1 files changed, 194 insertions, 16 deletions

diff --git a/lib/CodeGen/CGCXX.cpp b/lib/CodeGen/CGCXX.cpp
index 28c4c6b..4889fc0 100644
--- a/lib/CodeGen/CGCXX.cpp
+++ b/lib/CodeGen/CGCXX.cpp
@@ -22,33 +22,182 @@
 #include "clang/AST/DeclCXX.h"
 #include "clang/AST/DeclObjC.h"
 #include "clang/AST/StmtCXX.h"
+#include "clang/CodeGen/CodeGenOptions.h"
 #include "llvm/ADT/StringExtras.h"
 using namespace clang;
 using namespace CodeGen;
 
+/// Determines whether the given function has a trivial body that does
+/// not require any specific codegen.
+static bool HasTrivialBody(const FunctionDecl *FD) {
+  Stmt *S = FD->getBody();
+  if (!S)
+    return true;
+  if (isa<CompoundStmt>(S) && cast<CompoundStmt>(S)->body_empty())
+    return true;
+  return false;
+}
+
+/// Try to emit a base destructor as an alias to its primary
+/// base-class destructor.
+bool CodeGenModule::TryEmitBaseDestructorAsAlias(const CXXDestructorDecl *D) {
+  if (!getCodeGenOpts().CXXCtorDtorAliases)
+    return true;
+
+  // If the destructor doesn't have a trivial body, we have to emit it
+  // separately.
+  if (!HasTrivialBody(D))
+    return true;
+
+  const CXXRecordDecl *Class = D->getParent();
+
+  // If we need to manipulate a VTT parameter, give up.
+  if (Class->getNumVBases()) {
+    // Extra Credit:  passing extra parameters is perfectly safe
+    // in many calling conventions, so only bail out if the ctor's
+    // calling convention is nonstandard.
+    return true;
+  }
+
+  // If any fields have a non-trivial destructor, we have to emit it
+  // separately.
+  for (CXXRecordDecl::field_iterator I = Class->field_begin(),
+         E = Class->field_end(); I != E; ++I)
+    if (const RecordType *RT = (*I)->getType()->getAs<RecordType>())
+      if (!cast<CXXRecordDecl>(RT->getDecl())->hasTrivialDestructor())
+        return true;
+
+  // Try to find a unique base class with a non-trivial destructor.
+  const CXXRecordDecl *UniqueBase = 0;
+  for (CXXRecordDecl::base_class_const_iterator I = Class->bases_begin(),
+         E = Class->bases_end(); I != E; ++I) {
+
+    // We're in the base destructor, so skip virtual bases.
+    if (I->isVirtual()) continue;
+
+    // Skip base classes with trivial destructors.
+    const CXXRecordDecl *Base
+      = cast<CXXRecordDecl>(I->getType()->getAs<RecordType>()->getDecl());
+    if (Base->hasTrivialDestructor()) continue;
+
+    // If we've already found a base class with a non-trivial
+    // destructor, give up.
+    if (UniqueBase) return true;
+    UniqueBase = Base;
+  }
+
+  // If we didn't find any bases with a non-trivial destructor, then
+  // the base destructor is actually effectively trivial, which can
+  // happen if it was needlessly user-defined or if there are virtual
+  // bases with non-trivial destructors.
+  if (!UniqueBase)
+    return true;
+
+  /// If we don't have a definition for the destructor yet, don't
+  /// emit.  We can't emit aliases to declarations; that's just not
+  /// how aliases work.
+  const CXXDestructorDecl *BaseD = UniqueBase->getDestructor(getContext());
+  if (!BaseD->isImplicit() && !BaseD->getBody())
+    return true;
+
+  // If the base is at a non-zero offset, give up.
+  const ASTRecordLayout &ClassLayout = Context.getASTRecordLayout(Class);
+  if (ClassLayout.getBaseClassOffset(UniqueBase) != 0)
+    return true;
+
+  return TryEmitDefinitionAsAlias(GlobalDecl(D, Dtor_Base),
+                                  GlobalDecl(BaseD, Dtor_Base));
+}
 
+/// Try to emit a definition as a global alias for another definition.
+bool CodeGenModule::TryEmitDefinitionAsAlias(GlobalDecl AliasDecl,
+                                             GlobalDecl TargetDecl) {
+  if (!getCodeGenOpts().CXXCtorDtorAliases)
+    return true;
+
+  // 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;
+  }
+
+  // Derive the type for the alias.
+  const llvm::PointerType *AliasType
+    = getTypes().GetFunctionType(AliasDecl)->getPointerTo();
+
+  // Find the referrent.  Some aliases might require a bitcast, in
+  // which case the caller is responsible for ensuring the soundness
+  // of these semantics.
+  llvm::GlobalValue *Ref = cast<llvm::GlobalValue>(GetAddrOfGlobal(TargetDecl));
+  llvm::Constant *Aliasee = Ref;
+  if (Ref->getType() != AliasType)
+    Aliasee = llvm::ConstantExpr::getBitCast(Ref, AliasType);
+
+  // Create the alias with no name.
+  llvm::GlobalAlias *Alias = 
+    new llvm::GlobalAlias(AliasType, Linkage, "", Aliasee, &getModule());
+
+  // Switch any previous uses to the alias.
+  const char *MangledName = getMangledName(AliasDecl);
+  llvm::GlobalValue *&Entry = GlobalDeclMap[MangledName];
+  if (Entry) {
+    assert(Entry->isDeclaration() && "definition already exists for alias");
+    assert(Entry->getType() == AliasType &&
+           "declaration exists with different type");
+    Entry->replaceAllUsesWith(Alias);
+    Entry->eraseFromParent();
+  }
+  Entry = Alias;
 
-llvm::Value *CodeGenFunction::LoadCXXThis() {
-  assert(isa<CXXMethodDecl>(CurFuncDecl) &&
-         "Must be in a C++ member function decl to load 'this'");
-  assert(cast<CXXMethodDecl>(CurFuncDecl)->isInstance() &&
-         "Must be in a C++ member function decl to load 'this'");
+  // Finally, set up the alias with its proper name and attributes.
+  Alias->setName(MangledName);
+  SetCommonAttributes(AliasDecl.getDecl(), Alias);
 
-  // FIXME: What if we're inside a block?
-  // ans: See how CodeGenFunction::LoadObjCSelf() uses
-  // CodeGenFunction::BlockForwardSelf() for how to do this.
-  return Builder.CreateLoad(LocalDeclMap[CXXThisDecl], "this");
+  return false;
 }
 
 void CodeGenModule::EmitCXXConstructors(const CXXConstructorDecl *D) {
+  // The constructor used for constructing this as a complete class;
+  // constucts the virtual bases, then calls the base constructor.
   EmitGlobal(GlobalDecl(D, Ctor_Complete));
+
+  // The constructor used for constructing this as a base class;
+  // ignores virtual bases.
   EmitGlobal(GlobalDecl(D, Ctor_Base));
 }
 
 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);
 
@@ -56,15 +205,17 @@ 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)));
 }
@@ -79,15 +230,39 @@ const char *CodeGenModule::getMangledCXXCtorName(const CXXConstructorDecl *D,
 }
 
 void CodeGenModule::EmitCXXDestructors(const CXXDestructorDecl *D) {
+  // 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));
+
+  // 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 used for destructing this as a base class; ignores
+  // virtual bases.
   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;
+
+  // The base destructor is equivalent to the base destructor of its
+  // base class if there is exactly one non-virtual base class with a
+  // non-trivial destructor, there are no fields with a non-trivial
+  // destructor, and the body of the destructor is trivial.
+  if (Type == Dtor_Base && !TryEmitBaseDestructorAsAlias(D))
+    return;
+
+  llvm::Function *Fn = cast<llvm::Function>(GetAddrOfCXXDestructor(D, Type));
 
   CodeGenFunction(*this).GenerateCode(GlobalDecl(D, Type), Fn);
 
@@ -95,13 +270,16 @@ 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)));
 }