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[clang][CodeGen] Set dead_on_return when passing arguments indirectly #148159

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Merged
merged 1 commit into from
Jul 18, 2025
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[clang][CodeGen] Set dead_on_return when passing arguments indirectly #148159

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15 changes: 14 additions & 1 deletion clang/lib/CodeGen/CGCall.cpp
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Expand Up @@ -2852,8 +2852,21 @@ void CodeGenModule::ConstructAttributeList(StringRef Name,
if (AI.getInReg())
Attrs.addAttribute(llvm::Attribute::InReg);

if (AI.getIndirectByVal())
// Depending on the ABI, this may be either a byval or a dead_on_return
// argument.
if (AI.getIndirectByVal()) {
Attrs.addByValAttr(getTypes().ConvertTypeForMem(ParamType));
} else {
// Add dead_on_return when the object's lifetime ends in the callee.
// This includes trivially-destructible objects, as well as objects
// whose destruction / clean-up is carried out within the callee (e.g.,
// Obj-C ARC-managed structs, MSVC callee-destroyed objects).
if (!ParamType.isDestructedType() || !ParamType->isRecordType() ||
ParamType->castAs<RecordType>()
->getDecl()
->isParamDestroyedInCallee())
Attrs.addAttribute(llvm::Attribute::DeadOnReturn);
}
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Please use:

  if (!ParamType.isDestructedType() || !ParamType->isRecordType() ||
      ParamType->castAs<RecordType>()->getDecl()->isParamDestroyedInCallee())

We do destroy parameters in the callee in several situations. The most important example is the MSVC C++ ABI, but I believe that coincidentally never uses indirect argument passing, so it wouldn't be testable. The testable example would be something like this in Objective-C++:

struct HasWeakReference {
  __weak id ref;
};
void test(HasWeakReference) {} // should still be dead_on_return because the caller is not responsible to destroy it

__weak helpfully forces the struct to be passed indirectly, but you could also just use a __strong id ref; in a struct that's big enough to be passed indirectly on the target.

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Thank you for clarifying this, updated it. Tests updated too (it indeed looks like from the tests that some MSVC callee-destroyed objects, which are passed indirectly, should be dead_on_return. So is the case for Obj-C++ structs, as mentioned, with __weak and __strong references, as per objc-struct-cxx-abi.mm and ptrauth-struct-cxx-abi.mm tests).


auto *Decl = ParamType->getAsRecordDecl();
if (CodeGenOpts.PassByValueIsNoAlias && Decl &&
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2 changes: 1 addition & 1 deletion clang/test/CodeGen/64bit-swiftcall.c
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Expand Up @@ -239,7 +239,7 @@ TEST(struct_big_1)
// CHECK-LABEL: define {{.*}} void @return_struct_big_1(ptr dead_on_unwind noalias writable sret

// Should not be byval.
// CHECK-LABEL: define {{.*}} void @take_struct_big_1(ptr{{( %.*)?}})
// CHECK-LABEL: define {{.*}} void @take_struct_big_1(ptr dead_on_return{{( %.*)?}})

/*****************************************************************************/
/********************************* TYPE MERGING ******************************/
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16 changes: 8 additions & 8 deletions clang/test/CodeGen/AArch64/byval-temp.c
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Expand Up @@ -30,10 +30,10 @@ void example(void) {
// Then, memcpy `l` to the temporary stack space.
// CHECK-O0-NEXT: call void @llvm.memcpy.p0.p0.i64(ptr align 8 %[[byvaltemp]], ptr align 8 %[[l]], i64 64, i1 false)
// Finally, call using a pointer to the temporary stack space.
// CHECK-O0-NEXT: call void @pass_large(ptr noundef %[[byvaltemp]])
// CHECK-O0-NEXT: call void @pass_large(ptr dead_on_return noundef %[[byvaltemp]])
// Now, do the same for the second call, using the second temporary alloca.
// CHECK-O0-NEXT: call void @llvm.memcpy.p0.p0.i64(ptr align 8 %[[byvaltemp1]], ptr align 8 %[[l]], i64 64, i1 false)
// CHECK-O0-NEXT: call void @pass_large(ptr noundef %[[byvaltemp1]])
// CHECK-O0-NEXT: call void @pass_large(ptr dead_on_return noundef %[[byvaltemp1]])
// CHECK-O0-NEXT: ret void
//
// At O3, we should have lifetime markers to help the optimizer re-use the temporary allocas.
Expand All @@ -58,15 +58,15 @@ void example(void) {
// Then, memcpy `l` to the temporary stack space.
// CHECK-O3-NEXT: call void @llvm.memcpy.p0.p0.i64(ptr align 8 %[[byvaltemp]], ptr align 8 %[[l]], i64 64, i1 false)
// Finally, call using a pointer to the temporary stack space.
// CHECK-O3-NEXT: call void @pass_large(ptr noundef %[[byvaltemp]])
// CHECK-O3-NEXT: call void @pass_large(ptr dead_on_return noundef %[[byvaltemp]])
//
// The lifetime of the temporary used to pass a pointer to the struct ends here.
// CHECK-O3-NEXT: call void @llvm.lifetime.end.p0(i64 64, ptr %[[byvaltemp]])
//
// Now, do the same for the second call, using the second temporary alloca.
// CHECK-O3-NEXT: call void @llvm.lifetime.start.p0(i64 64, ptr %[[byvaltemp1]])
// CHECK-O3-NEXT: call void @llvm.memcpy.p0.p0.i64(ptr align 8 %[[byvaltemp1]], ptr align 8 %[[l]], i64 64, i1 false)
// CHECK-O3-NEXT: call void @pass_large(ptr noundef %[[byvaltemp1]])
// CHECK-O3-NEXT: call void @pass_large(ptr dead_on_return noundef %[[byvaltemp1]])
// CHECK-O3-NEXT: call void @llvm.lifetime.end.p0(i64 64, ptr %[[byvaltemp1]])
//
// Mark the end of the lifetime of `l`.
Expand All @@ -88,12 +88,12 @@ void example_BitInt(void) {
// CHECK-O0-NEXT: [[LOADEDV:%.*]] = trunc i256 [[TMP0]] to i129
// CHECK-O0-NEXT: [[STOREDV:%.*]] = sext i129 [[LOADEDV]] to i256
// CHECK-O0-NEXT: store i256 [[STOREDV]], ptr [[INDIRECT_ARG_TEMP]], align 16
// CHECK-O0-NEXT: call void @pass_large_BitInt(ptr noundef [[INDIRECT_ARG_TEMP]])
// CHECK-O0-NEXT: call void @pass_large_BitInt(ptr dead_on_return noundef [[INDIRECT_ARG_TEMP]])
// CHECK-O0-NEXT: [[TMP1:%.*]] = load i256, ptr [[L]], align 16
// CHECK-O0-NEXT: [[LOADEDV1:%.*]] = trunc i256 [[TMP1]] to i129
// CHECK-O0-NEXT: [[STOREDV1:%.*]] = sext i129 [[LOADEDV1]] to i256
// CHECK-O0-NEXT: store i256 [[STOREDV1]], ptr [[INDIRECT_ARG_TEMP1]], align 16
// CHECK-O0-NEXT: call void @pass_large_BitInt(ptr noundef [[INDIRECT_ARG_TEMP1]])
// CHECK-O0-NEXT: call void @pass_large_BitInt(ptr dead_on_return noundef [[INDIRECT_ARG_TEMP1]])
// CHECK-O0-NEXT: ret void
//
// CHECK-O3-LABEL: define dso_local void @example_BitInt(
Expand All @@ -108,13 +108,13 @@ void example_BitInt(void) {
// CHECK-O3-NEXT: call void @llvm.lifetime.start.p0(i64 32, ptr [[INDIRECT_ARG_TEMP]])
// CHECK-O3-NEXT: [[STOREDV:%.*]] = sext i129 [[LOADEDV]] to i256
// CHECK-O3-NEXT: store i256 [[STOREDV]], ptr [[INDIRECT_ARG_TEMP]], align 16, !tbaa [[TBAA6]]
// CHECK-O3-NEXT: call void @pass_large_BitInt(ptr noundef [[INDIRECT_ARG_TEMP]])
// CHECK-O3-NEXT: call void @pass_large_BitInt(ptr dead_on_return noundef [[INDIRECT_ARG_TEMP]])
// CHECK-O3-NEXT: call void @llvm.lifetime.end.p0(i64 32, ptr [[INDIRECT_ARG_TEMP]])
// CHECK-O3-NEXT: [[TMP1:%.*]] = load i256, ptr [[L]], align 16, !tbaa [[TBAA6]]
// CHECK-O3-NEXT: [[LOADEDV1:%.*]] = trunc i256 [[TMP1]] to i129
// CHECK-O3-NEXT: call void @llvm.lifetime.start.p0(i64 32, ptr [[INDIRECT_ARG_TEMP1]])
// CHECK-O3-NEXT: [[STOREDV1:%.*]] = sext i129 [[LOADEDV1]] to i256
// CHECK-O3-NEXT: store i256 [[STOREDV1]], ptr [[INDIRECT_ARG_TEMP1]], align 16, !tbaa [[TBAA6]]
// CHECK-O3-NEXT: call void @pass_large_BitInt(ptr noundef [[INDIRECT_ARG_TEMP1]])
// CHECK-O3-NEXT: call void @pass_large_BitInt(ptr dead_on_return noundef [[INDIRECT_ARG_TEMP1]])
// CHECK-O3-NEXT: call void @llvm.lifetime.end.p0(i64 32, ptr [[INDIRECT_ARG_TEMP1]])
// CHECK-O3-NEXT: call void @llvm.lifetime.end.p0(i64 32, ptr [[L]])
2 changes: 1 addition & 1 deletion clang/test/CodeGen/AArch64/pure-scalable-args-empty-union.c
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Expand Up @@ -19,7 +19,7 @@ void f0(S0 *p) {
use0(*p);
}
// CHECK-C: declare void @use0(<vscale x 4 x float>, <vscale x 4 x float>, <vscale x 4 x float>, <vscale x 4 x float>)
// CHECK-CXX: declare void @use0(ptr noundef)
// CHECK-CXX: declare void @use0(ptr dead_on_return noundef)

#ifdef __cplusplus

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