When performing a ::delete of an object with a virtual destructor,

be sure to delete the complete object pointer, not the original
pointer.  This is necessary if the base being deleted is at a
non-zero offset in the complete object.  This is only required
for objects with virtual destructors because deleting an object
via a base-class subobject when the base does not have a virtual
destructor is undefined behavior.

Noticed while reviewing the last four years of cxx-abi-dev
activity.

llvm-svn: 164597

1 files changed, 23 insertions, 0 deletions

diff --git a/clang/lib/CodeGen/ItaniumCXXABI.cpp b/clang/lib/CodeGen/ItaniumCXXABI.cpp
index 5fbff3c253d..877d0d4ae21 100644
--- a/clang/lib/CodeGen/ItaniumCXXABI.cpp
+++ b/clang/lib/CodeGen/ItaniumCXXABI.cpp
@@ -92,6 +92,10 @@ public:
                                           llvm::Value *Addr,
                                           const MemberPointerType *MPT);
 
+  llvm::Value *adjustToCompleteObject(CodeGenFunction &CGF,
+                                      llvm::Value *ptr,
+                                      QualType type);
+
   void BuildConstructorSignature(const CXXConstructorDecl *Ctor,
                                  CXXCtorType T,
                                  CanQualType &ResTy,
@@ -677,6 +681,25 @@ bool ItaniumCXXABI::isZeroInitializable(const MemberPointerType *MPT) {
   return MPT->getPointeeType()->isFunctionType();
 }
 
+/// The Itanium ABI always places an offset to the complete object
+/// at entry -2 in the vtable.
+llvm::Value *ItaniumCXXABI::adjustToCompleteObject(CodeGenFunction &CGF,
+                                                   llvm::Value *ptr,
+                                                   QualType type) {
+  // Grab the vtable pointer as an intptr_t*.
+  llvm::Value *vtable = CGF.GetVTablePtr(ptr, CGF.IntPtrTy->getPointerTo());
+
+  // Track back to entry -2 and pull out the offset there.
+  llvm::Value *offsetPtr = 
+    CGF.Builder.CreateConstInBoundsGEP1_64(vtable, -2, "complete-offset.ptr");
+  llvm::LoadInst *offset = CGF.Builder.CreateLoad(offsetPtr);
+  offset->setAlignment(CGF.PointerAlignInBytes);
+
+  // Apply the offset.
+  ptr = CGF.Builder.CreateBitCast(ptr, CGF.Int8PtrTy);
+  return CGF.Builder.CreateInBoundsGEP(ptr, offset);
+}
+
 /// The generic ABI passes 'this', plus a VTT if it's initializing a
 /// base subobject.
 void ItaniumCXXABI::BuildConstructorSignature(const CXXConstructorDecl *Ctor,