lib/CodeGen/CGCXXClass.cpp

//===--- CGCXXClass.cpp - Emit LLVM Code for C++ classes ------------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This contains code dealing with C++ code generation of classes
//
//===----------------------------------------------------------------------===//

#include "CodeGenFunction.h"
#include "clang/AST/RecordLayout.h"
using namespace clang;
using namespace CodeGen;

static bool
GetNestedPaths(llvm::SmallVectorImpl<const CXXRecordDecl *> &NestedBasePaths,
               const CXXRecordDecl *ClassDecl,
               const CXXRecordDecl *BaseClassDecl) {
  for (CXXRecordDecl::base_class_const_iterator i = ClassDecl->bases_begin(),
      e = ClassDecl->bases_end(); i != e; ++i) {
    if (i->isVirtual())
      continue;
    const CXXRecordDecl *Base =
      cast<CXXRecordDecl>(i->getType()->getAs<RecordType>()->getDecl());
    if (Base == BaseClassDecl) {
      NestedBasePaths.push_back(BaseClassDecl);
      return true;
    }
  }
  // BaseClassDecl not an immediate base of ClassDecl.
  for (CXXRecordDecl::base_class_const_iterator i = ClassDecl->bases_begin(),
       e = ClassDecl->bases_end(); i != e; ++i) {
    if (i->isVirtual())
      continue;
    const CXXRecordDecl *Base =
      cast<CXXRecordDecl>(i->getType()->getAs<RecordType>()->getDecl());
    if (GetNestedPaths(NestedBasePaths, Base, BaseClassDecl)) {
      NestedBasePaths.push_back(Base);
      return true;
    }
  }
  return false;
}

static uint64_t ComputeBaseClassOffset(ASTContext &Context,
                                       const CXXRecordDecl *ClassDecl,
                                       const CXXRecordDecl *BaseClassDecl) {
    uint64_t Offset = 0;

    llvm::SmallVector<const CXXRecordDecl *, 16> NestedBasePaths;
    GetNestedPaths(NestedBasePaths, ClassDecl, BaseClassDecl);
    assert(NestedBasePaths.size() > 0 &&
           "AddressCXXOfBaseClass - inheritence path failed");
    NestedBasePaths.push_back(ClassDecl);
    
    for (unsigned i = NestedBasePaths.size() - 1; i > 0; i--) {
        const CXXRecordDecl *DerivedClass = NestedBasePaths[i];
        const CXXRecordDecl *BaseClass = NestedBasePaths[i-1];
        const ASTRecordLayout &Layout = 
            Context.getASTRecordLayout(DerivedClass);
        
        Offset += Layout.getBaseClassOffset(BaseClass) / 8;
    }
    
    return Offset;
}

llvm::Constant *
CodeGenModule::GetCXXBaseClassOffset(const CXXRecordDecl *ClassDecl,
                                     const CXXRecordDecl *BaseClassDecl) {
  if (ClassDecl == BaseClassDecl)
    return 0;

  QualType BTy =
    getContext().getCanonicalType(
      getContext().getTypeDeclType(const_cast<CXXRecordDecl*>(BaseClassDecl)));

  uint64_t Offset = ComputeBaseClassOffset(getContext(), 
                                           ClassDecl, BaseClassDecl);
  if (!Offset)
    return 0;

  const llvm::Type *PtrDiffTy = 
    Types.ConvertType(getContext().getPointerDiffType());

  return llvm::ConstantInt::get(PtrDiffTy, Offset);
}

llvm::Value *
CodeGenFunction::GetAddressCXXOfBaseClass(llvm::Value *BaseValue,
                                          const CXXRecordDecl *ClassDecl,
                                          const CXXRecordDecl *BaseClassDecl,
                                          bool NullCheckValue) {
  llvm::Constant *Offset = CGM.GetCXXBaseClassOffset(ClassDecl, BaseClassDecl);
  
  QualType BTy =
    getContext().getCanonicalType(
      getContext().getTypeDeclType(const_cast<CXXRecordDecl*>(BaseClassDecl)));
  const llvm::Type *BasePtrTy = llvm::PointerType::getUnqual(ConvertType(BTy));

  if (!Offset) {
    // Just cast back.
    return Builder.CreateBitCast(BaseValue, BasePtrTy);
  }
  
  llvm::BasicBlock *CastNull = 0;
  llvm::BasicBlock *CastNotNull = 0;
  llvm::BasicBlock *CastEnd = 0;
  
  if (NullCheckValue) {
    CastNull = createBasicBlock("cast.null");
    CastNotNull = createBasicBlock("cast.notnull");
    CastEnd = createBasicBlock("cast.end");
    
    llvm::Value *IsNull = 
      Builder.CreateICmpEQ(BaseValue,
                           llvm::Constant::getNullValue(BaseValue->getType()));
    Builder.CreateCondBr(IsNull, CastNull, CastNotNull);
    EmitBlock(CastNotNull);
  }
  
  const llvm::Type *Int8PtrTy = 
    llvm::PointerType::getUnqual(llvm::Type::getInt8Ty(VMContext));
  
  // Apply the offset.
  BaseValue = Builder.CreateBitCast(BaseValue, Int8PtrTy);
  BaseValue = Builder.CreateGEP(BaseValue, Offset, "add.ptr");
  
  // Cast back.
  BaseValue = Builder.CreateBitCast(BaseValue, BasePtrTy);
 
  if (NullCheckValue) {
    Builder.CreateBr(CastEnd);
    EmitBlock(CastNull);
    Builder.CreateBr(CastEnd);
    EmitBlock(CastEnd);
    
    llvm::PHINode *PHI = Builder.CreatePHI(BaseValue->getType());
    PHI->reserveOperandSpace(2);
    PHI->addIncoming(BaseValue, CastNotNull);
    PHI->addIncoming(llvm::Constant::getNullValue(BaseValue->getType()), 
                     CastNull);
    BaseValue = PHI;
  }
  
  return BaseValue;
}