3 files changed, 67 insertions, 0 deletions

diff --git a/clang/lib/CodeGen/CGCXXABI.h b/clang/lib/CodeGen/CGCXXABI.h
index eaeb971dc42..c76769f4252 100644
--- a/clang/lib/CodeGen/CGCXXABI.h
+++ b/clang/lib/CodeGen/CGCXXABI.h
@@ -234,6 +234,12 @@ public:
   virtual llvm::BasicBlock *EmitCtorCompleteObjectHandler(CodeGenFunction &CGF,
                                                           const CXXRecordDecl *RD);
 
+  /// Emit the code to initialize hidden members required
+  /// to handle virtual inheritance, if needed by the ABI.
+  virtual void
+  initializeHiddenVirtualInheritanceMembers(CodeGenFunction &CGF,
+                                            const CXXRecordDecl *RD) {}
+
   /// Emit constructor variants required by this ABI.
   virtual void EmitCXXConstructors(const CXXConstructorDecl *D) = 0;
 
diff --git a/clang/lib/CodeGen/CGClass.cpp b/clang/lib/CodeGen/CGClass.cpp
index 137d793c117..91f42e2f579 100644
--- a/clang/lib/CodeGen/CGClass.cpp
+++ b/clang/lib/CodeGen/CGClass.cpp
@@ -1992,6 +1992,9 @@ void CodeGenFunction::InitializeVTablePointers(const CXXRecordDecl *RD) {
                            /*NearestVBase=*/0, 
                            /*OffsetFromNearestVBase=*/CharUnits::Zero(),
                            /*BaseIsNonVirtualPrimaryBase=*/false, RD, VBases);
+
+  if (RD->getNumVBases())
+    CGM.getCXXABI().initializeHiddenVirtualInheritanceMembers(*this, RD);
 }
 
 llvm::Value *CodeGenFunction::GetVTablePtr(llvm::Value *This,
diff --git a/clang/lib/CodeGen/MicrosoftCXXABI.cpp b/clang/lib/CodeGen/MicrosoftCXXABI.cpp
index 7452c860d0b..fd677712e78 100644
--- a/clang/lib/CodeGen/MicrosoftCXXABI.cpp
+++ b/clang/lib/CodeGen/MicrosoftCXXABI.cpp
@@ -67,6 +67,9 @@ public:
   llvm::BasicBlock *EmitCtorCompleteObjectHandler(CodeGenFunction &CGF,
                                                   const CXXRecordDecl *RD);
 
+  void initializeHiddenVirtualInheritanceMembers(CodeGenFunction &CGF,
+                                                 const CXXRecordDecl *RD);
+
   void EmitCXXConstructors(const CXXConstructorDecl *D);
 
   // Background on MSVC destructors
@@ -456,6 +459,61 @@ MicrosoftCXXABI::EmitCtorCompleteObjectHandler(CodeGenFunction &CGF,
   return SkipVbaseCtorsBB;
 }
 
+void MicrosoftCXXABI::initializeHiddenVirtualInheritanceMembers(
+    CodeGenFunction &CGF, const CXXRecordDecl *RD) {
+  // In most cases, an override for a vbase virtual method can adjust
+  // the "this" parameter by applying a constant offset.
+  // However, this is not enough while a constructor or a destructor of some
+  // class X is being executed if all the following conditions are met:
+  //  - X has virtual bases, (1)
+  //  - X overrides a virtual method M of a vbase Y, (2)
+  //  - X itself is a vbase of the most derived class.
+  //
+  // If (1) and (2) are true, the vtorDisp for vbase Y is a hidden member of X
+  // which holds the extra amount of "this" adjustment we must do when we use
+  // the X vftables (i.e. during X ctor or dtor).
+  // Outside the ctors and dtors, the values of vtorDisps are zero.
+
+  const ASTRecordLayout &Layout = getContext().getASTRecordLayout(RD);
+  typedef ASTRecordLayout::VBaseOffsetsMapTy VBOffsets;
+  const VBOffsets &VBaseMap = Layout.getVBaseOffsetsMap();
+  CGBuilderTy &Builder = CGF.Builder;
+
+  unsigned AS =
+      cast<llvm::PointerType>(getThisValue(CGF)->getType())->getAddressSpace();
+  llvm::Value *Int8This = 0;  // Initialize lazily.
+
+  for (VBOffsets::const_iterator I = VBaseMap.begin(), E = VBaseMap.end();
+        I != E; ++I) {
+    if (!I->second.hasVtorDisp())
+      continue;
+
+    llvm::Value *VBaseOffset = CGM.getCXXABI().GetVirtualBaseClassOffset(
+        CGF, getThisValue(CGF), RD, I->first);
+    // FIXME: it doesn't look right that we SExt in GetVirtualBaseClassOffset()
+    // just to Trunc back immediately.
+    VBaseOffset = Builder.CreateTruncOrBitCast(VBaseOffset, CGF.Int32Ty);
+    uint64_t ConstantVBaseOffset =
+        Layout.getVBaseClassOffset(I->first).getQuantity();
+
+    // vtorDisp_for_vbase = vbptr[vbase_idx] - offsetof(RD, vbase).
+    llvm::Value *VtorDispValue = Builder.CreateSub(
+        VBaseOffset, llvm::ConstantInt::get(CGM.Int32Ty, ConstantVBaseOffset),
+        "vtordisp.value");
+
+    if (!Int8This)
+      Int8This = Builder.CreateBitCast(getThisValue(CGF),
+                                       CGF.Int8Ty->getPointerTo(AS));
+    llvm::Value *VtorDispPtr = Builder.CreateInBoundsGEP(Int8This, VBaseOffset);
+    // vtorDisp is always the 32-bits before the vbase in the class layout.
+    VtorDispPtr = Builder.CreateConstGEP1_32(VtorDispPtr, -4);
+    VtorDispPtr = Builder.CreateBitCast(
+        VtorDispPtr, CGF.Int32Ty->getPointerTo(AS), "vtordisp.ptr");
+
+    Builder.CreateStore(VtorDispValue, VtorDispPtr);
+  }
+}
+
 void MicrosoftCXXABI::EmitCXXConstructors(const CXXConstructorDecl *D) {
   // There's only one constructor type in this ABI.
   CGM.EmitGlobal(GlobalDecl(D, Ctor_Complete));