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carbon-lang/toolchain/lower/testdata/interop/cpp/array.carbon
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David Blaikie 4abb6100e7 Define exported C++ thunks in the LLVM function Clang uses for them (#8060) 
Carbon gives the C++ declaration of an exported Carbon thunk an asm
label that
includes the target's global symbol prefix (`_` on Mach-O). Clang names
a
declaration with an asm label `\01<label>` in the IR, so that LLVM uses
the
label verbatim as the symbol name, while Carbon lowered the thunk
definition
under its unprefixed name. Both name the same symbol, but they were
distinct
globals in the IR, so LLVM couldn't see that the C++ calls refer to the
Carbon
definition. That only works while the definition is never discarded.

Mark the Carbon thunk as a `CppThunk` (as described in
`toolchain/docs/check/cpp/thunks.md`), record its C++ declaration in
`clang_decls`, and when lowering the thunk, ask Clang for its function
(creating it if necessary) and define the thunk in that function. This
means
that the thunk and the C++ calls to it always use the same IR global,
with
Clang's name and signature.

The thunk takes all of its parameters by reference, so Clang lowers its
parameters the same way Carbon does, but some C++ ABIs (such as Apple
arm64)
return `this` from constructors. In that case, return the parameter that
Clang
marks `returned`.

On targets without a global prefix, the IR names already matched, so the
only
change is that the thunk definitions now carry Clang's parameter and
function
attributes.
2026-10-30 01:22:12 +00:00

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// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
// Exceptions. See /LICENSE for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
// INCLUDE-FILE: toolchain/testing/testdata/min_prelude/array.carbon
//
// AUTOUPDATE
// TIP: To test this file alone, run:
// TIP: bazel test //toolchain/testing:file_test --test_arg=--file_tests=toolchain/lower/testdata/interop/cpp/array.carbon
// TIP: To dump output, run:
// TIP: bazel run //toolchain/testing:file_test -- --dump_output --file_tests=toolchain/lower/testdata/interop/cpp/array.carbon
// --- array_value_param.carbon
library "[[@TEST_NAME]]";
import Cpp;
fn F(a: array(i32, 5)) -> i32 { return a[2]; }
inline Cpp '''
int G() {
int arr[5];
return Carbon::F(arr);
}
int H() {
return Carbon::F({1, 2, 3, 4, 5});
}
''';
// CHECK:STDOUT: ; ---
// CHECK:STDOUT: ; ModuleID = 'array_value_param.carbon'
// CHECK:STDOUT: source_filename = "array_value_param.carbon"
// CHECK:STDOUT: target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
// CHECK:STDOUT: target triple = "x86_64-unknown-linux-gnu"
// CHECK:STDOUT:
// CHECK:STDOUT: @constinit = private constant [5 x i32] [i32 1, i32 2, i32 3, i32 4, i32 5], align 4
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: mustprogress uwtable
// CHECK:STDOUT: define dso_local noundef i32 @_Z1Gv() #0 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: %arr = alloca [5 x i32], align 16
// CHECK:STDOUT: call void @llvm.lifetime.start.p0(ptr %arr) #3
// CHECK:STDOUT: %call = call noundef i32 @_ZN6Carbon4MainL1FERA5_Ki(ptr noundef nonnull align 4 dereferenceable(20) %arr)
// CHECK:STDOUT: call void @llvm.lifetime.end.p0(ptr %arr) #3
// CHECK:STDOUT: ret i32 %call
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: nocallback nofree nosync nounwind willreturn memory(argmem: readwrite)
// CHECK:STDOUT: declare void @llvm.lifetime.start.p0(ptr captures(none)) #1
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: alwaysinline mustprogress nounwind uwtable
// CHECK:STDOUT: define internal noundef i32 @_ZN6Carbon4MainL1FERA5_Ki(ptr noundef nonnull align 4 dereferenceable(20) %0) #2 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: %retval = alloca i32, align 4
// CHECK:STDOUT: %.addr = alloca ptr, align 8
// CHECK:STDOUT: store ptr %0, ptr %.addr, align 8, !tbaa !48
// CHECK:STDOUT: %1 = load ptr, ptr %.addr, align 8, !tbaa !48, !nonnull !49, !align !50
// CHECK:STDOUT: call void @_CF__carbon_thunk.Main(ptr noundef nonnull align 4 dereferenceable(20) %1, ptr noundef nonnull align 4 dereferenceable(4) %retval)
// CHECK:STDOUT: %2 = load i32, ptr %retval, align 4
// CHECK:STDOUT: ret i32 %2
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: nocallback nofree nosync nounwind willreturn memory(argmem: readwrite)
// CHECK:STDOUT: declare void @llvm.lifetime.end.p0(ptr captures(none)) #1
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: mustprogress uwtable
// CHECK:STDOUT: define dso_local noundef i32 @_Z1Hv() #0 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: %ref.tmp = alloca [5 x i32], align 4
// CHECK:STDOUT: call void @llvm.lifetime.start.p0(ptr %ref.tmp) #3
// CHECK:STDOUT: call void @llvm.memcpy.p0.p0.i64(ptr align 4 %ref.tmp, ptr align 4 @constinit, i64 20, i1 false), !tbaa.struct !3
// CHECK:STDOUT: %call = call noundef i32 @_ZN6Carbon4MainL1FERA5_Ki(ptr noundef nonnull align 4 dereferenceable(20) %ref.tmp)
// CHECK:STDOUT: call void @llvm.lifetime.end.p0(ptr %ref.tmp) #3
// CHECK:STDOUT: ret i32 %call
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: nocallback nofree nosync nounwind willreturn memory(argmem: readwrite)
// CHECK:STDOUT: declare void @llvm.memcpy.p0.p0.i64(ptr noalias writeonly captures(none), ptr noalias readonly captures(none), i64, i1 immarg) #1
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: nounwind
// CHECK:STDOUT: define i32 @_CF.Main(ptr %a) #3 !dbg !32 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: %.loc5_43.2.array.index = getelementptr inbounds [5 x i32], ptr %a, i32 0, i32 2, !dbg !37
// CHECK:STDOUT: %.loc5_43.3 = load i32, ptr %.loc5_43.2.array.index, align 4, !dbg !37
// CHECK:STDOUT: ret i32 %.loc5_43.3, !dbg !38
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: ; Function Attrs: nounwind
// CHECK:STDOUT: define void @_CF__carbon_thunk.Main(ptr noundef nonnull align 4 dereferenceable(20) %_, ptr noundef nonnull align 4 dereferenceable(4) %_1) #4 !dbg !40 {
// CHECK:STDOUT: entry:
// CHECK:STDOUT: %F.call = call i32 @_CF.Main(ptr %_), !dbg !43
// CHECK:STDOUT: store i32 %F.call, ptr %_1, align 4, !dbg !43
// CHECK:STDOUT: ret void, !dbg !43
// CHECK:STDOUT: }
// CHECK:STDOUT:
// CHECK:STDOUT: attributes #0 = { mustprogress uwtable "min-legal-vector-width"="0" "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+cmov,+cx8,+fxsr,+mmx,+sse,+sse2,+x87" "tune-cpu"="generic" }
// CHECK:STDOUT: attributes #1 = { nocallback nofree nosync nounwind willreturn memory(argmem: readwrite) }
// CHECK:STDOUT: attributes #2 = { alwaysinline mustprogress nounwind uwtable "min-legal-vector-width"="0" "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+cmov,+cx8,+fxsr,+mmx,+sse,+sse2,+x87" "tune-cpu"="generic" }
// CHECK:STDOUT: attributes #3 = { nounwind }
// CHECK:STDOUT: attributes #4 = { nounwind "no-trapping-math"="true" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+cmov,+cx8,+fxsr,+mmx,+sse,+sse2,+x87" "tune-cpu"="generic" }
// CHECK:STDOUT:
// CHECK:STDOUT: !llvm.dbg.cu = !{!25}
// CHECK:STDOUT: !llvm.module.flags = !{!51, !52, !53, !6, !7}
// CHECK:STDOUT: !llvm.errno.tbaa = !{!55}
// CHECK:STDOUT:
// CHECK:STDOUT: !0 = !{!"Simple C++ TBAA"}
// CHECK:STDOUT: !1 = !{!"omnipotent char", !0, i64 0}
// CHECK:STDOUT: !2 = !{!1, !1, i64 0}
// CHECK:STDOUT: !3 = !{i64 0, i64 20, !2}
// CHECK:STDOUT: !6 = !{i32 7, !"Dwarf Version", i32 5}
// CHECK:STDOUT: !7 = !{i32 2, !"Debug Info Version", i32 3}
// CHECK:STDOUT: !24 = !DIFile(filename: "array_value_param.carbon", directory: "")
// CHECK:STDOUT: !25 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, file: !24, producer: "carbon", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug)
// CHECK:STDOUT: !26 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
// CHECK:STDOUT: !27 = !DIDerivedType(tag: DW_TAG_pointer_type, baseType: null, size: 64)
// CHECK:STDOUT: !28 = !{!26, !27}
// CHECK:STDOUT: !29 = !DISubroutineType(types: !28)
// CHECK:STDOUT: !30 = !{null, !27, !26}
// CHECK:STDOUT: !31 = !DISubroutineType(types: !30)
// CHECK:STDOUT: !32 = distinct !DISubprogram(name: "F", linkageName: "_CF.Main", scope: null, file: !24, line: 5, type: !29, spFlags: DISPFlagDefinition, unit: !25, retainedNodes: !39)
// CHECK:STDOUT: !33 = !DILocalVariable(arg: 1, scope: !32, type: !27)
// CHECK:STDOUT: !37 = !DILocation(line: 5, column: 40, scope: !32)
// CHECK:STDOUT: !38 = !DILocation(line: 5, column: 33, scope: !32)
// CHECK:STDOUT: !39 = !{!33}
// CHECK:STDOUT: !40 = distinct !DISubprogram(name: "F__carbon_thunk", linkageName: "_CF__carbon_thunk.Main", scope: null, file: !24, line: 5, type: !31, spFlags: DISPFlagDefinition, unit: !25, retainedNodes: !44)
// CHECK:STDOUT: !41 = !DILocalVariable(arg: 1, scope: !40, type: !27)
// CHECK:STDOUT: !42 = !DILocalVariable(arg: 2, scope: !40, type: !26)
// CHECK:STDOUT: !43 = !DILocation(line: 5, column: 1, scope: !40)
// CHECK:STDOUT: !44 = !{!41, !42}
// CHECK:STDOUT: !45 = !{!"int", !1, i64 0}
// CHECK:STDOUT: !46 = !{!"any pointer", !1, i64 0}
// CHECK:STDOUT: !47 = !{!"p1 int", !46, i64 0}
// CHECK:STDOUT: !48 = !{!47, !47, i64 0}
// CHECK:STDOUT: !49 = !{}
// CHECK:STDOUT: !50 = !{i64 4}
// CHECK:STDOUT: !51 = !{i32 8, !"PIC Level", i32 2}
// CHECK:STDOUT: !52 = !{i32 7, !"PIE Level", i32 2}
// CHECK:STDOUT: !53 = !{i32 7, !"uwtable", i32 2}
// CHECK:STDOUT: !54 = !{!"__libc_errno", !45, i64 0}
// CHECK:STDOUT: !55 = !{!54, !45, i64 0}
// CHECK:STDOUT:
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