MS ABI: Don't append to vbtables that we shouldn't extend

This was probably a benign bug, since nobody would look at the vbtable
slots that we were filling in.

llvm-svn: 206508

2 files changed, 19 insertions, 9 deletions

diff --git a/clang/lib/AST/VTableBuilder.cpp b/clang/lib/AST/VTableBuilder.cpp
index 3e8dd470dfe..c606450e1e1 100644
--- a/clang/lib/AST/VTableBuilder.cpp
+++ b/clang/lib/AST/VTableBuilder.cpp
@@ -3180,11 +3180,7 @@ void MicrosoftVTableContext::computeVTablePaths(bool ForVBTables,
     const VPtrInfoVector &BasePaths =
         ForVBTables ? enumerateVBTables(Base) : getVFPtrOffsets(Base);
 
-    for (VPtrInfoVector::const_iterator II = BasePaths.begin(),
-                                        EE = BasePaths.end();
-         II != EE; ++II) {
-      VPtrInfo *BaseInfo = *II;
-
+    for (VPtrInfo *BaseInfo : BasePaths) {
       // Don't include the path if it goes through a virtual base that we've
       // already included.
       if (setsIntersect(VBasesSeen, BaseInfo->ContainingVBases))
@@ -3202,12 +3198,16 @@ void MicrosoftVTableContext::computeVTablePaths(bool ForVBTables,
       // FIXME: Why do we need this?
       P->PathToBaseWithVPtr.insert(P->PathToBaseWithVPtr.begin(), Base);
 
-      // Keep track of which derived class ultimately uses the vtable, and what
-      // the full adjustment is from the MDC to this vtable.  The adjustment is
-      // captured by an optional vbase and a non-virtual offset.
-      if (Base == (ForVBTables ? Layout.getBaseSharingVBPtr()
+      // Keep track of which vtable the derived class is going to extend with
+      // new methods or bases.  We append to either the vftable of our primary
+      // base, or the first non-virtual base that has a vbtable.
+      if (P->ReusingBase == Base &&
+          Base == (ForVBTables ? Layout.getBaseSharingVBPtr()
                                : Layout.getPrimaryBase()))
         P->ReusingBase = RD;
+
+      // Keep track of the full adjustment from the MDC to this vtable.  The
+      // adjustment is captured by an optional vbase and a non-virtual offset.
       if (B.isVirtual())
         P->ContainingVBases.push_back(Base);
       else if (P->ContainingVBases.empty())
diff --git a/clang/test/CodeGenCXX/microsoft-abi-vbtables.cpp b/clang/test/CodeGenCXX/microsoft-abi-vbtables.cpp
index b950d0cbf0c..8b86d6bd3c8 100644
--- a/clang/test/CodeGenCXX/microsoft-abi-vbtables.cpp
+++ b/clang/test/CodeGenCXX/microsoft-abi-vbtables.cpp
@@ -518,3 +518,13 @@ F x;
 // CHECK-DAG: @"\01??_8F@Test28@@7BD@1@@" =
 // CHECK-DAG: @"\01??_8F@Test28@@7BE@1@@" =
 }
+
+namespace Test29 {
+struct A {};
+struct B : virtual A {};
+struct C : virtual B {};
+struct D : C {};
+D d;
+
+// CHECK-DAG: @"\01??_8D@Test29@@7BB@1@@" = linkonce_odr unnamed_addr constant [2 x i32] zeroinitializer
+}