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

4 files changed, 50 insertions, 1 deletions

diff --git a/clang/lib/CodeGen/CGCXXABI.h b/clang/lib/CodeGen/CGCXXABI.h
index a0dcdfdcc68..ffe70be2ca5 100644
--- a/clang/lib/CodeGen/CGCXXABI.h
+++ b/clang/lib/CodeGen/CGCXXABI.h
@@ -154,6 +154,15 @@ protected:
   llvm::Constant *getMemberPointerAdjustment(const CastExpr *E);
 
 public:
+  /// Adjust the given non-null pointer to an object of polymorphic
+  /// type to point to the complete object.
+  ///
+  /// The IR type of the result should be a pointer but is otherwise
+  /// irrelevant.
+  virtual llvm::Value *adjustToCompleteObject(CodeGenFunction &CGF,
+                                              llvm::Value *ptr,
+                                              QualType type) = 0;
+
   /// Build the signature of the given constructor variant by adding
   /// any required parameters.  For convenience, ResTy has been
   /// initialized to 'void', and ArgTys has been initialized with the
diff --git a/clang/lib/CodeGen/CGExprCXX.cpp b/clang/lib/CodeGen/CGExprCXX.cpp
index 3aa5e747812..7276440a47a 100644
--- a/clang/lib/CodeGen/CGExprCXX.cpp
+++ b/clang/lib/CodeGen/CGExprCXX.cpp
@@ -1382,8 +1382,14 @@ static void EmitObjectDelete(CodeGenFunction &CGF,
         if (UseGlobalDelete) {
           // If we're supposed to call the global delete, make sure we do so
           // even if the destructor throws.
+
+          // Derive the complete-object pointer, which is what we need
+          // to pass to the deallocation function.
+          llvm::Value *completePtr =
+            CGF.CGM.getCXXABI().adjustToCompleteObject(CGF, Ptr, ElementType);
+
           CGF.EHStack.pushCleanup<CallObjectDelete>(NormalAndEHCleanup,
-                                                    Ptr, OperatorDelete, 
+                                                    completePtr, OperatorDelete,
                                                     ElementType);
         }
         
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,
diff --git a/clang/lib/CodeGen/MicrosoftCXXABI.cpp b/clang/lib/CodeGen/MicrosoftCXXABI.cpp
index b000c68a952..2c8173ba384 100644
--- a/clang/lib/CodeGen/MicrosoftCXXABI.cpp
+++ b/clang/lib/CodeGen/MicrosoftCXXABI.cpp
@@ -30,6 +30,10 @@ public:
 
   StringRef GetPureVirtualCallName() { return "_purecall"; }
 
+  llvm::Value *adjustToCompleteObject(CodeGenFunction &CGF,
+                                      llvm::Value *ptr,
+                                      QualType type);
+
   void BuildConstructorSignature(const CXXConstructorDecl *Ctor,
                                  CXXCtorType Type,
                                  CanQualType &ResTy,
@@ -95,6 +99,13 @@ public:
 
 }
 
+llvm::Value *MicrosoftCXXABI::adjustToCompleteObject(CodeGenFunction &CGF,
+                                                     llvm::Value *ptr,
+                                                     QualType type) {
+  // FIXME: implement
+  return ptr;
+}
+
 bool MicrosoftCXXABI::needThisReturn(GlobalDecl GD) {
   const CXXMethodDecl* MD = cast<CXXMethodDecl>(GD.getDecl());
   return isa<CXXConstructorDecl>(MD);