Emit const globals with constexpr destructor as constant LLVM values

[hans]

Summary

This follows 2b4fa53 which made Clang not emit destructor calls for such objects. However, they would still not get emitted as constants since CodeGenModule::isTypeConstant() only checked whether the destructor was trivial, not if it's constexpr.

Fixes Issue #61212

[hans]

+aaron.ballman

[ilya-biryukov]

I don't have a lot of experience in codegen, so will let Aaron and Richard do the review.

However, still wanted to share one observation. The actual check that avoids emitting the destructors for variables seems more involved than just checking if the destructor is constexpr.
Is it safe to rely solely on the type for codegen? E.g. I would have expected checks that look at HasConstantDestruction for variables with non-trivial constructors.

[hans]

In D145369#4181296, @ilya-biryukov wrote:

I don't have a lot of experience in codegen, so will let Aaron and Richard do the review.

Thanks for checking! I don't have a lot of experience here either, so any review is much appreciated.

However, still wanted to share one observation. The actual check that avoids emitting the destructors for variables seems more involved than just checking if the destructor is constexpr.
Is it safe to rely solely on the type for codegen? E.g. I would have expected checks that look at HasConstantDestruction for variables with non-trivial constructors.

Right, codegen is also factoring in the check about emitting destructors when deciding about marking the LLVM value constant or not:

in CodeGenModule::EmitGlobalVarDefinition()

  bool NeedsGlobalDtor =
      !IsDefinitionAvailableExternally &&
      D->needsDestruction(getContext()) == QualType::DK_cxx_destructor;

...

  // If it is safe to mark the global 'constant', do so now.
  GV->setConstant(!NeedsGlobalCtor && !NeedsGlobalDtor &&
                  isTypeConstant(D->getType(), true));

So I *think* this is correct, and that the hasConstexprDestructor() case was just missing from isTypeConstant() because constexpr destructors were added later. But again, not super familiar with this stuff :)

[aaron.ballman]

This seems reasonable to me, but adding the codegen code owners in case they disagree.

[efriedma]

There appear to be 8 different places that call isTypeConstant(Ty, true); I'd like to see testcases for all of them if it's relevant. (I agree with your assessment for global variables, but not sure about the other places.)

[hans]

Thanks for the review!

Added tests to cover other calls that change behavior due to this.

Please take another look.

[efriedma]

clang/test/CodeGenCXX/static-init.cpp

181

I don't see how this works. For a static local variable, in general, we register the destructor with __cxa_atexit, and the destructor can have arbitrary side-effects. For example:

extern void foo();
struct A {
  constexpr A() : x(1) {}
  constexpr ~A() {if (x) foo();}
  int x;
};
const int *f() {
  static const A a{};
  return &a.x;
}

[efriedma]

clang/lib/CodeGen/CodeGenModule.cpp

4345

For the purposes of CodeGen, checking Record->hasConstexprDestructor() isn't really helpful. Even if Record->hasConstexprDestructor() is true, a destructor can still have side-effects. Since the callers need to handle that possibility anyway, you might as well just skip the Record->hasTrivialDestructor() || Record->hasConstexprDestructor() check.

[hans]

clang/lib/CodeGen/CodeGenModule.cpp

4345

Maybe what we want is to also have an ExcludeDtor param that callers which have checked that no dtor call is needed could set?

clang/test/CodeGenCXX/static-init.cpp

181

Hmm, I guess I assumed the destructor being constexpr meant it wouldn't have side effects, which of course isn't necessarily true.. thanks for the example.

[hans]

Passing a ExcludeDtor param.

[efriedma]

LGTM

clang/lib/CodeGen/CGExprAgg.cpp

535

I'm not sure why we're querying isTypeConstant here? The global shouldn't get written to in any case. But I guess that's a separate issue.

[hans]

clang/lib/CodeGen/CGExprAgg.cpp

535

Yeah, it seems safe to always make the global const. Doing that here: https://reviews.llvm.org/D146211

clang/lib/CodeGen/CGDecl.cpp

if (GV->getValueType() != Init->getType()) {
     llvm::Constant *NewPtrForOldDecl =
     llvm::ConstantExpr::getBitCast(GV, OldGV->getType());
     OldGV->replaceAllUsesWith(NewPtrForOldDecl);
 
     // Erase the old global, since it is no longer used.
     OldGV->eraseFromParent();
   }
 
-  GV->setConstant(CGM.isTypeConstant(D.getType(), true));
+  bool NeedsDtor =
+      D.needsDestruction(getContext()) == QualType::DK_cxx_destructor;
+
+  GV->setConstant(CGM.isTypeConstant(D.getType(), true, !NeedsDtor));
   GV->setInitializer(Init);
 
   emitter.finalize(GV);
 
-  if (D.needsDestruction(getContext()) == QualType::DK_cxx_destructor &&
-      HaveInsertPoint()) {
+  if (NeedsDtor && HaveInsertPoint()) {
     // We have a constant initializer, but a nontrivial destructor. We still
     // need to perform a guarded "initialization" in order to register the
     // destructor.
     EmitCXXGuardedInit(D, GV, /*PerformInit*/false);
   }
 
   return GV;
 }
if (D.getInit() && (Ty->isArrayType() || Ty->isRecordType()) &&
            getContext().getBaseElementType(Ty)->isObjCObjectPointerType()) &&
           D.getInit()->isConstantInitializer(getContext(), false)))) {
 
       // If the variable's a const type, and it's neither an NRVO
       // candidate nor a __block variable and has no mutable members,
       // emit it as a global instead.
       // Exception is if a variable is located in non-constant address space
       // in OpenCL.
+      bool NeedsDtor =
+          D.needsDestruction(getContext()) == QualType::DK_cxx_destructor;
       if ((!getLangOpts().OpenCL ||
            Ty.getAddressSpace() == LangAS::opencl_constant) &&
           (CGM.getCodeGenOpts().MergeAllConstants && !NRVO &&
-           !isEscapingByRef && CGM.isTypeConstant(Ty, true))) {
+           !isEscapingByRef && CGM.isTypeConstant(Ty, true, !NeedsDtor))) {
         EmitStaticVarDecl(D, llvm::GlobalValue::InternalLinkage);
 
         // Signal this condition to later callbacks.
         emission.Addr = Address::invalid();
         assert(emission.wasEmittedAsGlobal());
         return emission;
       }
 

clang/lib/CodeGen/CGDeclCXX.cpp

void CodeGenFunction::EmitCXXGlobalVarDeclInit(const VarDecl &D,
 
   if (!T->isReferenceType()) {
     if (getLangOpts().OpenMP && !getLangOpts().OpenMPSimd &&
         D.hasAttr<OMPThreadPrivateDeclAttr>()) {
       (void)CGM.getOpenMPRuntime().emitThreadPrivateVarDefinition(
           &D, DeclAddr, D.getAttr<OMPThreadPrivateDeclAttr>()->getLocation(),
           PerformInit, this);
     }
+    bool NeedsDtor =
+        D.needsDestruction(getContext()) == QualType::DK_cxx_destructor;
     if (PerformInit)
       EmitDeclInit(*this, D, DeclAddr);
-    if (CGM.isTypeConstant(D.getType(), true))
+    if (CGM.isTypeConstant(D.getType(), true, !NeedsDtor))
       EmitDeclInvariant(*this, D, DeclPtr);
     else
       EmitDeclDestroy(*this, D, DeclAddr);
     return;
   }
 
   assert(PerformInit && "cannot have constant initializer which needs "
          "destruction for reference");

clang/lib/CodeGen/CGExpr.cpp

static Address createReferenceTemporary(CodeGenFunction &CGF,
   case SD_Automatic: {
     // If we have a constant temporary array or record try to promote it into a
     // constant global under the same rules a normal constant would've been
     // promoted. This is easier on the optimizer and generally emits fewer
     // instructions.
     QualType Ty = Inner->getType();
     if (CGF.CGM.getCodeGenOpts().MergeAllConstants &&
         (Ty->isArrayType() || Ty->isRecordType()) &&
-        CGF.CGM.isTypeConstant(Ty, true))
+        CGF.CGM.isTypeConstant(Ty, true, false))
       if (auto Init = ConstantEmitter(CGF).tryEmitAbstract(Inner, Ty)) {
         auto AS = CGF.CGM.GetGlobalConstantAddressSpace();
         auto *GV = new llvm::GlobalVariable(
             CGF.CGM.getModule(), Init->getType(), /*isConstant=*/true,
             llvm::GlobalValue::PrivateLinkage, Init, ".ref.tmp", nullptr,
             llvm::GlobalValue::NotThreadLocal,
             CGF.getContext().getTargetAddressSpace(AS));
         CharUnits alignment = CGF.getContext().getTypeAlignInChars(Ty);

clang/lib/CodeGen/CGExprAgg.cpp

if (NumInitElements * elementSize.getQuantity() > 16 &&
       elementType.isTriviallyCopyableType(CGF.getContext())) {
     CodeGen::CodeGenModule &CGM = CGF.CGM;
     ConstantEmitter Emitter(CGF);
     LangAS AS = ArrayQTy.getAddressSpace();
     if (llvm::Constant *C =
             Emitter.tryEmitForInitializer(ExprToVisit, AS, ArrayQTy)) {
       auto GV = new llvm::GlobalVariable(
           CGM.getModule(), C->getType(),
-          CGM.isTypeConstant(ArrayQTy, /* ExcludeCtorDtor= */ true),
+          CGM.isTypeConstant(ArrayQTy, /* ExcludeCtor= */ true,
+                             /* ExcludeDtor= */ false),
           llvm::GlobalValue::PrivateLinkage, C, "constinit",
           /* InsertBefore= */ nullptr, llvm::GlobalVariable::NotThreadLocal,
           CGM.getContext().getTargetAddressSpace(AS));
       Emitter.finalize(GV);
       CharUnits Align = CGM.getContext().getTypeAlignInChars(ArrayQTy);
       GV->setAlignment(Align.getAsAlign());
       Address GVAddr(GV, GV->getValueType(), Align);
       EmitFinalDestCopy(ArrayQTy, CGF.MakeAddrLValue(GVAddr, ArrayQTy));

clang/lib/CodeGen/CGExprConstant.cpp

tryEmitGlobalCompoundLiteral(ConstantEmitter &emitter,
   llvm::Constant *C = emitter.tryEmitForInitializer(E->getInitializer(),
                                                     addressSpace, E->getType());
   if (!C) {
     assert(!E->isFileScope() &&
            "file-scope compound literal did not have constant initializer!");
     return ConstantAddress::invalid();
   }
 
-  auto GV = new llvm::GlobalVariable(CGM.getModule(), C->getType(),
-                                     CGM.isTypeConstant(E->getType(), true),
-                                     llvm::GlobalValue::InternalLinkage,
-                                     C, ".compoundliteral", nullptr,
-                                     llvm::GlobalVariable::NotThreadLocal,
-                    CGM.getContext().getTargetAddressSpace(addressSpace));
+  auto GV = new llvm::GlobalVariable(
+      CGM.getModule(), C->getType(),
+      CGM.isTypeConstant(E->getType(), true, false),
+      llvm::GlobalValue::InternalLinkage, C, ".compoundliteral", nullptr,
   emitter.finalize(GV);
   GV->setAlignment(Align.getAsAlign());
   CGM.setAddrOfConstantCompoundLiteral(E, GV);
   return ConstantAddress(GV, GV->getValueType(), Align);
 }
 
 static llvm::Constant *
 EmitArrayConstant(CodeGenModule &CGM, llvm::ArrayType *DesiredType,

clang/lib/CodeGen/CodeGenModule.h

public:
   /// getTBAAInfoForSubobject - Get TBAA information for an access with a given
   /// base lvalue.
   TBAAAccessInfo getTBAAInfoForSubobject(LValue Base, QualType AccessType) {
     if (Base.getTBAAInfo().isMayAlias())
       return TBAAAccessInfo::getMayAliasInfo();
     return getTBAAAccessInfo(AccessType);
   }
 
-  bool isTypeConstant(QualType QTy, bool ExcludeCtorDtor);
+  bool isTypeConstant(QualType QTy, bool ExcludeCtor, bool ExcludeDtor);
 
   bool isPaddedAtomicType(QualType type);
   bool isPaddedAtomicType(const AtomicType *type);
 
   /// DecorateInstructionWithTBAA - Decorate the instruction with a TBAA tag.
   void DecorateInstructionWithTBAA(llvm::Instruction *Inst,
                                    TBAAAccessInfo TBAAInfo);
 

clang/lib/CodeGen/CodeGenModule.cpp

if (CXX20ModuleInits && VD->getOwningModule() &&
       // as part of the initializer for an imported one.
       return false;
     }
   }
   // If OpenMP is enabled and threadprivates must be generated like TLS, delay
   // codegen for global variables, because they may be marked as threadprivate.
   if (LangOpts.OpenMP && LangOpts.OpenMPUseTLS &&
       getContext().getTargetInfo().isTLSSupported() && isa<VarDecl>(Global) &&
-      !isTypeConstant(Global->getType(), false) &&
+      !isTypeConstant(Global->getType(), false, false) &&
       !OMPDeclareTargetDeclAttr::isDeclareTargetDeclaration(Global))
     return false;
 
   return true;
 }
 
 ConstantAddress CodeGenModule::GetAddrOfMSGuidDecl(const MSGuidDecl *GD) {
   StringRef Name = getMangledName(GD);
CodeGenModule::CreateRuntimeFunction(llvm::FunctionType *FTy, StringRef Name,
   return {FTy, C};
 }
 
 /// isTypeConstant - Determine whether an object of this type can be emitted
 /// as a constant.
 ///
 /// If ExcludeCtor is true, the duration when the object's constructor runs
 /// will not be considered. The caller will need to verify that the object is
-/// not written to during its construction.
-bool CodeGenModule::isTypeConstant(QualType Ty, bool ExcludeCtor) {
+/// not written to during its construction. ExcludeDtor works similarly.
+bool CodeGenModule::isTypeConstant(QualType Ty, bool ExcludeCtor,
+                                   bool ExcludeDtor) {
   if (!Ty.isConstant(Context) && !Ty->isReferenceType())
     return false;
 
   if (Context.getLangOpts().CPlusPlus) {
     if (const CXXRecordDecl *Record
           = Context.getBaseElementType(Ty)->getAsCXXRecordDecl())
       return ExcludeCtor && !Record->hasMutableFields() &&
-             Record->hasTrivialDestructor();
+             (Record->hasTrivialDestructor() || ExcludeDtor);
   }
 
   return true;
 }
 
 /// GetOrCreateLLVMGlobal - If the specified mangled name is not in the module,
 /// create and return an llvm GlobalVariable with the specified type and address
 /// space. If there is something in the module with the specified name, return
 /// it potentially bitcasted to the right type.
CodeGenModule::GetOrCreateLLVMGlobal(StringRef MangledName, llvm::Type *Ty,
 
   // Handle things which are present even on external declarations.
   if (D) {
     if (LangOpts.OpenMP && !LangOpts.OpenMPSimd)
       getOpenMPRuntime().registerTargetGlobalVariable(D, GV);
 
     // FIXME: This code is overly simple and should be merged with other global
     // handling.
-    GV->setConstant(isTypeConstant(D->getType(), false));
+    GV->setConstant(isTypeConstant(D->getType(), false, false));
 
     GV->setAlignment(getContext().getDeclAlign(D).getAsAlign());
 
     setLinkageForGV(GV, D);
 
     if (D->getTLSKind()) {
       if (D->getTLSKind() == VarDecl::TLS_Dynamic)
         CXXThreadLocals.push_back(D);
#endif
   }
 
   GV->setInitializer(Init);
   if (emitter)
     emitter->finalize(GV);
 
   // If it is safe to mark the global 'constant', do so now.
   GV->setConstant(!NeedsGlobalCtor && !NeedsGlobalDtor &&
-                  isTypeConstant(D->getType(), true));
+                  isTypeConstant(D->getType(), true, true));
 
   // If it is in a read-only section, mark it 'constant'.
   if (const SectionAttr *SA = D->getAttr<SectionAttr>()) {
     const ASTContext::SectionInfo &SI = Context.SectionInfos[SA->getName()];
     if ((SI.SectionFlags & ASTContext::PSF_Write) == 0)
       GV->setConstant(true);
   }
 
ConstantAddress CodeGenModule::GetAddrOfGlobalTemporary(
   llvm::Constant *InitialValue = nullptr;
   bool Constant = false;
   llvm::Type *Type;
   if (Value) {
     // The temporary has a constant initializer, use it.
     emitter.emplace(*this);
     InitialValue = emitter->emitForInitializer(*Value, AddrSpace,
                                                MaterializedType);
-    Constant = isTypeConstant(MaterializedType, /*ExcludeCtor*/Value);
+    Constant = isTypeConstant(MaterializedType, /*ExcludeCtor*/ Value,
+                              /*ExcludeDtor*/ false);
     Type = InitialValue->getType();
   } else {
     // No initializer, the initialization will be provided when we
     // initialize the declaration which performed lifetime extension.
     Type = getTypes().ConvertTypeForMem(MaterializedType);
   }
 
   // Create a global variable for this lifetime-extended temporary.

clang/lib/CodeGen/TargetInfo.cpp

if (!D)
     return DefaultGlobalAS;
 
   LangAS AddrSpace = D->getType().getAddressSpace();
   assert(AddrSpace == LangAS::Default || isTargetAddressSpace(AddrSpace));
   if (AddrSpace != LangAS::Default)
     return AddrSpace;
 
   // Only promote to address space 4 if VarDecl has constant initialization.
-  if (CGM.isTypeConstant(D->getType(), false) &&
+  if (CGM.isTypeConstant(D->getType(), false, false) &&
       D->hasConstantInitialization()) {
     if (auto ConstAS = CGM.getTarget().getConstantAddressSpace())
       return *ConstAS;
   }
   return DefaultGlobalAS;
 }
 
 llvm::SyncScope::ID

clang/test/CodeGenCXX/const-init-cxx11.cpp

 // RUN: %clang_cc1 -no-opaque-pointers -w -fmerge-all-constants -triple x86_64-elf-gnu -emit-llvm -o - %s -std=c++11 | FileCheck %s
+// RUN: %clang_cc1 -no-opaque-pointers -w -fmerge-all-constants -triple x86_64-elf-gnu -emit-llvm -o - %s -std=c++20 | FileCheck -check-prefix=CHECK20 %s
 
 // FIXME: The padding in all these objects should be zero-initialized.
 namespace StructUnion {
   struct A {
     int n;
     double d;
     union U {
       constexpr U(int x) : x(x) {}

 // CHECK: @_ZZN12LocalVarInit3aggEvE1a = internal constant {{.*}} i32 101
 // CHECK: @_ZZN12LocalVarInit4ctorEvE1a = internal constant {{.*}} i32 102
 // CHECK: @__const._ZN12LocalVarInit8mutable_Ev.a = private unnamed_addr constant {{.*}} i32 103
 // CHECK: @_ZGRN33ClassTemplateWithStaticDataMember1SIvE1aE_ = linkonce_odr constant i32 5, comdat
 // CHECK: @_ZN33ClassTemplateWithStaticDataMember3useE ={{.*}} constant i32* @_ZGRN33ClassTemplateWithStaticDataMember1SIvE1aE_
 // CHECK: @_ZGRN39ClassTemplateWithHiddenStaticDataMember1SIvE1aE_ = linkonce_odr hidden constant i32 5, comdat
 // CHECK: @_ZN39ClassTemplateWithHiddenStaticDataMember3useE ={{.*}} constant i32* @_ZGRN39ClassTemplateWithHiddenStaticDataMember1SIvE1aE_
 // CHECK: @_ZGRZN20InlineStaticConstRef3funEvE1i_ = linkonce_odr constant i32 10, comdat
+// CHECK20: @_ZZN12LocalVarInit4dtorEvE1a = internal constant {{.*}} i32 103
 
 // Constant initialization tests go before this point,
 // dynamic initialization tests go after.
 
 // We must emit a constant initializer for NonLiteralConstexpr::ntd, but also
 // emit an initializer to register its destructor.
 // CHECK: define {{.*}}cxx_global_var_init{{.*}}
 // CHECK-NOT: NonLiteralConstexpr
namespace LocalVarInit {
   // CHECK: define {{.*}} @_ZN12LocalVarInit8mutable_Ev
   // CHECK-NOT: call
   // CHECK: call {{.*}}memcpy{{.*}} @__const._ZN12LocalVarInit8mutable_Ev.a
   // CHECK-NOT: call
   // Can't fold return value due to 'mutable'.
   // CHECK-NOT: ret i32 103
   // CHECK: }
   int mutable_() { constexpr Mutable a = { f(103) }; return a.k; }
+
+#if __cplusplus >= 202002L
+  // CHECK20: define {{.*}} @_ZN12LocalVarInit4dtorEv
+  // CHECK20-NOT: call
+  // CHECK20: ret i32 103
+  struct Dtor { constexpr Dtor(int n) : k(n) {} constexpr ~Dtor() {} int k; };
+  int dtor() { constexpr Dtor a = { f(103) }; return a.k; }
+#endif
 }
 
 namespace CrossFuncLabelDiff {
   // Make sure we refuse to constant-fold the variable b.
   constexpr long a(bool x) { return x ? 0 : (long)&&lbl + (0 && ({lbl: 0;})); }
   void test() { static long b = (long)&&lbl - a(false); lbl: return; }
   // CHECK: sub nsw i64 ptrtoint (i8* blockaddress(@_ZN18CrossFuncLabelDiff4testEv, {{.*}}) to i64),
   // CHECK: store i64 {{.*}}, i64* @_ZZN18CrossFuncLabelDiff4testEvE1b, align 8

clang/test/CodeGenCXX/const-init-cxx2a.cpp

 // RUN: %clang_cc1 -triple x86_64-linux-gnu -emit-llvm -o - %s -std=c++2a | FileCheck %s --implicit-check-not=cxx_global_var_init --implicit-check-not=cxa_atexit
 
 // RUN: %clang_cc1 -triple x86_64-linux-gnu -emit-pch -o %t.pch %s -std=c++2a
 // RUN: %clang_cc1 -triple x86_64-linux-gnu -include-pch %t.pch -x c++ /dev/null -emit-llvm -o - -std=c++2a | FileCheck %s --implicit-check-not=cxx_global_var_init --implicit-check-not=cxa_atexit
 
 // CHECK: @a ={{.*}} global i32 123,
 int a = (delete new int, 123);
 
 struct B {
   constexpr B() {}
   constexpr ~B() { n *= 5; }
   int n = 123;
 };
-// CHECK: @b ={{.*}} global {{.*}} i32 123
+// CHECK: @b ={{.*}} constant {{.*}} i32 123
 extern constexpr B b = B();
 
-// CHECK: @_ZL1c = internal global {{.*}} i32 123
+// CHECK: @_ZL1c = internal constant {{.*}} i32 123
 const B c;
 int use_c() { return c.n; }
 
 struct D {
   int n;
   constexpr ~D() {}
 };
 D d;

clang/test/CodeGenCXX/init-invariant.cpp

-// RUN: %clang_cc1 -triple i686-linux-gnu -emit-llvm %s -disable-llvm-passes -o - | FileCheck %s --check-prefix=CHECK-O0
-// RUN: %clang_cc1 -triple i686-linux-gnu -emit-llvm %s -O1 -disable-llvm-passes -o - | FileCheck %s
+// RUN: %clang_cc1 -triple i686-linux-gnu -std=c++20 -emit-llvm %s -disable-llvm-passes -o - | FileCheck %s --check-prefix=CHECK-O0
+// RUN: %clang_cc1 -triple i686-linux-gnu -std=c++20 -emit-llvm %s -O1 -disable-llvm-passes -o - | FileCheck %s
 
 // Check that we add an llvm.invariant.start.p0i8 to mark when a global becomes
 // read-only. If globalopt can fold the initializer, it will then mark the
 // variable as constant.
 
 // Do not produce markers at -O0.
 // CHECK-O0-NOT: llvm.invariant.start.p0i8
 
 struct A {
   A();
   int n;
 };
 
 // CHECK: @a ={{.*}} global {{.*}} zeroinitializer
 extern const A a = A();
 
+struct A2 {
+  A2();
+  constexpr ~A2() {}
+  int n;
+};
+
+// CHECK: @a2 ={{.*}} global {{.*}} zeroinitializer
+extern const A2 a2 = A2();
+
+
 struct B {
   B();
   mutable int n;
 };
 
 // CHECK: @b ={{.*}} global {{.*}} zeroinitializer
 extern const B b = B();
 

 
 void e() {
   static const A a = A();
 }
 
 // CHECK: call void @_ZN1AC1Ev(ptr noundef {{[^,]*}} @a)
 // CHECK: call {{.*}}@llvm.invariant.start.p0(i64 4, ptr @a)
 
+// CHECK: call void @_ZN2A2C1Ev(ptr noundef {{[^,]*}} @a2)
+// CHECK: call {{.*}}@llvm.invariant.start.p0(i64 4, ptr @a2)
+
 // CHECK: call void @_ZN1BC1Ev(ptr noundef {{[^,]*}} @b)
 // CHECK-NOT: call {{.*}}@llvm.invariant.start.p0(i64 noundef 4, ptr @b)
 
 // CHECK: call void @_ZN1CC1Ev(ptr noundef {{[^,]*}} @c)
 // CHECK-NOT: call {{.*}}@llvm.invariant.start.p0(i64 noundef 4, ptr @c)
 
 // CHECK: call noundef i32 @_Z1fv(
 // CHECK: store {{.*}}, ptr @d
 // CHECK: call {{.*}}@llvm.invariant.start.p0(i64 4, ptr @d)
 
 // CHECK-LABEL: define{{.*}} void @_Z1ev(
 // CHECK: call void @_ZN1AC1Ev(ptr noundef {{[^,]*}} @_ZZ1evE1a)
 // CHECK: call {{.*}}@llvm.invariant.start.p0(i64 4, ptr {{.*}}@_ZZ1evE1a)
 // CHECK-NOT: llvm.invariant.end

clang/test/CodeGenCXX/static-init.cpp

 // RUN: %clang_cc1 %s -triple=x86_64-pc-linuxs -emit-llvm -std=c++98 -o - | FileCheck -check-prefix=CHECK -check-prefix=CHECK98 %s
 // RUN: %clang_cc1 %s -triple=x86_64-pc-linuxs -emit-llvm -std=c++11 -o - | FileCheck -check-prefix=CHECK -check-prefix=CHECK11 %s
+// RUN: %clang_cc1 %s -triple=x86_64-pc-linuxs -emit-llvm -std=c++20 -o - | FileCheck -check-prefix=CHECK -check-prefix=CHECK20 %s
 
 // CHECK: @_ZZ1hvE1i = internal global i32 0, align 4
 // CHECK: @base_req ={{.*}} global [4 x i8] c"foo\00", align 1
 // CHECK: @base_req_uchar ={{.*}} global [4 x i8] c"bar\00", align 1
 
 // CHECK: @_ZZN5test31BC1EvE1u = internal global { i8, [3 x i8] } { i8 97, [3 x i8] undef }, align 4
 
+// CHECK20: @_ZZN5test51fEvE1a = internal constant %"struct.test5::A" { i32 42 }
+
 // CHECK: @_ZZ2h2vE1i = linkonce_odr global i32 0, comdat, align 4
 // CHECK: @_ZGVZ2h2vE1i = linkonce_odr global i64 0, comdat, align 8{{$}}
 // CHECK: @_ZZN5test1L6getvarEiE3var = internal constant [4 x i32] [i32 1, i32 0, i32 2, i32 4], align 16
 // CHECK98: @_ZZN5test414useStaticLocalEvE3obj = linkonce_odr global %"struct.test4::HasVTable" zeroinitializer, comdat, align 8
 // CHECK11: @_ZZN5test414useStaticLocalEvE3obj = linkonce_odr global %"struct.test4::HasVTable" { ptr getelementptr inbounds ({ [3 x ptr] }, ptr @_ZTVN5test49HasVTableE, i32 0, inrange i32 0, i32 2) }, comdat, align 8
 
 struct A {
   A();
inline HasVTable &useStaticLocal() {
   return obj;
 }
 void useit() {
   useStaticLocal();
 }
 // CHECK: define linkonce_odr noundef nonnull align 8 dereferenceable(8) ptr @_ZN5test414useStaticLocalEv()
 // CHECK: ret ptr{{.*}} @_ZZN5test414useStaticLocalEvE3obj
 }
+
+#if __cplusplus >= 202002L
+// A const object with constexpr destructor can be emitted as a constant.
+namespace test5 {
+  struct A {
+    constexpr A(int x) : x_(x) {}
+    constexpr ~A() {}
+    int x_;
+  };
+  const int *f() {
+    static const A a{42};
+    return &a.x_;
+  }
+}
+#endif