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Merged
boomanaiden154 merged 13 commits into from
Feb 6, 2026
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[Clang] Mark this pointer in destructors dead_on_return #166276

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[Clang] Mark this pointer in destructors dead_on_return
boomanaiden154 Nov 3, 2025
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Test updates
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Merge branch 'main' into clang-destructor-dead-on-return
boomanaiden154 Jan 21, 2026
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update to be sized
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fix test
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Merge branch 'main' into clang-destructor-dead-on-return
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2 changes: 2 additions & 0 deletions clang/include/clang/Basic/CodeGenOptions.def
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Expand Up @@ -189,6 +189,8 @@ CODEGENOPT(EnableSegmentedStacks , 1, 0, Benign) ///< Set when -fsplit-stack is
CODEGENOPT(StackClashProtector, 1, 0, Benign) ///< Set when -fstack-clash-protection is enabled.
CODEGENOPT(NoImplicitFloat , 1, 0, Benign) ///< Set when -mno-implicit-float is enabled.
CODEGENOPT(NullPointerIsValid , 1, 0, Benign) ///< Assume Null pointer deference is defined.
CODEGENOPT(MarkObjectsDeadAfterDestructors , 1, 0, Benign) ///< Assume an object is dead
///< after its destructor returns.
CODEGENOPT(OpenCLCorrectlyRoundedDivSqrt, 1, 0, Benign) ///< -cl-fp32-correctly-rounded-divide-sqrt
CODEGENOPT(HIPCorrectlyRoundedDivSqrt, 1, 1, Benign) ///< -fno-hip-fp32-correctly-rounded-divide-sqrt
CODEGENOPT(DisableBlockSignatureString, 1, 0, Benign) ///< Set when -fdisable-block-signature-string is enabled.
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14 changes: 14 additions & 0 deletions clang/include/clang/Options/Options.td
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Expand Up @@ -2916,6 +2916,20 @@ attribute as undefined behavior. (And, thus the optimizer may assume that any
pointer used in such a way must not have been null and optimize away the
branches accordingly.) On by default.}]>;

defm mark_objects_dead_after_destructors
: BoolFOption<
"mark-objects-dead-after-destructors",
CodeGenOpts<"MarkObjectsDeadAfterDestructors">, DefaultTrue,
NegFlag<SetFalse, [], [ClangOption, CC1Option],
"Do not mark an object dead after its destructor returns">,
PosFlag<SetTrue, [], [ClangOption, CC1Option],
"Mark an object dead after is destructor returns">,
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BothFlags<[], [ClangOption, CLOption]>>,
DocBrief<
[{When enabled, mark an object dead after is destructor returns which allows the
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the optimizer to perform more aggressive optimizations in some cases, particularly dead
store elimination.}]>;

defm use_line_directives : BoolFOption<"use-line-directives",
PreprocessorOutputOpts<"UseLineDirectives">, DefaultFalse,
PosFlag<SetTrue, [], [ClangOption, CC1Option],
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17 changes: 16 additions & 1 deletion clang/lib/CodeGen/CGCall.cpp
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Expand Up @@ -28,6 +28,7 @@
#include "clang/AST/DeclCXX.h"
#include "clang/AST/DeclObjC.h"
#include "clang/Basic/CodeGenOptions.h"
#include "clang/Basic/LLVM.h"
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#include "clang/Basic/TargetInfo.h"
#include "clang/CodeGen/CGFunctionInfo.h"
#include "clang/CodeGen/SwiftCallingConv.h"
Expand Down Expand Up @@ -2767,7 +2768,8 @@ void CodeGenModule::ConstructAttributeList(StringRef Name,
}

// Apply `nonnull`, `dereferenceable(N)` and `align N` to the `this` argument,
// unless this is a thunk function.
// unless this is a thunk function. Add dead_on_return to the `this` argument
// in base class destructors to aid in DSE.
// FIXME: fix this properly, https://reviews.llvm.org/D100388
if (FI.isInstanceMethod() && !IRFunctionArgs.hasInallocaArg() &&
!FI.arg_begin()->type->isVoidPointerType() && !IsThunk) {
Expand Down Expand Up @@ -2800,6 +2802,19 @@ void CodeGenModule::ConstructAttributeList(StringRef Name,
.getAsAlign();
Attrs.addAlignmentAttr(Alignment);

const auto *DD = dyn_cast_if_present<CXXDestructorDecl>(
CalleeInfo.getCalleeDecl().getDecl());
if (DD && CodeGenOpts.MarkObjectsDeadAfterDestructors) {
const CXXRecordDecl *ClassDecl =
dyn_cast<CXXRecordDecl>(DD->getDeclContext());
// TODO(boomanaiden154): We are being intentionally conservative here
// as we gain experience with this optimization. These checks should be
// removed once we have done further integration testing.
if (ClassDecl->getNumBases() == 0 && ClassDecl->getNumVBases() == 0) {

@rnk rnk Dec 1, 2025

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Why do we have to limit this to only destructors of classes with no bases? Whatever the reason (caution, incremental change, etc), comments here would be appreciated.

@rjmccall rjmccall Dec 1, 2025 •
edited
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Virtual base subobjects aren't dead after a base subobject destructor call, but yeah, I can't think of a reason to limit this because of non-virtual bases alone. And even virtual bases are dead after a complete-object destructor call.

@boomanaiden154 boomanaiden154 Dec 2, 2025

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For now, just to be conservative while we get implementation experience. I've added a TODO for myself to remove this after we do more testing.

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Attrs.addAttribute(llvm::Attribute::DeadOnReturn);
}
}

ArgAttrs[IRArgs.first] = llvm::AttributeSet::get(getLLVMContext(), Attrs);
}

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3 changes: 3 additions & 0 deletions clang/lib/Driver/ToolChains/Clang.cpp
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Expand Up @@ -5626,6 +5626,9 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
Args.addOptOutFlag(CmdArgs, options::OPT_fdelete_null_pointer_checks,
options::OPT_fno_delete_null_pointer_checks);

Args.addOptOutFlag(CmdArgs, options::OPT_fmark_objects_dead_after_destructors,
options::OPT_fno_mark_objects_dead_after_destructors);

// LLVM Code Generator Options.

if (Arg *A = Args.getLastArg(options::OPT_mabi_EQ_quadword_atomics)) {
Expand Down
8 changes: 4 additions & 4 deletions clang/test/CodeGen/paren-list-agg-init.cpp
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Expand Up @@ -394,9 +394,9 @@ namespace gh61145 {
// a.k.a. Vec::Vec(Vec&&)
// CHECK-NEXT: call void @_ZN7gh611453VecC1EOS0_(ptr noundef nonnull align 1 dereferenceable(1) [[AGG_TMP_ENSURED]], ptr noundef nonnull align 1 dereferenceable(1) [[V]])
// a.k.a. S1::~S1()
// CHECK-NEXT: call void @_ZN7gh611452S1D1Ev(ptr noundef nonnull align 1 dereferenceable(1) [[AGG_TMP_ENSURED]])
// CHECK-NEXT: call void @_ZN7gh611452S1D1Ev(ptr dead_on_return noundef nonnull align 1 dereferenceable(1) [[AGG_TMP_ENSURED]])
// a.k.a.Vec::~Vec()
// CHECK-NEXT: call void @_ZN7gh611453VecD1Ev(ptr noundef nonnull align 1 dereferenceable(1) [[V]])
// CHECK-NEXT: call void @_ZN7gh611453VecD1Ev(ptr dead_on_return noundef nonnull align 1 dereferenceable(1) [[V]])
// CHECK-NEXT: ret void
template <int I>
void make1() {
Expand All @@ -416,9 +416,9 @@ namespace gh61145 {
// CHECK-NEXT: [[C:%.*c.*]] = getelementptr inbounds nuw [[STRUCT_S2]], ptr [[AGG_TMP_ENSURED]], i32 0, i32
// CHECK-NEXT: store i8 0, ptr [[C]], align 1
// a.k.a. S2::~S2()
// CHECK-NEXT: call void @_ZN7gh611452S2D1Ev(ptr noundef nonnull align 1 dereferenceable(2) [[AGG_TMP_ENSURED]])
// CHECK-NEXT: call void @_ZN7gh611452S2D1Ev(ptr dead_on_return noundef nonnull align 1 dereferenceable(2) [[AGG_TMP_ENSURED]])
// a.k.a. Vec::~Vec()
// CHECK-NEXT: call void @_ZN7gh611453VecD1Ev(ptr noundef nonnull align 1 dereferenceable(1) [[V]])
// CHECK-NEXT: call void @_ZN7gh611453VecD1Ev(ptr dead_on_return noundef nonnull align 1 dereferenceable(1) [[V]])
// CHECK-NEXT: ret void
template <int I>
void make2() {
Expand Down
12 changes: 6 additions & 6 deletions clang/test/CodeGen/temporary-lifetime.cpp
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Expand Up @@ -24,12 +24,12 @@ void Test1() {
// CHECK-DTOR: call void @llvm.lifetime.start.p0(ptr nonnull %[[ADDR:.+]])
// CHECK-DTOR: call void @_ZN1AC1Ev(ptr nonnull {{[^,]*}} %[[VAR:[^ ]+]])
// CHECK-DTOR: call void @_Z3FooIRK1AEvOT_
// CHECK-DTOR: call void @_ZN1AD1Ev(ptr nonnull {{[^,]*}} %[[VAR]])
// CHECK-DTOR: call void @_ZN1AD1Ev(ptr dead_on_return nonnull {{[^,]*}} %[[VAR]])
// CHECK-DTOR: call void @llvm.lifetime.end.p0(ptr nonnull %[[ADDR]])
// CHECK-DTOR: call void @llvm.lifetime.start.p0(ptr nonnull %[[ADDR:.+]])
// CHECK-DTOR: call void @_ZN1AC1Ev(ptr nonnull {{[^,]*}} %[[VAR:[^ ]+]])
// CHECK-DTOR: call void @_Z3FooIRK1AEvOT_
// CHECK-DTOR: call void @_ZN1AD1Ev(ptr nonnull {{[^,]*}} %[[VAR]])
// CHECK-DTOR: call void @_ZN1AD1Ev(ptr dead_on_return nonnull {{[^,]*}} %[[VAR]])
// CHECK-DTOR: call void @llvm.lifetime.end.p0(ptr nonnull %[[ADDR]])
// CHECK-DTOR: }

Expand Down Expand Up @@ -61,9 +61,9 @@ void Test2() {
// CHECK-DTOR: call void @llvm.lifetime.start.p0(ptr nonnull %[[ADDR2:.+]])
// CHECK-DTOR: call void @_ZN1AC1Ev(ptr nonnull {{[^,]*}} %[[VAR2:[^ ]+]])
// CHECK-DTOR: call void @_Z3FooIRK1AEvOT_
// CHECK-DTOR: call void @_ZN1AD1Ev(ptr nonnull {{[^,]*}} %[[VAR2]])
// CHECK-DTOR: call void @_ZN1AD1Ev(ptr dead_on_return nonnull {{[^,]*}} %[[VAR2]])
// CHECK-DTOR: call void @llvm.lifetime.end.p0(ptr nonnull %[[ADDR2]])
// CHECK-DTOR: call void @_ZN1AD1Ev(ptr nonnull {{[^,]*}} %[[VAR1]])
// CHECK-DTOR: call void @_ZN1AD1Ev(ptr dead_on_return nonnull {{[^,]*}} %[[VAR1]])
// CHECK-DTOR: call void @llvm.lifetime.end.p0(ptr nonnull %[[ADDR1]])
// CHECK-DTOR: }

Expand Down Expand Up @@ -155,12 +155,12 @@ void Test7() {
// CHECK-DTOR: call void @llvm.lifetime.start.p0(ptr nonnull %[[ADDR:.+]])
// CHECK-DTOR: call void @_Z3BazI1AET_v({{.*}} %[[SLOT:[^ ]+]])
// CHECK-DTOR: call void @_Z3FooI1AEvOT_({{.*}} %[[SLOT]])
// CHECK-DTOR: call void @_ZN1AD1Ev(ptr nonnull {{[^,]*}} %[[SLOT]])
// CHECK-DTOR: call void @_ZN1AD1Ev(ptr dead_on_return nonnull {{[^,]*}} %[[SLOT]])
// CHECK-DTOR: call void @llvm.lifetime.end.p0(ptr nonnull %[[ADDR]])
// CHECK-DTOR: call void @llvm.lifetime.start.p0(ptr nonnull %[[ADDR:.+]])
// CHECK-DTOR: call void @_Z3BazI1AET_v({{.*}} %[[SLOT:[^ ]+]])
// CHECK-DTOR: call void @_Z3FooI1AEvOT_({{.*}} %[[SLOT]])
// CHECK-DTOR: call void @_ZN1AD1Ev(ptr nonnull {{[^,]*}} %[[SLOT]])
// CHECK-DTOR: call void @_ZN1AD1Ev(ptr dead_on_return nonnull {{[^,]*}} %[[SLOT]])
// CHECK-DTOR: call void @llvm.lifetime.end.p0(ptr nonnull %[[ADDR]])
// CHECK-DTOR: }
Foo(Baz<A>());
Expand Down
2 changes: 1 addition & 1 deletion clang/test/CodeGenCXX/amdgcn-automatic-variable.cpp
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Expand Up @@ -75,7 +75,7 @@ int x;
// CHECK-NEXT: [[A:%.*]] = alloca [[CLASS_A:%.*]], align 4, addrspace(5)
// CHECK-NEXT: [[A_ASCAST:%.*]] = addrspacecast ptr addrspace(5) [[A]] to ptr
// CHECK-NEXT: call void @_ZN1AC1Ev(ptr noundef nonnull align 4 dereferenceable(4) [[A_ASCAST]])
// CHECK-NEXT: call void @_ZN1AD1Ev(ptr noundef nonnull align 4 dereferenceable(4) [[A_ASCAST]])
// CHECK-NEXT: call void @_ZN1AD1Ev(ptr dead_on_return noundef nonnull align 4 dereferenceable(4) [[A_ASCAST]])
// CHECK-NEXT: ret void
//
void func3() {
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6 changes: 3 additions & 3 deletions clang/test/CodeGenCXX/amdgcn-func-arg.cpp
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Expand Up @@ -43,9 +43,9 @@ void func_with_indirect_arg(A a) {
// CHECK-NEXT: call void @llvm.memcpy.p0.p0.i64(ptr align 4 [[AGG_TMP_ASCAST]], ptr align 4 [[A_ASCAST]], i64 4, i1 false)
// CHECK-NEXT: [[AGG_TMP_ASCAST_ASCAST:%.*]] = addrspacecast ptr [[AGG_TMP_ASCAST]] to ptr addrspace(5)
// CHECK-NEXT: call void @_Z22func_with_indirect_arg1A(ptr addrspace(5) noundef [[AGG_TMP_ASCAST_ASCAST]])
// CHECK-NEXT: call void @_ZN1AD1Ev(ptr noundef nonnull align 4 dereferenceable(4) [[AGG_TMP_ASCAST]])
// CHECK-NEXT: call void @_ZN1AD1Ev(ptr dead_on_return noundef nonnull align 4 dereferenceable(4) [[AGG_TMP_ASCAST]])
// CHECK-NEXT: call void @_Z17func_with_ref_argR1A(ptr noundef nonnull align 4 dereferenceable(4) [[A_ASCAST]])
// CHECK-NEXT: call void @_ZN1AD1Ev(ptr noundef nonnull align 4 dereferenceable(4) [[A_ASCAST]])
// CHECK-NEXT: call void @_ZN1AD1Ev(ptr dead_on_return noundef nonnull align 4 dereferenceable(4) [[A_ASCAST]])
// CHECK-NEXT: ret void
//
void test_indirect_arg_auto() {
Expand All @@ -61,7 +61,7 @@ void test_indirect_arg_auto() {
// CHECK-NEXT: call void @llvm.memcpy.p0.p0.i64(ptr align 4 [[AGG_TMP_ASCAST]], ptr align 4 addrspacecast (ptr addrspace(1) @g_a to ptr), i64 4, i1 false)
// CHECK-NEXT: [[AGG_TMP_ASCAST_ASCAST:%.*]] = addrspacecast ptr [[AGG_TMP_ASCAST]] to ptr addrspace(5)
// CHECK-NEXT: call void @_Z22func_with_indirect_arg1A(ptr addrspace(5) noundef [[AGG_TMP_ASCAST_ASCAST]])
// CHECK-NEXT: call void @_ZN1AD1Ev(ptr noundef nonnull align 4 dereferenceable(4) [[AGG_TMP_ASCAST]])
// CHECK-NEXT: call void @_ZN1AD1Ev(ptr dead_on_return noundef nonnull align 4 dereferenceable(4) [[AGG_TMP_ASCAST]])
// CHECK-NEXT: call void @_Z17func_with_ref_argR1A(ptr noundef nonnull align 4 dereferenceable(4) addrspacecast (ptr addrspace(1) @g_a to ptr))
// CHECK-NEXT: ret void
//
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8 changes: 4 additions & 4 deletions clang/test/CodeGenCXX/control-flow-in-stmt-expr.cpp
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Expand Up @@ -217,7 +217,7 @@ void ArrayInit() {
// CHECK: [[ARRAY_DESTROY_BODY2]]:
// CHECK-NEXT: %arraydestroy.elementPast = phi ptr [ %1, %cleanup ], [ %arraydestroy.element, %[[ARRAY_DESTROY_BODY2]] ]
// CHECK-NEXT: %arraydestroy.element = getelementptr inbounds %struct.Printy, ptr %arraydestroy.elementPast, i64 -1
// CHECK-NEXT: call void @_ZN6PrintyD1Ev(ptr noundef nonnull align 8 dereferenceable(8) %arraydestroy.element)
// CHECK-NEXT: call void @_ZN6PrintyD1Ev(ptr dead_on_return noundef nonnull align 8 dereferenceable(8) %arraydestroy.element)
// CHECK-NEXT: %arraydestroy.done = icmp eq ptr %arraydestroy.element, %arr
// CHECK-NEXT: br i1 %arraydestroy.done, label %[[ARRAY_DESTROY_DONE2]], label %[[ARRAY_DESTROY_BODY2]]

Expand Down Expand Up @@ -265,7 +265,7 @@ void ArraySubobjects() {
// CHECK: [[ARRAY_DESTROY_BODY]]:
// CHECK-NEXT: %arraydestroy.elementPast = phi ptr [ %0, %if.then ], [ %arraydestroy.element, %[[ARRAY_DESTROY_BODY]] ]
// CHECK-NEXT: %arraydestroy.element = getelementptr inbounds %struct.Printy, ptr %arraydestroy.elementPast, i64 -1
// CHECK-NEXT: call void @_ZN6PrintyD1Ev(ptr noundef nonnull align 8 dereferenceable(8) %arraydestroy.element)
// CHECK-NEXT: call void @_ZN6PrintyD1Ev(ptr dead_on_return noundef nonnull align 8 dereferenceable(8) %arraydestroy.element)
// CHECK-NEXT: %arraydestroy.done = icmp eq ptr %arraydestroy.element, %arr2
// CHECK-NEXT: br i1 %arraydestroy.done, label %[[ARRAY_DESTROY_DONE]], label %[[ARRAY_DESTROY_BODY]]

Expand All @@ -277,7 +277,7 @@ void ArraySubobjects() {
// CHECK: [[ARRAY_DESTROY_BODY2]]:
// CHECK-NEXT: %arraydestroy.elementPast4 = phi ptr [ %1, %[[ARRAY_DESTROY_DONE]] ], [ %arraydestroy.element5, %[[ARRAY_DESTROY_BODY2]] ]
// CHECK-NEXT: %arraydestroy.element5 = getelementptr inbounds %struct.Printy, ptr %arraydestroy.elementPast4, i64 -1
// CHECK-NEXT: call void @_ZN6PrintyD1Ev(ptr noundef nonnull align 8 dereferenceable(8) %arraydestroy.element5)
// CHECK-NEXT: call void @_ZN6PrintyD1Ev(ptr dead_on_return noundef nonnull align 8 dereferenceable(8) %arraydestroy.element5)
// CHECK-NEXT: %arraydestroy.done6 = icmp eq ptr %arraydestroy.element5, [[ARRAY_BEGIN]]
// CHECK-NEXT: br i1 %arraydestroy.done6, label %[[ARRAY_DESTROY_DONE2:.+]], label %[[ARRAY_DESTROY_BODY2]]

Expand Down Expand Up @@ -384,7 +384,7 @@ void NewArrayInit() {
// CHECK: arraydestroy.body:
// CHECK-NEXT: %arraydestroy.elementPast = phi ptr [ %{{.*}}, %if.then ], [ %arraydestroy.element, %arraydestroy.body ]
// CHECK-NEXT: %arraydestroy.element = getelementptr inbounds %struct.Printy, ptr %arraydestroy.elementPast, i64 -1
// CHECK-NEXT: call void @_ZN6PrintyD1Ev(ptr noundef nonnull align 8 dereferenceable(8) %arraydestroy.element)
// CHECK-NEXT: call void @_ZN6PrintyD1Ev(ptr dead_on_return noundef nonnull align 8 dereferenceable(8) %arraydestroy.element)
// CHECK-NEXT: %arraydestroy.done = icmp eq ptr %arraydestroy.element, %0
// CHECK-NEXT: br i1 %arraydestroy.done, label %arraydestroy.done{{.*}}, label %arraydestroy.body

Expand Down
6 changes: 3 additions & 3 deletions clang/test/CodeGenCXX/cxx2a-destroying-delete.cpp
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Expand Up @@ -41,11 +41,11 @@ void glob_delete_A(A *a) { ::delete a; }
// CHECK: icmp eq ptr %[[a]], null
// CHECK: br i1

// CHECK-ITANIUM: call void @_ZN1AD1Ev(ptr noundef nonnull align 8 dereferenceable(8) %[[a]])
// CHECK-ITANIUM: call void @_ZN1AD1Ev(ptr dead_on_return noundef nonnull align 8 dereferenceable(8) %[[a]])
// CHECK-ITANIUM-NEXT: call void @_ZdlPvm(ptr noundef %[[a]], i64 noundef 8)
// CHECK-MSABI64: call void @"??1A@@QEAA@XZ"(ptr noundef nonnull align 8 dereferenceable(8) %[[a]])
// CHECK-MSABI64: call void @"??1A@@QEAA@XZ"(ptr dead_on_return noundef nonnull align 8 dereferenceable(8) %[[a]])
// CHECK-MSABI64-NEXT: call void @"??3@YAXPEAX_K@Z"(ptr noundef %[[a]], i64 noundef 8)
// CHECK-MSABI32: call x86_thiscallcc void @"??1A@@QAE@XZ"(ptr noundef nonnull align 4 dereferenceable(4) %[[a]])
// CHECK-MSABI32: call x86_thiscallcc void @"??1A@@QAE@XZ"(ptr dead_on_return noundef nonnull align 4 dereferenceable(4) %[[a]])
// CHECK-MSABI32-NEXT: call void @"??3@YAXPAXI@Z"(ptr noundef %[[a]], i32 noundef 4)

struct B {
Expand Down
28 changes: 28 additions & 0 deletions clang/test/CodeGenCXX/destructor-dead-on-return.cpp
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@@ -0,0 +1,28 @@
// RUN: %clang_cc1 -x c++ -emit-llvm -triple x86_64-unknown-linux-gnu -o - %s | FileCheck --check-prefixes=CHECK,CHECK-ENABLED %s
// RUN: %clang_cc1 -x c++ -emit-llvm -triple x86_64-unknown-linux-gnu -fmark-objects-dead-after-destructors -o - %s | FileCheck --check-prefixes=CHECK,CHECK-ENABLED %s
// RUN: %clang_cc1 -x c++ -emit-llvm -triple x86_64-unknown-linux-gnu -fno-mark-objects-dead-after-destructors -o - %s | FileCheck --check-prefixes=CHECK,CHECK-DISABLED %s

// CHECK: define linkonce_odr void @_ZN3barD2Ev(ptr noundef nonnull align 1 dereferenceable(1) %this)
// CHECK-ENABLED: define linkonce_odr void @_ZN3fooD2Ev(ptr dead_on_return noundef nonnull align 1 dereferenceable(1) %this)
// CHECK-DISABLED: define linkonce_odr void @_ZN3fooD2Ev(ptr noundef nonnull align 1 dereferenceable(1) %this)

int dummyFunction();

class foo {
public:
~foo() {
dummyFunction();
}
};

class bar : foo {
public:
~bar() {
dummyFunction();
}
};

int main() {
bar baz;
return 0;
}
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