IRGen: When performing CFI checks, load vtable pointer from vbase when necessary.

Under the Microsoft ABI, it is possible for an object not to have
a virtual table pointer of its own if all of its virtual functions
were introduced by virtual bases. In that case, we need to load the
vtable pointer from one of the virtual bases and perform the type
check using its type.

Differential Revision: https://reviews.llvm.org/D41036

llvm-svn: 320638

1 files changed, 22 insertions, 7 deletions

diff --git a/clang/lib/CodeGen/MicrosoftCXXABI.cpp b/clang/lib/CodeGen/MicrosoftCXXABI.cpp
index 97a7fbab9a5..ffb3681c258 100644
--- a/clang/lib/CodeGen/MicrosoftCXXABI.cpp
+++ b/clang/lib/CodeGen/MicrosoftCXXABI.cpp
@@ -578,7 +578,7 @@ private:
     return GetVBaseOffsetFromVBPtr(CGF, Base, VBPOffset, VBTOffset, VBPtr);
   }
 
-  std::pair<Address, llvm::Value *>
+  std::tuple<Address, llvm::Value *, const CXXRecordDecl *>
   performBaseAdjustment(CodeGenFunction &CGF, Address Value,
                         QualType SrcRecordTy);
 
@@ -745,6 +745,10 @@ public:
 
   llvm::GlobalVariable *getThrowInfo(QualType T) override;
 
+  std::pair<llvm::Value *, const CXXRecordDecl *>
+  LoadVTablePtr(CodeGenFunction &CGF, Address This,
+                const CXXRecordDecl *RD) override;
+
 private:
   typedef std::pair<const CXXRecordDecl *, CharUnits> VFTableIdTy;
   typedef llvm::DenseMap<VFTableIdTy, llvm::GlobalVariable *> VTablesMapTy;
@@ -926,7 +930,7 @@ void MicrosoftCXXABI::emitBeginCatch(CodeGenFunction &CGF,
 /// We need to perform a generic polymorphic operation (like a typeid
 /// or a cast), which requires an object with a vfptr.  Adjust the
 /// address to point to an object with a vfptr.
-std::pair<Address, llvm::Value *>
+std::tuple<Address, llvm::Value *, const CXXRecordDecl *>
 MicrosoftCXXABI::performBaseAdjustment(CodeGenFunction &CGF, Address Value,
                                        QualType SrcRecordTy) {
   Value = CGF.Builder.CreateBitCast(Value, CGF.Int8PtrTy);
@@ -937,7 +941,8 @@ MicrosoftCXXABI::performBaseAdjustment(CodeGenFunction &CGF, Address Value,
   // covers non-virtual base subobjects: a class with its own virtual
   // functions would be a candidate to be a primary base.
   if (Context.getASTRecordLayout(SrcDecl).hasExtendableVFPtr())
-    return std::make_pair(Value, llvm::ConstantInt::get(CGF.Int32Ty, 0));
+    return std::make_tuple(Value, llvm::ConstantInt::get(CGF.Int32Ty, 0),
+                           SrcDecl);
 
   // Okay, one of the vbases must have a vfptr, or else this isn't
   // actually a polymorphic class.
@@ -956,7 +961,7 @@ MicrosoftCXXABI::performBaseAdjustment(CodeGenFunction &CGF, Address Value,
   llvm::Value *Ptr = CGF.Builder.CreateInBoundsGEP(Value.getPointer(), Offset);
   CharUnits VBaseAlign =
     CGF.CGM.getVBaseAlignment(Value.getAlignment(), SrcDecl, PolymorphicBase);
-  return std::make_pair(Address(Ptr, VBaseAlign), Offset);
+  return std::make_tuple(Address(Ptr, VBaseAlign), Offset, PolymorphicBase);
 }
 
 bool MicrosoftCXXABI::shouldTypeidBeNullChecked(bool IsDeref,
@@ -987,7 +992,7 @@ llvm::Value *MicrosoftCXXABI::EmitTypeid(CodeGenFunction &CGF,
                                          QualType SrcRecordTy,
                                          Address ThisPtr,
                                          llvm::Type *StdTypeInfoPtrTy) {
-  std::tie(ThisPtr, std::ignore) =
+  std::tie(ThisPtr, std::ignore, std::ignore) =
       performBaseAdjustment(CGF, ThisPtr, SrcRecordTy);
   auto Typeid = emitRTtypeidCall(CGF, ThisPtr.getPointer()).getInstruction();
   return CGF.Builder.CreateBitCast(Typeid, StdTypeInfoPtrTy);
@@ -1011,7 +1016,8 @@ llvm::Value *MicrosoftCXXABI::EmitDynamicCastCall(
       CGF.CGM.GetAddrOfRTTIDescriptor(DestRecordTy.getUnqualifiedType());
 
   llvm::Value *Offset;
-  std::tie(This, Offset) = performBaseAdjustment(CGF, This, SrcRecordTy);
+  std::tie(This, Offset, std::ignore) =
+      performBaseAdjustment(CGF, This, SrcRecordTy);
   llvm::Value *ThisPtr = This.getPointer();
   Offset = CGF.Builder.CreateTrunc(Offset, CGF.Int32Ty);
 
@@ -1037,7 +1043,8 @@ llvm::Value *
 MicrosoftCXXABI::EmitDynamicCastToVoid(CodeGenFunction &CGF, Address Value,
                                        QualType SrcRecordTy,
                                        QualType DestTy) {
-  std::tie(Value, std::ignore) = performBaseAdjustment(CGF, Value, SrcRecordTy);
+  std::tie(Value, std::ignore, std::ignore) =
+      performBaseAdjustment(CGF, Value, SrcRecordTy);
 
   // PVOID __RTCastToVoid(
   //   PVOID inptr)
@@ -4244,3 +4251,11 @@ void MicrosoftCXXABI::emitThrow(CodeGenFunction &CGF, const CXXThrowExpr *E) {
   };
   CGF.EmitNoreturnRuntimeCallOrInvoke(getThrowFn(), Args);
 }
+
+std::pair<llvm::Value *, const CXXRecordDecl *>
+MicrosoftCXXABI::LoadVTablePtr(CodeGenFunction &CGF, Address This,
+                               const CXXRecordDecl *RD) {
+  std::tie(This, std::ignore, RD) =
+      performBaseAdjustment(CGF, This, QualType(RD->getTypeForDecl(), 0));
+  return {CGF.GetVTablePtr(This, CGM.Int8PtrTy, RD), RD};
+}