getIntrinsic

pub fn getIntrinsic(
    self: *Builder,
    id: Intrinsic,
    overload: []const Type,
) Allocator.Error!Function.Index {
    const ExpectedContents = extern union {
        attrs: extern struct {
            params: [expected_args_len]Type,
            fn_attrs: [FunctionAttributes.params_index + expected_args_len]Attributes,
            attrs: [expected_attrs_len]Attribute.Index,
            fields: [expected_fields_len]Type,
        },
    };
    var bfa_buf: ExpectedContents = undefined;
    var bfa: std.heap.BufferFirstAllocator = .init(@ptrCast(&bfa_buf), self.gpa);
    const allocator = bfa.allocator();

    const name = name: {
        {
            var aw: Writer.Allocating = .fromArrayList(self.gpa, &self.strtab_string_bytes);
            const w = &aw.writer;
            defer self.strtab_string_bytes = aw.toArrayList();
            w.print("llvm.{s}", .{@tagName(id)}) catch return error.OutOfMemory;
            for (overload) |ty| w.print(".{f}", .{ty.fmt(self, .m)}) catch return error.OutOfMemory;
        }
        break :name try self.trailingStrtabString();
    };
    if (self.getGlobal(name)) |global| return global.ptrConst(self).kind.function;

    const signature = Intrinsic.signatures.get(id);
    const param_types = try allocator.alloc(Type, signature.params.len);
    defer allocator.free(param_types);
    const function_attributes = try allocator.alloc(
        Attributes,
        FunctionAttributes.params_index + (signature.params.len - signature.ret_len),
    );
    defer allocator.free(function_attributes);

    var attributes: struct {
        builder: *Builder,
        list: std.array_list.Managed(Attribute.Index),

        fn deinit(state: *@This()) void {
            state.list.deinit();
            state.* = undefined;
        }

        fn get(state: *@This(), attributes: []const Attribute) Allocator.Error!Attributes {
            try state.list.resize(attributes.len);
            for (state.list.items, attributes) |*item, attribute|
                item.* = try state.builder.attr(attribute);
            return state.builder.attrs(state.list.items);
        }
    } = .{ .builder = self, .list = std.array_list.Managed(Attribute.Index).init(allocator) };
    defer attributes.deinit();

    var overload_index: usize = 0;
    function_attributes[FunctionAttributes.function_index] = try attributes.get(signature.attrs);
    function_attributes[FunctionAttributes.return_index] = .none; // needed for void return
    for (0.., param_types, signature.params) |param_index, *param_type, signature_param| {
        switch (signature_param.kind) {
            .type => |ty| param_type.* = ty,
            .overloaded => {
                param_type.* = overload[overload_index];
                overload_index += 1;
            },
            .matches, .matches_scalar, .matches_changed_scalar => {},
        }
        function_attributes[
            if (param_index < signature.ret_len)
                FunctionAttributes.return_index
            else
                FunctionAttributes.params_index + (param_index - signature.ret_len)
        ] = try attributes.get(signature_param.attrs);
    }
    assert(overload_index == overload.len);
    for (param_types, signature.params) |*param_type, signature_param| {
        param_type.* = switch (signature_param.kind) {
            .type, .overloaded => continue,
            .matches => |param_index| param_types[param_index],
            .matches_scalar => |param_index| param_types[param_index].scalarType(self),
            .matches_changed_scalar => |info| try param_types[info.index]
                .changeScalar(info.scalar, self),
        };
    }

    const function_index = try self.addFunction(try self.fnType(switch (signature.ret_len) {
        0 => .void,
        1 => param_types[0],
        else => try self.structType(.normal, param_types[0..signature.ret_len]),
    }, param_types[signature.ret_len..], .normal), name, .default);
    function_index.ptr(self).attributes = try self.fnAttrs(function_attributes);
    return function_index;
}