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//===------- ItaniumCXXABI.cpp - Emit LLVM Code from ASTs for a Module ----===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This provides C++ code generation targetting the Itanium C++ ABI. The class
// in this file generates structures that follow the Itanium C++ ABI, which is
// documented at:
// http://www.codesourcery.com/public/cxx-abi/abi.html
// http://www.codesourcery.com/public/cxx-abi/abi-eh.html
//
// It also supports the closely-related ARM ABI, documented at:
// http://infocenter.arm.com/help/topic/com.arm.doc.ihi0041c/IHI0041C_cppabi.pdf
//
//===----------------------------------------------------------------------===//
#include "CGCXXABI.h"
#include "CodeGenFunction.h"
#include "CodeGenModule.h"
#include "Mangle.h"
#include <clang/AST/Type.h>
#include <llvm/Value.h>
using namespace clang;
using namespace CodeGen;
namespace {
class ItaniumCXXABI : public CodeGen::CGCXXABI {
protected:
CodeGenModule &CGM;
CodeGen::MangleContext MangleCtx;
bool IsARM;
public:
ItaniumCXXABI(CodeGen::CodeGenModule &CGM, bool IsARM = false) :
CGM(CGM), MangleCtx(CGM.getContext(), CGM.getDiags()), IsARM(IsARM) { }
CodeGen::MangleContext &getMangleContext() {
return MangleCtx;
}
llvm::Value *EmitLoadOfMemberFunctionPointer(CodeGenFunction &CGF,
llvm::Value *&This,
llvm::Value *MemFnPtr,
const MemberPointerType *MPT);
void EmitMemberPointerConversion(CodeGenFunction &CGF,
const CastExpr *E,
llvm::Value *Src,
llvm::Value *Dest,
bool VolatileDest);
};
class ARMCXXABI : public ItaniumCXXABI {
public:
ARMCXXABI(CodeGen::CodeGenModule &CGM) : ItaniumCXXABI(CGM, /*ARM*/ true) {}
};
}
CodeGen::CGCXXABI *CodeGen::CreateItaniumCXXABI(CodeGenModule &CGM) {
return new ItaniumCXXABI(CGM);
}
CodeGen::CGCXXABI *CodeGen::CreateARMCXXABI(CodeGenModule &CGM) {
return new ARMCXXABI(CGM);
}
/// In the Itanium and ARM ABIs, method pointers have the form:
/// struct { ptrdiff_t ptr; ptrdiff_t adj; } memptr;
///
/// In the Itanium ABI:
/// - method pointers are virtual if (memptr.ptr & 1) is nonzero
/// - the this-adjustment is (memptr.adj)
/// - the virtual offset is (memptr.ptr - 1)
///
/// In the ARM ABI:
/// - method pointers are virtual if (memptr.adj & 1) is nonzero
/// - the this-adjustment is (memptr.adj >> 1)
/// - the virtual offset is (memptr.ptr)
/// ARM uses 'adj' for the virtual flag because Thumb functions
/// may be only single-byte aligned.
///
/// If the member is virtual, the adjusted 'this' pointer points
/// to a vtable pointer from which the virtual offset is applied.
///
/// If the member is non-virtual, memptr.ptr is the address of
/// the function to call.
llvm::Value *
ItaniumCXXABI::EmitLoadOfMemberFunctionPointer(CodeGenFunction &CGF,
llvm::Value *&This,
llvm::Value *MemFnPtr,
const MemberPointerType *MPT) {
CGBuilderTy &Builder = CGF.Builder;
const FunctionProtoType *FPT =
MPT->getPointeeType()->getAs<FunctionProtoType>();
const CXXRecordDecl *RD =
cast<CXXRecordDecl>(MPT->getClass()->getAs<RecordType>()->getDecl());
const llvm::FunctionType *FTy =
CGM.getTypes().GetFunctionType(CGM.getTypes().getFunctionInfo(RD, FPT),
FPT->isVariadic());
const llvm::IntegerType *ptrdiff = CGF.IntPtrTy;
llvm::Constant *ptrdiff_1 = llvm::ConstantInt::get(ptrdiff, 1);
llvm::BasicBlock *FnVirtual = CGF.createBasicBlock("memptr.virtual");
llvm::BasicBlock *FnNonVirtual = CGF.createBasicBlock("memptr.nonvirtual");
llvm::BasicBlock *FnEnd = CGF.createBasicBlock("memptr.end");
// Load memptr.adj, which is in the second field.
llvm::Value *RawAdj = Builder.CreateStructGEP(MemFnPtr, 1);
RawAdj = Builder.CreateLoad(RawAdj, "memptr.adj");
// Compute the true adjustment.
llvm::Value *Adj = RawAdj;
if (IsARM)
Adj = Builder.CreateAShr(Adj, ptrdiff_1, "memptr.adj.shifted");
// Apply the adjustment and cast back to the original struct type
// for consistency.
llvm::Value *Ptr = Builder.CreateBitCast(This, Builder.getInt8PtrTy());
Ptr = Builder.CreateInBoundsGEP(Ptr, Adj);
This = Builder.CreateBitCast(Ptr, This->getType(), "this.adjusted");
// Load the function pointer.
llvm::Value *FnPtr = Builder.CreateStructGEP(MemFnPtr, 0);
llvm::Value *FnAsInt = Builder.CreateLoad(FnPtr, "memptr.ptr");
// If the LSB in the function pointer is 1, the function pointer points to
// a virtual function.
llvm::Value *IsVirtual;
if (IsARM)
IsVirtual = Builder.CreateAnd(RawAdj, ptrdiff_1);
else
IsVirtual = Builder.CreateAnd(FnAsInt, ptrdiff_1);
IsVirtual = Builder.CreateIsNotNull(IsVirtual, "memptr.isvirtual");
Builder.CreateCondBr(IsVirtual, FnVirtual, FnNonVirtual);
// In the virtual path, the adjustment left 'This' pointing to the
// vtable of the correct base subobject. The "function pointer" is an
// offset within the vtable (+1 for the virtual flag on non-ARM).
CGF.EmitBlock(FnVirtual);
// Cast the adjusted this to a pointer to vtable pointer and load.
const llvm::Type *VTableTy = Builder.getInt8PtrTy();
llvm::Value *VTable = Builder.CreateBitCast(This, VTableTy->getPointerTo());
VTable = Builder.CreateLoad(VTable, "memptr.vtable");
// Apply the offset.
llvm::Value *VTableOffset = FnAsInt;
if (!IsARM) VTableOffset = Builder.CreateSub(VTableOffset, ptrdiff_1);
VTable = Builder.CreateGEP(VTable, VTableOffset);
// Load the virtual function to call.
VTable = Builder.CreateBitCast(VTable, FTy->getPointerTo()->getPointerTo());
llvm::Value *VirtualFn = Builder.CreateLoad(VTable, "memptr.virtualfn");
CGF.EmitBranch(FnEnd);
// In the non-virtual path, the function pointer is actually a
// function pointer.
CGF.EmitBlock(FnNonVirtual);
llvm::Value *NonVirtualFn =
Builder.CreateIntToPtr(FnAsInt, FTy->getPointerTo(), "memptr.nonvirtualfn");
// We're done.
CGF.EmitBlock(FnEnd);
llvm::PHINode *Callee = Builder.CreatePHI(FTy->getPointerTo());
Callee->reserveOperandSpace(2);
Callee->addIncoming(VirtualFn, FnVirtual);
Callee->addIncoming(NonVirtualFn, FnNonVirtual);
return Callee;
}
/// Perform a derived-to-base or base-to-derived member pointer conversion.
void ItaniumCXXABI::EmitMemberPointerConversion(CodeGenFunction &CGF,
const CastExpr *E,
llvm::Value *Src,
llvm::Value *Dest,
bool VolatileDest) {
assert(E->getCastKind() == CastExpr::CK_DerivedToBaseMemberPointer ||
E->getCastKind() == CastExpr::CK_BaseToDerivedMemberPointer);
CGBuilderTy &Builder = CGF.Builder;
const MemberPointerType *SrcTy =
E->getSubExpr()->getType()->getAs<MemberPointerType>();
const MemberPointerType *DestTy = E->getType()->getAs<MemberPointerType>();
const CXXRecordDecl *SrcDecl = SrcTy->getClass()->getAsCXXRecordDecl();
const CXXRecordDecl *DestDecl = DestTy->getClass()->getAsCXXRecordDecl();
llvm::Value *SrcPtr = Builder.CreateStructGEP(Src, 0, "src.ptr");
SrcPtr = Builder.CreateLoad(SrcPtr);
llvm::Value *SrcAdj = Builder.CreateStructGEP(Src, 1, "src.adj");
SrcAdj = Builder.CreateLoad(SrcAdj);
llvm::Value *DstPtr = Builder.CreateStructGEP(Dest, 0, "dst.ptr");
Builder.CreateStore(SrcPtr, DstPtr, VolatileDest);
llvm::Value *DstAdj = Builder.CreateStructGEP(Dest, 1, "dst.adj");
bool DerivedToBase =
E->getCastKind() == CastExpr::CK_DerivedToBaseMemberPointer;
const CXXRecordDecl *BaseDecl, *DerivedDecl;
if (DerivedToBase)
DerivedDecl = SrcDecl, BaseDecl = DestDecl;
else
BaseDecl = SrcDecl, DerivedDecl = DestDecl;
if (llvm::Constant *Adj =
CGF.CGM.GetNonVirtualBaseClassOffset(DerivedDecl,
E->path_begin(),
E->path_end())) {
if (DerivedToBase)
SrcAdj = Builder.CreateSub(SrcAdj, Adj, "adj");
else
SrcAdj = Builder.CreateAdd(SrcAdj, Adj, "adj");
}
Builder.CreateStore(SrcAdj, DstAdj, VolatileDest);
}
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