Patch from David Chisnall:

The attached diff fixes the //FIXME in message send to super.  This
should now be faster, and works in the presence of class posing.  This
is now the same approach as used in GCC (the earlier code was a quick
hack to get something working).


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@70868 91177308-0d34-0410-b5e6-96231b3b80d8

lib/CodeGen/CGObjCGNU.cpp

@@ -52,6 +52,8 @@ private:
   const llvm::PointerType *PtrTy;
   const llvm::IntegerType *LongTy;
   const llvm::PointerType *PtrToIntTy;
+  llvm::GlobalAlias *ClassPtrAlias;
+  llvm::GlobalAlias *MetaClassPtrAlias;
   std::vector<llvm::Constant*> Classes;
   std::vector<llvm::Constant*> Categories;
   std::vector<llvm::Constant*> ConstantStrings;
@@ -169,7 +171,8 @@ static std::string SymbolNameForMethod(const std::string &ClassName, const
 }
 
 CGObjCGNU::CGObjCGNU(CodeGen::CodeGenModule &cgm)
-  : CGM(cgm), TheModule(CGM.getModule()) {
+  : CGM(cgm), TheModule(CGM.getModule()), ClassPtrAlias(0),
+    MetaClassPtrAlias(0) {
   IntTy = cast<llvm::IntegerType>(
       CGM.getTypes().ConvertType(CGM.getContext().IntTy));
   LongTy = cast<llvm::IntegerType>(
@@ -297,23 +300,42 @@ CGObjCGNU::GenerateMessageSendSuper(CodeGen::CodeGenFunction &CGF,
   const llvm::FunctionType *impType = Types.GetFunctionType(FnInfo, false);
 
 
-  const ObjCInterfaceDecl *SuperClass = Class->getSuperClass();
-  // TODO: This should be cached, not looked up every time.
-  llvm::Value *ReceiverClass = GetClass(CGF.Builder, SuperClass);
-  if (IsClassMessage)
-  {
-    ReceiverClass = CGF.Builder.CreateBitCast(ReceiverClass, 
-      llvm::PointerType::getUnqual(IdTy));
-    ReceiverClass = CGF.Builder.CreateBitCast(CGF.Builder.CreateLoad(
-      ReceiverClass), IdTy);
+  // Set up global aliases for the metaclass or class pointer if they do not
+  // already exist.  These will are forward-references which will be set to
+  // pointers to the class and metaclass structure created for the runtime load
+  // function.  To send a message to super, we look up the value of the
+  // super_class pointer from either the class or metaclass structure.
+  llvm::Value *ReceiverClass = 0;
+  if (IsClassMessage)  {
+    if (!MetaClassPtrAlias) {
+      MetaClassPtrAlias = new llvm::GlobalAlias(IdTy,
+          llvm::GlobalValue::InternalLinkage, ".objc_metaclass_ref" + Class->getNameAsString(), NULL,
+          &TheModule);
+    }
+    ReceiverClass = MetaClassPtrAlias;
+  } else {
+    if (!ClassPtrAlias) {
+      ClassPtrAlias = new llvm::GlobalAlias(IdTy,
+          llvm::GlobalValue::InternalLinkage, ".objc_class_ref" + Class->getNameAsString(), NULL,
+          &TheModule);
+    }
+    ReceiverClass = ClassPtrAlias;
   }
+  // Cast the pointer to a simplified version of the class structure
+  ReceiverClass = CGF.Builder.CreateBitCast(ReceiverClass, 
+      llvm::PointerType::getUnqual(llvm::StructType::get(IdTy, IdTy, NULL)));
+  // Get the superclass pointer
+  ReceiverClass = CGF.Builder.CreateStructGEP(ReceiverClass, 1);
+  // Load the superclass pointer
+  ReceiverClass = CGF.Builder.CreateLoad(ReceiverClass);
   // Construct the structure used to look up the IMP
   llvm::StructType *ObjCSuperTy = llvm::StructType::get(Receiver->getType(),
       IdTy, NULL);
   llvm::Value *ObjCSuper = CGF.Builder.CreateAlloca(ObjCSuperTy);
 
   CGF.Builder.CreateStore(Receiver, CGF.Builder.CreateStructGEP(ObjCSuper, 0));
-  CGF.Builder.CreateStore(ReceiverClass, CGF.Builder.CreateStructGEP(ObjCSuper, 1));
+  CGF.Builder.CreateStore(ReceiverClass,
+      CGF.Builder.CreateStructGEP(ObjCSuper, 1));
 
   // Get the IMP
   std::vector<const llvm::Type*> Params;
@@ -819,12 +841,26 @@ void CGObjCGNU::GenerateClass(const ObjCImplementationDecl *OID) {
   llvm::Constant *MetaClassStruct = GenerateClassStructure(NULLPtr,
       NULLPtr, 0x2L, /*name*/"", 0, Zeros[0], GenerateIvarList(
         empty, empty, empty), ClassMethodList, NULLPtr);
+
   // Generate the class structure
   llvm::Constant *ClassStruct =
     GenerateClassStructure(MetaClassStruct, SuperClass, 0x1L,
                            ClassName.c_str(), 0,
       llvm::ConstantInt::get(LongTy, instanceSize), IvarList,
       MethodList, GenerateProtocolList(Protocols));
+
+  // Resolve the class aliases, if they exist.
+  if (ClassPtrAlias) {
+    ClassPtrAlias->setAliasee(
+        llvm::ConstantExpr::getBitCast(ClassStruct, IdTy));
+    ClassPtrAlias = 0;
+  }
+  if (MetaClassPtrAlias) {
+    MetaClassPtrAlias->setAliasee(
+        llvm::ConstantExpr::getBitCast(MetaClassStruct, IdTy));
+    MetaClassPtrAlias = 0;
+  }
+
   // Add class structure to list to be added to the symtab later
   ClassStruct = llvm::ConstantExpr::getBitCast(ClassStruct, PtrToInt8Ty);
   Classes.push_back(ClassStruct);