[MS-ABI] Implement dynamic_cast
This patch implements call lower from dynamic_cast to __RTDynamicCast
and __RTCastToVoid. Test cases are included. A feature of note is that
helper function getPolymorphicOffset is placed in such a way that it can
be used by EmitTypeid (to be implemented in a later patch) without being
moved. Details are included as comments directly in the code.
llvm-svn: 210377
diff --git a/clang/lib/CodeGen/CGExprCXX.cpp b/clang/lib/CodeGen/CGExprCXX.cpp
index f2332bd..268f4aa 100644
--- a/clang/lib/CodeGen/CGExprCXX.cpp
+++ b/clang/lib/CodeGen/CGExprCXX.cpp
@@ -1628,6 +1628,20 @@
CGF.Builder.CreateUnreachable();
}
+/// \brief Gets the offset to the virtual base that contains the vfptr for
+/// MS-ABI polymorphic types.
+static llvm::Value *getPolymorphicOffset(CodeGenFunction &CGF,
+ const CXXRecordDecl *RD,
+ llvm::Value *Value) {
+ const ASTContext &Context = RD->getASTContext();
+ for (const CXXBaseSpecifier &Base : RD->vbases())
+ if (Context.getASTRecordLayout(Base.getType()->getAsCXXRecordDecl())
+ .hasExtendableVFPtr())
+ return CGF.CGM.getCXXABI().GetVirtualBaseClassOffset(
+ CGF, Value, RD, Base.getType()->getAsCXXRecordDecl());
+ llvm_unreachable("One of our vbases should be polymorphic.");
+}
+
static llvm::Value *EmitTypeidFromVTable(CodeGenFunction &CGF,
const Expr *E,
llvm::Type *StdTypeInfoPtrTy) {
@@ -1686,7 +1700,7 @@
StdTypeInfoPtrTy);
}
-static llvm::Constant *getDynamicCastFn(CodeGenFunction &CGF) {
+static llvm::Constant *getItaniumDynamicCastFn(CodeGenFunction &CGF) {
// void *__dynamic_cast(const void *sub,
// const abi::__class_type_info *src,
// const abi::__class_type_info *dst,
@@ -1774,7 +1788,7 @@
}
static llvm::Value *
-EmitDynamicCastCall(CodeGenFunction &CGF, llvm::Value *Value,
+EmitItaniumDynamicCastCall(CodeGenFunction &CGF, llvm::Value *Value,
QualType SrcTy, QualType DestTy,
llvm::BasicBlock *CastEnd) {
llvm::Type *PtrDiffLTy =
@@ -1834,7 +1848,7 @@
Value = CGF.EmitCastToVoidPtr(Value);
llvm::Value *args[] = { Value, SrcRTTI, DestRTTI, OffsetHint };
- Value = CGF.EmitNounwindRuntimeCall(getDynamicCastFn(CGF), args);
+ Value = CGF.EmitNounwindRuntimeCall(getItaniumDynamicCastFn(CGF), args);
Value = CGF.Builder.CreateBitCast(Value, DestLTy);
/// C++ [expr.dynamic.cast]p9:
@@ -1867,8 +1881,125 @@
return llvm::UndefValue::get(DestLTy);
}
+namespace {
+struct MSDynamicCastBuilder {
+ MSDynamicCastBuilder(CodeGenFunction &CGF, const CXXDynamicCastExpr *DCE);
+ llvm::Value *emitDynamicCastCall(llvm::Value *Value);
+ llvm::Value *emitDynamicCast(llvm::Value *Value);
+
+ CodeGenFunction &CGF;
+ CGBuilderTy &Builder;
+ llvm::PointerType *Int8PtrTy;
+ QualType SrcTy, DstTy;
+ const CXXRecordDecl *SrcDecl;
+ bool IsPtrCast, IsCastToVoid, IsCastOfNull;
+};
+} // namespace
+
+MSDynamicCastBuilder::MSDynamicCastBuilder(CodeGenFunction &CGF,
+ const CXXDynamicCastExpr *DCE)
+ : CGF(CGF), Builder(CGF.Builder), Int8PtrTy(CGF.Int8PtrTy),
+ SrcDecl(nullptr) {
+ DstTy = DCE->getTypeAsWritten();
+ IsPtrCast = DstTy->isPointerType();
+ // Get the PointeeTypes. After this point the original types are not used.
+ DstTy = IsPtrCast ? DstTy->castAs<PointerType>()->getPointeeType()
+ : DstTy->castAs<ReferenceType>()->getPointeeType();
+ IsCastToVoid = DstTy->isVoidType();
+ IsCastOfNull = DCE->isAlwaysNull();
+ if (IsCastOfNull)
+ return;
+ SrcTy = DCE->getSubExpr()->getType();
+ SrcTy = IsPtrCast ? SrcTy->castAs<PointerType>()->getPointeeType() : SrcTy;
+ SrcDecl = SrcTy->getAsCXXRecordDecl();
+ // If we don't need a base adjustment, we don't need a SrcDecl so clear it
+ // here. Later we use the existance of the SrcDecl to determine the need for
+ // a base adjustment.
+ if (CGF.getContext().getASTRecordLayout(SrcDecl).hasExtendableVFPtr())
+ SrcDecl = nullptr;
+}
+
+llvm::Value *MSDynamicCastBuilder::emitDynamicCastCall(llvm::Value *Value) {
+ llvm::IntegerType *Int32Ty = CGF.Int32Ty;
+ llvm::Value *Offset = llvm::ConstantInt::get(Int32Ty, 0);
+ Value = Builder.CreateBitCast(Value, Int8PtrTy);
+ // If we need to perform a base adjustment, do it here.
+ if (SrcDecl) {
+ Offset = getPolymorphicOffset(CGF, SrcDecl, Value);
+ Value = Builder.CreateInBoundsGEP(Value, Offset);
+ Offset = Builder.CreateTrunc(Offset, Int32Ty);
+ }
+ if (IsCastToVoid) {
+ // PVOID __RTCastToVoid(
+ // PVOID inptr)
+ llvm::Type *ArgTypes[] = {Int8PtrTy};
+ llvm::Constant *Function = CGF.CGM.CreateRuntimeFunction(
+ llvm::FunctionType::get(Int8PtrTy, ArgTypes, false), "__RTCastToVoid");
+ llvm::Value *Args[] = {Value};
+ return CGF.EmitRuntimeCall(Function, Args);
+ }
+ // PVOID __RTDynamicCast(
+ // PVOID inptr,
+ // LONG VfDelta,
+ // PVOID SrcType,
+ // PVOID TargetType,
+ // BOOL isReference)
+ llvm::Type *ArgTypes[] = {Int8PtrTy, Int32Ty, Int8PtrTy, Int8PtrTy, Int32Ty};
+ llvm::Constant *Function = CGF.CGM.CreateRuntimeFunction(
+ llvm::FunctionType::get(Int8PtrTy, ArgTypes, false), "__RTDynamicCast");
+ llvm::Value *Args[] = {
+ Value, Offset,
+ CGF.CGM.GetAddrOfRTTIDescriptor(SrcTy.getUnqualifiedType()),
+ CGF.CGM.GetAddrOfRTTIDescriptor(DstTy.getUnqualifiedType()),
+ llvm::ConstantInt::get(Int32Ty, IsPtrCast ? 0 : 1)};
+ return CGF.EmitRuntimeCall(Function, Args);
+}
+
+llvm::Value *MSDynamicCastBuilder::emitDynamicCast(llvm::Value *Value) {
+ // Note about undefined behavior: If the dynamic cast is casting to a
+ // reference type and the input is null, we hit a grey area in the standard.
+ // Here we're interpreting the behavior as undefined. The effects are the
+ // following: If the compiler determines that the argument is statically null
+ // or if the argument is dynamically null but does not require base
+ // adjustment, __RTDynamicCast will be called with a null argument and the
+ // isreference bit set. In this case __RTDynamicCast will throw
+ // std::bad_cast. If the argument is dynamically null and a base adjustment is
+ // required the resulting code will produce an out of bounds memory reference
+ // when trying to read VBTblPtr. In Itanium mode clang also emits a vtable
+ // load that fails at run time.
+ llvm::PointerType *DstLTy = CGF.ConvertType(DstTy)->getPointerTo();
+ if (IsCastOfNull && IsPtrCast)
+ return Builder.CreateBitCast(Value, DstLTy);
+ if (IsCastOfNull || !IsPtrCast || !SrcDecl)
+ return Builder.CreateBitCast(emitDynamicCastCall(Value), DstLTy);
+ // !IsCastOfNull && IsPtrCast && SrcDecl
+ // In this case we have a pointer that requires a base adjustment. An
+ // adjustment is only required if the pointer is actually valid so here we
+ // perform a null check before doing the base adjustment and calling
+ // __RTDynamicCast. In the case that the argument is null we simply return
+ // null without calling __RTDynamicCast.
+ llvm::BasicBlock *EntryBlock = Builder.GetInsertBlock();
+ llvm::BasicBlock *CallBlock = CGF.createBasicBlock("dynamic_cast.valid");
+ llvm::BasicBlock *ExitBlock = CGF.createBasicBlock("dynamic_cast.call");
+ Builder.CreateCondBr(Builder.CreateIsNull(Value), ExitBlock, CallBlock);
+ // Emit the call block and code for it.
+ CGF.EmitBlock(CallBlock);
+ Value = emitDynamicCastCall(Value);
+ // Emit the call block and the phi nodes for it.
+ CGF.EmitBlock(ExitBlock);
+ llvm::PHINode *ValuePHI = Builder.CreatePHI(Int8PtrTy, 2);
+ ValuePHI->addIncoming(Value, CallBlock);
+ ValuePHI->addIncoming(llvm::Constant::getNullValue(Int8PtrTy), EntryBlock);
+ return Builder.CreateBitCast(ValuePHI, DstLTy);
+}
+
llvm::Value *CodeGenFunction::EmitDynamicCast(llvm::Value *Value,
const CXXDynamicCastExpr *DCE) {
+ if (getTarget().getCXXABI().isMicrosoft()) {
+ MSDynamicCastBuilder Builder(*this, DCE);
+ return Builder.emitDynamicCast(Value);
+ }
+
QualType DestTy = DCE->getTypeAsWritten();
if (DCE->isAlwaysNull())
@@ -1894,7 +2025,7 @@
EmitBlock(CastNotNull);
}
- Value = EmitDynamicCastCall(*this, Value, SrcTy, DestTy, CastEnd);
+ Value = EmitItaniumDynamicCastCall(*this, Value, SrcTy, DestTy, CastEnd);
if (ShouldNullCheckSrcValue) {
EmitBranch(CastEnd);