Emit complete constructors and destructors as aliases to base constructors

and destructors when the two entities are semantically identical, i.e. when
the class has no virtual base classes.  We only do this for linkage types
for which aliases are supported, i.e. internal and external, i.e. not linkonce.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@96451 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/CodeGen/CGCXX.cpp b/lib/CodeGen/CGCXX.cpp
index c4c52aac034af3e39b04517cc83fbf25dac2847e..f0d01969a9cebbab44622a626821a64a1a86cf72 100644 (file)
--- a/lib/CodeGen/CGCXX.cpp
+++ b/lib/CodeGen/CGCXX.cpp
@@ -26,17 +26,88 @@
 using namespace clang;
 using namespace CodeGen;
 
+/// Try to emit a definition as a global alias for another definition.
+bool CodeGenModule::TryEmitDefinitionAsAlias(GlobalDecl AliasDecl,
+                                             GlobalDecl TargetDecl) {
+  // Find the referrent.
+  llvm::GlobalValue *Ref = cast<llvm::GlobalValue>(GetAddrOfGlobal(TargetDecl));
+
+  // Look for an existing entry.
+  const char *MangledName = getMangledName(AliasDecl);
+  llvm::GlobalValue *&Entry = GlobalDeclMap[MangledName];
+  if (Entry) {
+    assert(Entry->isDeclaration() && "definition already exists for alias");
+    assert(Entry->getType() == Ref->getType() &&
+           "declaration exists with different type");
+  }
+
+  // The alias will use the linkage of the referrent.  If we can't
+  // support aliases with that linkage, fail.
+  llvm::GlobalValue::LinkageTypes Linkage
+    = getFunctionLinkage(cast<FunctionDecl>(AliasDecl.getDecl()));
+
+  switch (Linkage) {
+  // We can definitely emit aliases to definitions with external linkage.
+  case llvm::GlobalValue::ExternalLinkage:
+  case llvm::GlobalValue::ExternalWeakLinkage:
+    break;
+
+  // Same with local linkage.
+  case llvm::GlobalValue::InternalLinkage:
+  case llvm::GlobalValue::PrivateLinkage:
+  case llvm::GlobalValue::LinkerPrivateLinkage:
+    break;
+
+  // We should try to support linkonce linkages.
+  case llvm::GlobalValue::LinkOnceAnyLinkage:
+  case llvm::GlobalValue::LinkOnceODRLinkage:
+    return true;
+
+  // Other linkages will probably never be supported.
+  default:
+    return true;
+  }
+
+  // Create the alias with no name.
+  llvm::GlobalAlias *Alias = 
+    new llvm::GlobalAlias(Ref->getType(), Linkage, "", Ref, &getModule());
+
+  // Switch any previous uses to the alias and continue.
+  if (Entry) {
+    Entry->replaceAllUsesWith(Alias);
+    Entry->eraseFromParent();
+  }
+  Entry = Alias;
+
+  // Finally, set up the alias with its proper name and attributes.
+  Alias->setName(MangledName);
+  SetCommonAttributes(AliasDecl.getDecl(), Alias);
+
+  return false;
+}
 
 
 void CodeGenModule::EmitCXXConstructors(const CXXConstructorDecl *D) {
-  EmitGlobal(GlobalDecl(D, Ctor_Complete));
+  // The constructor used for constructing this as a base class;
+  // ignores virtual bases.
   EmitGlobal(GlobalDecl(D, Ctor_Base));
+
+  // The constructor used for constructing this as a complete class;
+  // constucts the virtual bases, then calls the base constructor.
+  EmitGlobal(GlobalDecl(D, Ctor_Complete));
 }
 
 void CodeGenModule::EmitCXXConstructor(const CXXConstructorDecl *D,
                                        CXXCtorType Type) {
+  // The complete constructor is equivalent to the base constructor
+  // for classes with no virtual bases.  Try to emit it as an alias.
+  if (Type == Ctor_Complete &&
+      !D->getParent()->getNumVBases() &&
+      !TryEmitDefinitionAsAlias(GlobalDecl(D, Ctor_Complete),
+                                GlobalDecl(D, Ctor_Base)))
+    return;
 
-  llvm::Function *Fn = GetAddrOfCXXConstructor(D, Type);
+  llvm::Function *Fn = cast<llvm::Function>(GetAddrOfCXXConstructor(D, Type));
 
   CodeGenFunction(*this).GenerateCode(GlobalDecl(D, Type), Fn);
 
@@ -44,15 +115,17 @@ void CodeGenModule::EmitCXXConstructor(const CXXConstructorDecl *D,
   SetLLVMFunctionAttributesForDefinition(D, Fn);
 }
 
-llvm::Function *
+llvm::GlobalValue *
 CodeGenModule::GetAddrOfCXXConstructor(const CXXConstructorDecl *D,
                                        CXXCtorType Type) {
+  const char *Name = getMangledCXXCtorName(D, Type);
+  if (llvm::GlobalValue *V = GlobalDeclMap[Name])
+    return V;
+
   const FunctionProtoType *FPT = D->getType()->getAs<FunctionProtoType>();
   const llvm::FunctionType *FTy =
     getTypes().GetFunctionType(getTypes().getFunctionInfo(D, Type), 
                                FPT->isVariadic());
-
-  const char *Name = getMangledCXXCtorName(D, Type);
   return cast<llvm::Function>(
                       GetOrCreateLLVMFunction(Name, FTy, GlobalDecl(D, Type)));
 }
@@ -67,15 +140,32 @@ const char *CodeGenModule::getMangledCXXCtorName(const CXXConstructorDecl *D,
 }
 
 void CodeGenModule::EmitCXXDestructors(const CXXDestructorDecl *D) {
+  // The destructor used for destructing this as a base class; ignores
+  // virtual bases.
+  EmitGlobal(GlobalDecl(D, Dtor_Base));
+
+  // The destructor used for destructing this as a most-derived class;
+  // call the base destructor and then destructs any virtual bases.
+  EmitGlobal(GlobalDecl(D, Dtor_Complete));
+
+  // The destructor in a virtual table is always a 'deleting'
+  // destructor, which calls the complete destructor and then uses the
+  // appropriate operator delete.
   if (D->isVirtual())
     EmitGlobal(GlobalDecl(D, Dtor_Deleting));
-  EmitGlobal(GlobalDecl(D, Dtor_Complete));
-  EmitGlobal(GlobalDecl(D, Dtor_Base));
 }
 
 void CodeGenModule::EmitCXXDestructor(const CXXDestructorDecl *D,
                                       CXXDtorType Type) {
-  llvm::Function *Fn = GetAddrOfCXXDestructor(D, Type);
+  // The complete destructor is equivalent to the base destructor for
+  // classes with no virtual bases, so try to emit it as an alias.
+  if (Type == Dtor_Complete &&
+      !D->getParent()->getNumVBases() &&
+      !TryEmitDefinitionAsAlias(GlobalDecl(D, Dtor_Complete),
+                                GlobalDecl(D, Dtor_Base)))
+    return;
+
+  llvm::Function *Fn = cast<llvm::Function>(GetAddrOfCXXDestructor(D, Type));
 
   CodeGenFunction(*this).GenerateCode(GlobalDecl(D, Type), Fn);
 
@@ -83,13 +173,16 @@ void CodeGenModule::EmitCXXDestructor(const CXXDestructorDecl *D,
   SetLLVMFunctionAttributesForDefinition(D, Fn);
 }
 
-llvm::Function *
+llvm::GlobalValue *
 CodeGenModule::GetAddrOfCXXDestructor(const CXXDestructorDecl *D,
                                       CXXDtorType Type) {
+  const char *Name = getMangledCXXDtorName(D, Type);
+  if (llvm::GlobalValue *V = GlobalDeclMap[Name])
+    return V;
+
   const llvm::FunctionType *FTy =
     getTypes().GetFunctionType(getTypes().getFunctionInfo(D, Type), false);
 
-  const char *Name = getMangledCXXDtorName(D, Type);
   return cast<llvm::Function>(
                       GetOrCreateLLVMFunction(Name, FTy, GlobalDecl(D, Type)));
 }

diff --git a/lib/CodeGen/CodeGenModule.cpp b/lib/CodeGen/CodeGenModule.cpp
index 5a552c490ac65799025a68da16c995a0a7d377a1..41575e41e53cdb135b6104edef50b9ddf99c7c21 100644 (file)
--- a/lib/CodeGen/CodeGenModule.cpp
+++ b/lib/CodeGen/CodeGenModule.cpp
@@ -316,24 +316,20 @@ GetLinkageForFunction(ASTContext &Context, const FunctionDecl *FD,
   return CodeGenModule::GVA_CXXInline;
 }
 
-/// SetFunctionDefinitionAttributes - Set attributes for a global.
-///
-/// FIXME: This is currently only done for aliases and functions, but not for
-/// variables (these details are set in EmitGlobalVarDefinition for variables).
-void CodeGenModule::SetFunctionDefinitionAttributes(const FunctionDecl *D,
-                                                    llvm::GlobalValue *GV) {
+llvm::GlobalValue::LinkageTypes
+CodeGenModule::getFunctionLinkage(const FunctionDecl *D) {
   GVALinkage Linkage = GetLinkageForFunction(getContext(), D, Features);
 
   if (Linkage == GVA_Internal) {
-    GV->setLinkage(llvm::Function::InternalLinkage);
+    return llvm::Function::InternalLinkage;
   } else if (D->hasAttr<DLLExportAttr>()) {
-    GV->setLinkage(llvm::Function::DLLExportLinkage);
+    return llvm::Function::DLLExportLinkage;
   } else if (D->hasAttr<WeakAttr>()) {
-    GV->setLinkage(llvm::Function::WeakAnyLinkage);
+    return llvm::Function::WeakAnyLinkage;
   } else if (Linkage == GVA_C99Inline) {
     // In C99 mode, 'inline' functions are guaranteed to have a strong
     // definition somewhere else, so we can use available_externally linkage.
-    GV->setLinkage(llvm::Function::AvailableExternallyLinkage);
+    return llvm::Function::AvailableExternallyLinkage;
   } else if (Linkage == GVA_CXXInline || Linkage == GVA_TemplateInstantiation) {
     // In C++, the compiler has to emit a definition in every translation unit
     // that references the function.  We should use linkonce_odr because
@@ -341,13 +337,22 @@ void CodeGenModule::SetFunctionDefinitionAttributes(const FunctionDecl *D,
     // don't need to codegen it.  b) if the function persists, it needs to be
     // merged with other definitions. c) C++ has the ODR, so we know the
     // definition is dependable.
-    GV->setLinkage(llvm::Function::LinkOnceODRLinkage);
+    return llvm::Function::LinkOnceODRLinkage;
   } else {
     assert(Linkage == GVA_StrongExternal);
     // Otherwise, we have strong external linkage.
-    GV->setLinkage(llvm::Function::ExternalLinkage);
+    return llvm::Function::ExternalLinkage;
   }
+}
+
 
+/// SetFunctionDefinitionAttributes - Set attributes for a global.
+///
+/// FIXME: This is currently only done for aliases and functions, but not for
+/// variables (these details are set in EmitGlobalVarDefinition for variables).
+void CodeGenModule::SetFunctionDefinitionAttributes(const FunctionDecl *D,
+                                                    llvm::GlobalValue *GV) {
+  GV->setLinkage(getFunctionLinkage(D));
   SetCommonAttributes(D, GV);
 }
 

diff --git a/lib/CodeGen/CodeGenModule.h b/lib/CodeGen/CodeGenModule.h
index 8280766c7035366750380e095fb124b80da2623a..a5e1d9f12b33e71823bbfeb784958cb521cfd199 100644 (file)
--- a/lib/CodeGen/CodeGenModule.h
+++ b/lib/CodeGen/CodeGenModule.h
@@ -206,6 +206,19 @@ public:
   /// GlobalValue.
   void setGlobalVisibility(llvm::GlobalValue *GV, const Decl *D) const;
 
+  llvm::Constant *GetAddrOfGlobal(GlobalDecl GD) {
+    if (isa<CXXConstructorDecl>(GD.getDecl()))
+      return GetAddrOfCXXConstructor(cast<CXXConstructorDecl>(GD.getDecl()),
+                                     GD.getCtorType());
+    else if (isa<CXXDestructorDecl>(GD.getDecl()))
+      return GetAddrOfCXXDestructor(cast<CXXDestructorDecl>(GD.getDecl()),
+                                     GD.getDtorType());
+    else if (isa<FunctionDecl>(GD.getDecl()))
+      return GetAddrOfFunction(GD);
+    else
+      return GetAddrOfGlobalVar(cast<VarDecl>(GD.getDecl()));
+  }
+
   /// GetAddrOfGlobalVar - Return the llvm::Constant for the address of the
   /// given global variable.  If Ty is non-null and if the global doesn't exist,
   /// then it will be greated with the specified type instead of whatever the
@@ -291,13 +304,13 @@ public:
 
   /// GetAddrOfCXXConstructor - Return the address of the constructor of the
   /// given type.
-  llvm::Function *GetAddrOfCXXConstructor(const CXXConstructorDecl *D,
-                                          CXXCtorType Type);
+  llvm::GlobalValue *GetAddrOfCXXConstructor(const CXXConstructorDecl *D,
+                                             CXXCtorType Type);
 
   /// GetAddrOfCXXDestructor - Return the address of the constructor of the
   /// given type.
-  llvm::Function *GetAddrOfCXXDestructor(const CXXDestructorDecl *D,
-                                         CXXDtorType Type);
+  llvm::GlobalValue *GetAddrOfCXXDestructor(const CXXDestructorDecl *D,
+                                            CXXDtorType Type);
 
   /// getBuiltinLibFunction - Given a builtin id for a function like
   /// "__builtin_fabsf", return a Function* for "fabsf".
@@ -417,6 +430,9 @@ public:
     GVA_TemplateInstantiation
   };
 
+  llvm::GlobalVariable::LinkageTypes
+  getFunctionLinkage(const FunctionDecl *FD);
+
   /// getVtableLinkage - Return the appropriate linkage for the vtable, VTT,
   /// and type information of the given class.
   static llvm::GlobalVariable::LinkageTypes 
@@ -468,6 +484,8 @@ private:
 
   // C++ related functions.
 
+  bool TryEmitDefinitionAsAlias(GlobalDecl Alias, GlobalDecl Target);
+
   void EmitNamespace(const NamespaceDecl *D);
   void EmitLinkageSpec(const LinkageSpecDecl *D);
 

diff --git a/test/CodeGenCXX/default-arguments.cpp b/test/CodeGenCXX/default-arguments.cpp
index 282e5d0d5042248f7dad5ab4b1a6c39986d5c6e4..de53a6958f2b86fa56f41133471d256afb71c6c2 100644 (file)
--- a/test/CodeGenCXX/default-arguments.cpp
+++ b/test/CodeGenCXX/default-arguments.cpp
@@ -26,6 +26,8 @@ struct B {
  B(const A1& = A1(), const A2& = A2());
 };
 
+// CHECK: @_ZN1CC1Ev = alias {{.*}} @_ZN1CC2Ev
+
 // CHECK: define void @_Z2f1v()
 void f1() {
 
@@ -42,13 +44,6 @@ struct C {
  C();
 };
 
-// CHECK: define void @_ZN1CC1Ev(
-// CHECK: call void @_ZN2A1C1Ev(
-// CHECK: call void @_ZN2A2C1Ev(
-// CHECK: call void @_ZN1BC1ERK2A1RK2A2(
-// CHECK: call void @_ZN2A2D1Ev
-// CHECK: call void @_ZN2A1D1Ev
-
 // CHECK: define void @_ZN1CC2Ev(
 // CHECK: call void @_ZN2A1C1Ev(
 // CHECK: call void @_ZN2A2C1Ev(

diff --git a/test/CodeGenCXX/mangle-subst-std.cpp b/test/CodeGenCXX/mangle-subst-std.cpp
index 913c8f101b54d13dd922596e41393f1ead587d26..aea841557c98c7d11435d7e797002a97c4ebf9ed 100644 (file)
--- a/test/CodeGenCXX/mangle-subst-std.cpp
+++ b/test/CodeGenCXX/mangle-subst-std.cpp
@@ -1,9 +1,10 @@
 // RUN: %clang_cc1 -emit-llvm %s -o - -triple=x86_64-apple-darwin9 | FileCheck %s
 
+// CHECK: @_ZNSt1AC1Ev = alias {{.*}} @_ZNSt1AC2Ev
+
 namespace std {
   struct A { A(); };
   
-  // CHECK: define void @_ZNSt1AC1Ev
   // CHECK: define void @_ZNSt1AC2Ev
   A::A() { }
 };

diff --git a/test/CodeGenCXX/mangle.cpp b/test/CodeGenCXX/mangle.cpp
index 07183782e75e6b81196b1d76a8501315174e6e84..320b681ac87b26b63be83c549ed16e6675103642 100644 (file)
--- a/test/CodeGenCXX/mangle.cpp
+++ b/test/CodeGenCXX/mangle.cpp
@@ -11,6 +11,8 @@ struct Y { };
 //CHECK: @pr5966_i = external global
 //CHECK: @_ZL8pr5966_i = internal global
 
+// CHECK: @_ZN2S7C1Ev = alias {{.*}} @_ZN2S7C2Ev
+
 // CHECK: define zeroext i1 @_ZplRK1YRA100_P1X
 bool operator+(const Y&, X* (&xs)[100]) { return false; }
 
@@ -219,7 +221,6 @@ struct S7 {
 };
 
 // PR5139
-// CHECK: @_ZN2S7C1Ev
 // CHECK: @_ZN2S7C2Ev
 // CHECK: @"_ZN2S73$_0C1Ev"
 S7::S7() {}

diff --git a/test/CodeGenCXX/member-templates.cpp b/test/CodeGenCXX/member-templates.cpp
index 355ba20e171f6959a91d280a3e82587ecd18999f..5ec322629684327f842e4e8b6feea332ae63785f 100644 (file)
--- a/test/CodeGenCXX/member-templates.cpp
+++ b/test/CodeGenCXX/member-templates.cpp
@@ -15,7 +15,7 @@ struct B {
 
 template<typename T> B::B(T) {}
 
-// CHECK: define void @_ZN1BC1IiEET_(%struct.B* %this, i32)
+// CHECK: @_ZN1BC1IiEET_ = alias {{.*}} @_ZN1BC2IiEET_
 // CHECK: define void @_ZN1BC2IiEET_(%struct.B* %this, i32)
 template B::B(int);
 

diff --git a/test/CodeGenCXX/virtual-bases.cpp b/test/CodeGenCXX/virtual-bases.cpp
index 200f21a5da726e23f7c0d3d553be4a092418e2a2..bd29b8d9d381bee6f6d759a6168a90d0a89fbb32 100644 (file)
--- a/test/CodeGenCXX/virtual-bases.cpp
+++ b/test/CodeGenCXX/virtual-bases.cpp
@@ -4,7 +4,7 @@ struct A {
   A();
 };
 
-// CHECK: define void @_ZN1AC1Ev(%struct.A* %this)
+// CHECK: @_ZN1AC1Ev = alias {{.*}} @_ZN1AC2Ev
 // CHECK: define void @_ZN1AC2Ev(%struct.A* %this)
 A::A() { }
 
@@ -12,14 +12,14 @@ struct B : virtual A {
   B();
 };
 
-// CHECK: define void @_ZN1BC1Ev(%struct.B* %this)
 // CHECK: define void @_ZN1BC2Ev(%struct.B* %this, i8** %vtt)
+// CHECK: define void @_ZN1BC1Ev(%struct.B* %this)
 B::B() { }
 
 struct C : virtual A {
   C(bool);
 };
 
-// CHECK: define void @_ZN1CC1Eb(%struct.B* %this, i1 zeroext)
 // CHECK: define void @_ZN1CC2Eb(%struct.B* %this, i8** %vtt, i1 zeroext)
+// CHECK: define void @_ZN1CC1Eb(%struct.B* %this, i1 zeroext)
 C::C(bool) { }

diff --git a/test/CodeGenCXX/virtual-destructor-calls.cpp b/test/CodeGenCXX/virtual-destructor-calls.cpp
index 01ca1442f2c4cc52f421778962be529a4b6dc40c..650fd69bbe7d5f6cb3c7facd498953759e1f2acf 100644 (file)
--- a/test/CodeGenCXX/virtual-destructor-calls.cpp
+++ b/test/CodeGenCXX/virtual-destructor-calls.cpp
@@ -9,8 +9,7 @@ struct B : A {
 };
 
 // Complete dtor.
-// CHECK: define void @_ZN1BD1Ev
-// CHECK: call void @_ZN1AD2Ev
+// CHECK: @_ZN1BD1Ev = alias {{.*}} @_ZN1BD2Ev
 
 // Deleting dtor.
 // CHECK: define void @_ZN1BD0Ev

diff --git a/test/CodeGenCXX/vtable-pointer-initialization.cpp b/test/CodeGenCXX/vtable-pointer-initialization.cpp
index 92e011752f3fc1e4b412d25bcabe4ca08626f0dc..ebe531529b81aa8ac45dfdbcd46f46bc0c29d277 100644 (file)
--- a/test/CodeGenCXX/vtable-pointer-initialization.cpp
+++ b/test/CodeGenCXX/vtable-pointer-initialization.cpp
@@ -19,14 +19,14 @@ struct A : Base {
   Field field;
 };
 
-// CHECK: define void @_ZN1AC1Ev(
+// CHECK: define void @_ZN1AC2Ev(
 // CHECK: call void @_ZN4BaseC2Ev(
 // CHECK: store i8** getelementptr inbounds ([3 x i8*]* @_ZTV1A, i64 0, i64 2)
 // CHECK: call void @_ZN5FieldC1Ev(
 // CHECK: ret void
 A::A() { }
 
-// CHECK: define void @_ZN1AD1Ev(
+// CHECK: define void @_ZN1AD2Ev(
 // CHECK: store i8** getelementptr inbounds ([3 x i8*]* @_ZTV1A, i64 0, i64 2)
 // CHECK: call void @_ZN5FieldD1Ev(
 // CHECK: call void @_ZN4BaseD2Ev(