comptimeExpr2

fn comptimeExpr2(
    gz: *GenZir,
    scope: *Scope,
    ri: ResultInfo,
    node: Ast.Node.Index,
    src_node: Ast.Node.Index,
    reason: std.zig.SimpleComptimeReason,
) InnerError!Zir.Inst.Ref {
    if (gz.is_comptime) {
        // No need to change anything!
        return expr(gz, scope, ri, node);
    }

    // There's an optimization here: if the body will be evaluated at comptime regardless, there's
    // no need to wrap it in a block. This is hard to determine in general, but we can identify a
    // common subset of trivially comptime expressions to take down the size of the ZIR a bit.
    const tree = gz.astgen.tree;
    switch (tree.nodeTag(node)) {
        .identifier => {
            // Many identifiers can be handled without a `block_comptime`, so `AstGen.identifier` has
            // special handling for this case.
            return identifier(gz, scope, ri, node, .{ .src_node = src_node, .reason = reason });
        },

        // These are leaf nodes which are always comptime-known.
        .number_literal,
        .char_literal,
        .string_literal,
        .multiline_string_literal,
        .enum_literal,
        .error_value,
        .anyframe_literal,
        .error_set_decl,
        // These nodes are not leaves, but will force comptime evaluation of all sub-expressions, and
        // hence behave the same regardless of whether they're in a comptime scope.
        .error_union,
        .merge_error_sets,
        .optional_type,
        .anyframe_type,
        .ptr_type_aligned,
        .ptr_type_sentinel,
        .ptr_type,
        .ptr_type_bit_range,
        .array_type,
        .array_type_sentinel,
        .fn_proto_simple,
        .fn_proto_multi,
        .fn_proto_one,
        .fn_proto,
        .container_decl,
        .container_decl_trailing,
        .container_decl_arg,
        .container_decl_arg_trailing,
        .container_decl_two,
        .container_decl_two_trailing,
        .tagged_union,
        .tagged_union_trailing,
        .tagged_union_enum_tag,
        .tagged_union_enum_tag_trailing,
        .tagged_union_two,
        .tagged_union_two_trailing,
        => {
            // No need to worry about result location here, we're not creating a comptime block!
            return expr(gz, scope, ri, node);
        },

        // Lastly, for labelled blocks, avoid emitting a labelled block directly inside this
        // comptime block, because that would be silly! Note that we don't bother doing this for
        // unlabelled blocks, since they don't generate blocks at comptime anyway (see `blockExpr`).
        .block_two, .block_two_semicolon, .block, .block_semicolon => {
            const lbrace = tree.nodeMainToken(node);
            // Careful! We can't pass in the real result location here, since it may
            // refer to runtime memory. A runtime-to-comptime boundary has to remove
            // result location information, compute the result, and copy it to the true
            // result location at runtime. We do this below as well.
            const ty_only_ri: ResultInfo = .{
                .ctx = ri.ctx,
                .rl = if (try ri.rl.resultType(gz, node)) |res_ty|
                    .{ .coerced_ty = res_ty }
                else
                    .none,
            };
            if (tree.isTokenPrecededByTags(lbrace, &.{ .identifier, .colon })) {
                var buf: [2]Ast.Node.Index = undefined;
                const stmts = tree.blockStatements(&buf, node).?;

                // Replace result location and copy back later - see above.
                const block_ref = try labeledBlockExpr(gz, scope, ty_only_ri, node, stmts, true, .normal);
                return rvalue(gz, ri, block_ref, node);
            }
        },

        // In other cases, we don't optimize anything - we need a wrapper comptime block.
        else => {},
    }

    var block_scope = gz.makeSubBlock(scope);
    block_scope.is_comptime = true;
    defer block_scope.unstack();

    const block_inst = try gz.makeBlockInst(.block_comptime, src_node);
    // Replace result location and copy back later - see above.
    const ty_only_ri: ResultInfo = .{
        .ctx = ri.ctx,
        .rl = if (try ri.rl.resultType(gz, src_node)) |res_ty|
            .{ .coerced_ty = res_ty }
        else
            .none,
    };
    const block_result = try fullBodyExpr(&block_scope, scope, ty_only_ri, node, .normal);
    if (!gz.refIsNoReturn(block_result)) {
        _ = try block_scope.addBreak(.break_inline, block_inst, block_result);
    }
    try block_scope.setBlockComptimeBody(block_inst, reason);
    try gz.instructions.append(gz.astgen.gpa, block_inst);

    return rvalue(gz, ri, block_inst.toRef(), src_node);
}