fn assertTrackable(zir: Zir, inst_idx: Zir.Inst.Index) void {
    comptime assert(Zir.inst_tracking_version == 0);
    const inst = zir.instructions.get(@backingInt(inst_idx));
    switch (inst.tag) {
        .struct_init,
        .struct_init_ref,
        .struct_init_anon,
        => {}, // tracked in order, as the owner instructions of anonymous struct types
        .func, .func_inferred => {
            // These are tracked provided they are actual function declarations, not just bodies.
            const extra = zir.extraData(Inst.Func, inst.data.pl_node.payload_index);
            assert(extra.data.body_len != 0);
        },
        .func_fancy => {
            // These are tracked provided they are actual function declarations, not just bodies.
            const extra = zir.extraData(Inst.FuncFancy, inst.data.pl_node.payload_index);
            assert(extra.data.body_len != 0);
        },
        .declaration => {}, // tracked by correlating names in the namespace of the parent container
        .extended => switch (inst.data.extended.opcode) {
            .struct_decl,
            .union_decl,
            .enum_decl,
            .opaque_decl,
            .reify_enum,
            .reify_struct,
            .reify_union,
            .reify_spirv_type,
            => {}, // tracked in order, as the owner instructions of explicit container types
            else => unreachable, // assertion failure; not trackable
        },
        else => unreachable, // assertion failure; not trackable
    }
}

pub fn typeDecls(zir: Zir, type_decl: Inst.Index) []const Zir.Inst.Index {
    const inst = zir.instructions.get(@backingInt(type_decl));
    assert(inst.tag == .extended);
    return switch (inst.data.extended.opcode) {
        .struct_decl => zir.getStructDecl(type_decl).decls,
        .union_decl => zir.getUnionDecl(type_decl).decls,
        .enum_decl => zir.getEnumDecl(type_decl).decls,
        .opaque_decl => zir.getOpaqueDecl(type_decl).decls,
        else => unreachable,
    };
}

pub fn getStructDecl(zir: *const Zir, struct_decl: Inst.Index) UnwrappedStructDecl {
    const inst_data = zir.instructions.get(@backingInt(struct_decl));
    assert(inst_data.tag == .extended);
    assert(inst_data.data.extended.opcode == .struct_decl);
    const small: Inst.StructDecl.Small = @bitCast(inst_data.data.extended.small);
    const extra = zir.extraData(Inst.StructDecl, inst_data.data.extended.operand);
    var extra_index = extra.end;
    const captures_len: u32 = if (small.has_captures_len) blk: {
        const captures_len = zir.extra[extra_index];
        extra_index += 1;
        break :blk captures_len;
    } else 0;
    const decls_len: u32 = if (small.has_decls_len) blk: {
        const decls_len = zir.extra[extra_index];
        extra_index += 1;
        break :blk decls_len;
    } else 0;
    const fields_len: u32 = if (small.has_fields_len) blk: {
        const fields_len = zir.extra[extra_index];
        extra_index += 1;
        break :blk fields_len;
    } else 0;
    const backing_int_type_body_len: u32 = if (small.has_backing_int_type) len: {
        const body_len = zir.extra[extra_index];
        extra_index += 1;
        break :len body_len;
    } else 0;
    const captures: []const Inst.Capture = @ptrCast(zir.extra[extra_index..][0..captures_len]);
    extra_index += captures_len;
    const capture_names: []const NullTerminatedString = @ptrCast(zir.extra[extra_index..][0..captures_len]);
    extra_index += captures_len;
    const decls: []const Inst.Index = @ptrCast(zir.extra[extra_index..][0..decls_len]);
    extra_index += decls_len;
    const field_names: []const NullTerminatedString = @ptrCast(zir.extra[extra_index..][0..fields_len]);
    extra_index += fields_len;
    const field_type_body_lens: []const u32 = @ptrCast(zir.extra[extra_index..][0..fields_len]);
    extra_index += fields_len;
    const field_align_body_lens: ?[]const u32 = if (small.any_field_aligns) lens: {
        const lens = zir.extra[extra_index..][0..fields_len];
        extra_index += fields_len;
        break :lens @ptrCast(lens);
    } else null;
    const field_default_body_lens: ?[]const u32 = if (small.any_field_defaults) lens: {
        const lens = zir.extra[extra_index..][0..fields_len];
        extra_index += fields_len;
        break :lens @ptrCast(lens);
    } else null;
    const field_comptime_bits: ?[]const u32 = if (small.any_comptime_fields) bits: {
        const bits_len = @divCeil(fields_len, 32);
        const bits = zir.extra[extra_index..][0..bits_len];
        extra_index += bits_len;
        break :bits bits;
    } else null;
    const backing_int_type_body: ?[]const Zir.Inst.Index = switch (backing_int_type_body_len) {
        0 => null,
        else => |n| zir.bodySlice(extra_index, n),
    };
    extra_index += backing_int_type_body_len;
    const field_bodies_overlong: []const Inst.Index = @ptrCast(zir.extra[extra_index..]);
    return .{
        .src_line = extra.data.src_line,
        .src_node = extra.data.src_node,
        .name_strategy = small.name_strategy,
        .captures = captures,
        .capture_names = capture_names,
        .decls = decls,
        .layout = small.layout,
        .backing_int_type_body = backing_int_type_body,
        .field_names = field_names,
        .field_type_body_lens = field_type_body_lens,
        .field_align_body_lens = field_align_body_lens,
        .field_default_body_lens = field_default_body_lens,
        .field_comptime_bits = field_comptime_bits,
        .field_bodies_overlong = field_bodies_overlong,
    };
}
pub const UnwrappedStructDecl = struct {
    src_line: u32,
    src_node: Ast.Node.Index,
    name_strategy: Inst.NameStrategy,

    captures: []const Inst.Capture,
    capture_names: []const NullTerminatedString,

    decls: []const Inst.Index,

    layout: std.lang.Type.ContainerLayout,
    backing_int_type_body: ?[]const Inst.Index,

    field_names: []const NullTerminatedString,
    field_type_body_lens: []const u32,
    field_align_body_lens: ?[]const u32,
    field_default_body_lens: ?[]const u32,
    field_comptime_bits: ?[]const u32,
    field_bodies_overlong: []const Inst.Index,

    pub fn iterateFields(struct_decl: UnwrappedStructDecl) FieldIterator {
        return .{
            .next_idx = 0,
            .names = struct_decl.field_names,
            .type_body_lens = struct_decl.field_type_body_lens,
            .align_body_lens = struct_decl.field_align_body_lens,
            .default_body_lens = struct_decl.field_default_body_lens,
            .comptime_bits = struct_decl.field_comptime_bits,
            .bodies_overlong = struct_decl.field_bodies_overlong,
        };
    }

    pub const FieldIterator = struct {
        next_idx: u32,
        names: []const NullTerminatedString,
        type_body_lens: []const u32,
        align_body_lens: ?[]const u32,
        default_body_lens: ?[]const u32,
        comptime_bits: ?[]const u32,
        bodies_overlong: []const Inst.Index,
        pub const Field = struct {
            idx: u32,
            name: NullTerminatedString,
            type_body: []const Inst.Index,
            align_body: ?[]const Inst.Index,
            default_body: ?[]const Inst.Index,
            is_comptime: bool,
        };
        pub fn next(it: *FieldIterator) ?Field {
            const idx = it.next_idx;
            if (idx == it.names.len) return null;
            it.next_idx += 1;
            return .{
                .idx = idx,
                .name = it.names[idx],
                .type_body = it.body(it.type_body_lens[idx]).?,
                .align_body = it.body(if (it.align_body_lens) |l| l[idx] else 0),
                .default_body = it.body(if (it.default_body_lens) |l| l[idx] else 0),
                .is_comptime = ct: {
                    const bits = it.comptime_bits orelse break :ct false;
                    const big = bits[idx / 32];
                    const shifted = big >> @intCast(idx % 32);
                    break :ct @as(u1, @truncate(shifted)) == 1;
                },
            };
        }
        fn body(it: *FieldIterator, len: u32) ?[]const Inst.Index {
            if (len == 0) return null;
            const b = it.bodies_overlong[0..len];
            it.bodies_overlong = it.bodies_overlong[len..];
            return b;
        }
    };
};

pub fn getUnionDecl(zir: *const Zir, union_decl: Inst.Index) UnwrappedUnionDecl {
    const inst_data = zir.instructions.get(@backingInt(union_decl));
    assert(inst_data.tag == .extended);
    assert(inst_data.data.extended.opcode == .union_decl);
    const small: Inst.UnionDecl.Small = @bitCast(inst_data.data.extended.small);
    const extra = zir.extraData(Inst.UnionDecl, inst_data.data.extended.operand);
    var extra_index = extra.end;
    const captures_len: u32 = if (small.has_captures_len) blk: {
        const captures_len = zir.extra[extra_index];
        extra_index += 1;
        break :blk captures_len;
    } else 0;
    const decls_len: u32 = if (small.has_decls_len) blk: {
        const decls_len = zir.extra[extra_index];
        extra_index += 1;
        break :blk decls_len;
    } else 0;
    const fields_len: u32 = if (small.has_fields_len) blk: {
        const fields_len = zir.extra[extra_index];
        extra_index += 1;
        break :blk fields_len;
    } else 0;
    const arg_type_body_len: u32 = if (small.kind.hasArgType()) len: {
        const body_len = zir.extra[extra_index];
        extra_index += 1;
        break :len body_len;
    } else 0;
    const captures: []const Inst.Capture = @ptrCast(zir.extra[extra_index..][0..captures_len]);
    extra_index += captures_len;
    const capture_names: []const NullTerminatedString = @ptrCast(zir.extra[extra_index..][0..captures_len]);
    extra_index += captures_len;
    const decls: []const Inst.Index = @ptrCast(zir.extra[extra_index..][0..decls_len]);
    extra_index += decls_len;
    const field_names: []const NullTerminatedString = @ptrCast(zir.extra[extra_index..][0..fields_len]);
    extra_index += fields_len;
    const field_type_body_lens: []const u32 = @ptrCast(zir.extra[extra_index..][0..fields_len]);
    extra_index += fields_len;
    const field_align_body_lens: ?[]const u32 = if (small.any_field_aligns) lens: {
        const lens = zir.extra[extra_index..][0..fields_len];
        extra_index += fields_len;
        break :lens @ptrCast(lens);
    } else null;
    const field_value_body_lens: ?[]const u32 = if (small.any_field_values) lens: {
        const lens = zir.extra[extra_index..][0..fields_len];
        extra_index += fields_len;
        break :lens @ptrCast(lens);
    } else null;
    const arg_type_body: ?[]const Zir.Inst.Index = switch (arg_type_body_len) {
        0 => null,
        else => |n| zir.bodySlice(extra_index, n),
    };
    extra_index += arg_type_body_len;
    const field_bodies_overlong: []const Inst.Index = @ptrCast(zir.extra[extra_index..]);
    return .{
        .src_line = extra.data.src_line,
        .src_node = extra.data.src_node,
        .name_strategy = small.name_strategy,
        .captures = captures,
        .capture_names = capture_names,
        .decls = decls,
        .kind = small.kind,
        .arg_type_body = arg_type_body,
        .field_names = field_names,
        .field_type_body_lens = field_type_body_lens,
        .field_align_body_lens = field_align_body_lens,
        .field_value_body_lens = field_value_body_lens,
        .field_bodies_overlong = field_bodies_overlong,
    };
}
pub const UnwrappedUnionDecl = struct {
    src_line: u32,
    src_node: Ast.Node.Index,
    name_strategy: Inst.NameStrategy,

    captures: []const Inst.Capture,
    capture_names: []const NullTerminatedString,

    decls: []const Inst.Index,

    kind: Inst.UnionDecl.Kind,
    arg_type_body: ?[]const Inst.Index,

    field_names: []const NullTerminatedString,
    field_type_body_lens: []const u32,
    field_align_body_lens: ?[]const u32,
    field_value_body_lens: ?[]const u32,
    field_bodies_overlong: []const Inst.Index,

    pub fn iterateFields(union_decl: UnwrappedUnionDecl) FieldIterator {
        return .{
            .next_idx = 0,
            .names = union_decl.field_names,
            .type_body_lens = union_decl.field_type_body_lens,
            .align_body_lens = union_decl.field_align_body_lens,
            .value_body_lens = union_decl.field_value_body_lens,
            .bodies_overlong = union_decl.field_bodies_overlong,
        };
    }

    pub const FieldIterator = struct {
        next_idx: u32,
        names: []const NullTerminatedString,
        type_body_lens: []const u32,
        align_body_lens: ?[]const u32,
        value_body_lens: ?[]const u32,
        bodies_overlong: []const Inst.Index,
        pub const Field = struct {
            idx: u32,
            name: NullTerminatedString,
            type_body: ?[]const Inst.Index,
            align_body: ?[]const Inst.Index,
            value_body: ?[]const Inst.Index,
        };
        pub fn next(it: *FieldIterator) ?Field {
            const idx = it.next_idx;
            if (idx == it.names.len) return null;
            it.next_idx += 1;
            return .{
                .idx = idx,
                .name = it.names[idx],
                .type_body = it.body(it.type_body_lens[idx]),
                .align_body = it.body(if (it.align_body_lens) |l| l[idx] else 0),
                .value_body = it.body(if (it.value_body_lens) |l| l[idx] else 0),
            };
        }
        fn body(it: *FieldIterator, len: u32) ?[]const Inst.Index {
            if (len == 0) return null;
            const b = it.bodies_overlong[0..len];
            it.bodies_overlong = it.bodies_overlong[len..];
            return b;
        }
    };
};

pub fn getEnumDecl(zir: *const Zir, enum_decl: Inst.Index) UnwrappedEnumDecl {
    const inst_data = zir.instructions.get(@backingInt(enum_decl));
    assert(inst_data.tag == .extended);
    assert(inst_data.data.extended.opcode == .enum_decl);
    const small: Inst.EnumDecl.Small = @bitCast(inst_data.data.extended.small);
    const extra = zir.extraData(Inst.EnumDecl, inst_data.data.extended.operand);
    var extra_index = extra.end;
    const captures_len: u32 = if (small.has_captures_len) blk: {
        const captures_len = zir.extra[extra_index];
        extra_index += 1;
        break :blk captures_len;
    } else 0;
    const decls_len: u32 = if (small.has_decls_len) blk: {
        const decls_len = zir.extra[extra_index];
        extra_index += 1;
        break :blk decls_len;
    } else 0;
    const fields_len: u32 = if (small.has_fields_len) blk: {
        const fields_len = zir.extra[extra_index];
        extra_index += 1;
        break :blk fields_len;
    } else 0;
    const tag_type_body_len: u32 = if (small.has_tag_type) len: {
        const body_len = zir.extra[extra_index];
        extra_index += 1;
        break :len body_len;
    } else 0;
    const captures: []const Inst.Capture = @ptrCast(zir.extra[extra_index..][0..captures_len]);
    extra_index += captures_len;
    const capture_names: []const NullTerminatedString = @ptrCast(zir.extra[extra_index..][0..captures_len]);
    extra_index += captures_len;
    const decls: []const Inst.Index = @ptrCast(zir.extra[extra_index..][0..decls_len]);
    extra_index += decls_len;
    const field_names: []const NullTerminatedString = @ptrCast(zir.extra[extra_index..][0..fields_len]);
    extra_index += fields_len;
    const field_value_body_lens: ?[]const u32 = if (small.any_field_values) lens: {
        const lens = zir.extra[extra_index..][0..fields_len];
        extra_index += fields_len;
        break :lens @ptrCast(lens);
    } else null;
    const tag_type_body: ?[]const Zir.Inst.Index = switch (tag_type_body_len) {
        0 => null,
        else => |n| zir.bodySlice(extra_index, n),
    };
    extra_index += tag_type_body_len;
    const field_bodies_overlong: []const Inst.Index = @ptrCast(zir.extra[extra_index..]);
    return .{
        .src_line = extra.data.src_line,
        .src_node = extra.data.src_node,
        .name_strategy = small.name_strategy,
        .captures = captures,
        .capture_names = capture_names,
        .decls = decls,
        .tag_type_body = tag_type_body,
        .nonexhaustive = small.nonexhaustive,
        .field_names = field_names,
        .field_value_body_lens = field_value_body_lens,
        .field_bodies_overlong = field_bodies_overlong,
    };
}
pub const UnwrappedEnumDecl = struct {
    src_line: u32,
    src_node: Ast.Node.Index,
    name_strategy: Inst.NameStrategy,

    captures: []const Inst.Capture,
    capture_names: []const NullTerminatedString,

    decls: []const Inst.Index,

    tag_type_body: ?[]const Inst.Index,
    nonexhaustive: bool,

    field_names: []const NullTerminatedString,
    field_value_body_lens: ?[]const u32,
    field_bodies_overlong: []const Inst.Index,

    pub fn iterateFields(enum_decl: UnwrappedEnumDecl) FieldIterator {
        return .{
            .next_idx = 0,
            .names = enum_decl.field_names,
            .value_body_lens = enum_decl.field_value_body_lens,
            .bodies_overlong = enum_decl.field_bodies_overlong,
        };
    }

    pub const FieldIterator = struct {
        next_idx: u32,
        names: []const NullTerminatedString,
        value_body_lens: ?[]const u32,
        bodies_overlong: []const Inst.Index,
        pub const Field = struct {
            idx: u32,
            name: NullTerminatedString,
            value_body: ?[]const Inst.Index,
        };
        pub fn next(it: *FieldIterator) ?Field {
            const idx = it.next_idx;
            if (idx == it.names.len) return null;
            it.next_idx += 1;
            return .{
                .idx = idx,
                .name = it.names[idx],
                .value_body = it.body(if (it.value_body_lens) |l| l[idx] else 0),
            };
        }
        fn body(it: *FieldIterator, len: u32) ?[]const Inst.Index {
            if (len == 0) return null;
            const b = it.bodies_overlong[0..len];
            it.bodies_overlong = it.bodies_overlong[len..];
            return b;
        }
    };
};

pub fn getOpaqueDecl(zir: *const Zir, opaque_decl: Inst.Index) UnwrappedOpaqueDecl {
    const inst_data = zir.instructions.get(@backingInt(opaque_decl));
    assert(inst_data.tag == .extended);
    assert(inst_data.data.extended.opcode == .opaque_decl);
    const small: Inst.OpaqueDecl.Small = @bitCast(inst_data.data.extended.small);
    const extra = zir.extraData(Inst.OpaqueDecl, inst_data.data.extended.operand);
    var extra_index = extra.end;
    const captures_len: u32 = if (small.has_captures_len) blk: {
        const captures_len = zir.extra[extra_index];
        extra_index += 1;
        break :blk captures_len;
    } else 0;
    const decls_len: u32 = if (small.has_decls_len) blk: {
        const decls_len = zir.extra[extra_index];
        extra_index += 1;
        break :blk decls_len;
    } else 0;
    const captures: []const Inst.Capture = @ptrCast(zir.extra[extra_index..][0..captures_len]);
    extra_index += captures_len;
    const capture_names: []const NullTerminatedString = @ptrCast(zir.extra[extra_index..][0..captures_len]);
    extra_index += captures_len;
    const decls: []const Inst.Index = @ptrCast(zir.extra[extra_index..][0..decls_len]);
    extra_index += decls_len;
    return .{
        .src_line = extra.data.src_line,
        .src_node = extra.data.src_node,
        .name_strategy = small.name_strategy,
        .captures = captures,
        .capture_names = capture_names,
        .decls = decls,
    };
}
pub const UnwrappedOpaqueDecl = struct {
    src_line: u32,
    src_node: Ast.Node.Index,
    name_strategy: Inst.NameStrategy,
    captures: []const Inst.Capture,
    capture_names: []const NullTerminatedString,
    decls: []const Inst.Index,
};