MS ABI: Include the vfptr offset in memptrs to virtual methods

Virtual methods expect 'this' to point to the vfptr containing the
virtual method, and this extends to virtual member pointer thunks.  The
relevant vfptr is always at offset zero on entry to the thunk, and no
this adjustment is needed.

Previously we would not include the vfptr adjustment in the member
pointer, and we'd look at the vfptr offset when loading from the vftable
in the thunk.

Fixes PR18917.

llvm-svn: 201835

1 files changed, 22 insertions, 13 deletions

diff --git a/clang/lib/CodeGen/MicrosoftCXXABI.cpp b/clang/lib/CodeGen/MicrosoftCXXABI.cpp
index 57ad9fb1ad9..7e3cf4f2000 100644
--- a/clang/lib/CodeGen/MicrosoftCXXABI.cpp
+++ b/clang/lib/CodeGen/MicrosoftCXXABI.cpp
@@ -328,8 +328,9 @@ private:
   const VBTableGlobals &enumerateVBTables(const CXXRecordDecl *RD);
 
   /// \brief Generate a thunk for calling a virtual member function MD.
-  llvm::Function *EmitVirtualMemPtrThunk(const CXXMethodDecl *MD,
-                                         StringRef ThunkName);
+  llvm::Function *EmitVirtualMemPtrThunk(
+      const CXXMethodDecl *MD,
+      const MicrosoftVTableContext::MethodVFTableLocation &ML);
 
 public:
   virtual llvm::Type *ConvertMemberPointerType(const MemberPointerType *MPT);
@@ -1015,9 +1016,15 @@ MicrosoftCXXABI::enumerateVBTables(const CXXRecordDecl *RD) {
   return VBGlobals;
 }
 
-llvm::Function *
-MicrosoftCXXABI::EmitVirtualMemPtrThunk(const CXXMethodDecl *MD,
-                                        StringRef ThunkName) {
+llvm::Function *MicrosoftCXXABI::EmitVirtualMemPtrThunk(
+    const CXXMethodDecl *MD,
+    const MicrosoftVTableContext::MethodVFTableLocation &ML) {
+  // Calculate the mangled name.
+  SmallString<256> ThunkName;
+  llvm::raw_svector_ostream Out(ThunkName);
+  getMangleContext().mangleVirtualMemPtrThunk(MD, Out);
+  Out.flush();
+
   // If the thunk has been generated previously, just return it.
   if (llvm::GlobalValue *GV = CGM.getModule().getNamedValue(ThunkName))
     return cast<llvm::Function>(GV);
@@ -1041,9 +1048,14 @@ MicrosoftCXXABI::EmitVirtualMemPtrThunk(const CXXMethodDecl *MD,
   CodeGenFunction CGF(CGM);
   CGF.StartThunk(ThunkFn, MD, FnInfo);
 
-  // Get to the Callee.
+  // Load the vfptr and then callee from the vftable.  The callee should have
+  // adjusted 'this' so that the vfptr is at offset zero.
   llvm::Value *This = CGF.LoadCXXThis();
-  llvm::Value *Callee = getVirtualFunctionPointer(CGF, MD, This, ThunkTy);
+  llvm::Value *VTable =
+      CGF.GetVTablePtr(This, ThunkTy->getPointerTo()->getPointerTo());
+  llvm::Value *VFuncPtr =
+      CGF.Builder.CreateConstInBoundsGEP1_64(VTable, ML.Index, "vfn");
+  llvm::Value *Callee = CGF.Builder.CreateLoad(VFuncPtr);
 
   // Make the call and return the result.
   CGF.EmitCallAndReturnForThunk(MD, Callee, 0);
@@ -1523,13 +1535,10 @@ MicrosoftCXXABI::BuildMemberPointer(const CXXRecordDecl *RD,
                                "member function in virtual base class");
       FirstField = llvm::Constant::getNullValue(CGM.VoidPtrTy);
     } else {
-      SmallString<256> ThunkName;
-      llvm::raw_svector_ostream Out(ThunkName);
-      getMangleContext().mangleVirtualMemPtrThunk(MD, Out);
-      Out.flush();
-
-      llvm::Function *Thunk = EmitVirtualMemPtrThunk(MD, ThunkName.str());
+      llvm::Function *Thunk = EmitVirtualMemPtrThunk(MD, ML);
       FirstField = llvm::ConstantExpr::getBitCast(Thunk, CGM.VoidPtrTy);
+      // Include the vfptr adjustment if the method is in a non-primary vftable.
+      NonVirtualBaseAdjustment += ML.VFPtrOffset;
     }
   }