[ms] Fix vbtable index for covariant overrides of vbase methods

Overriding a method from a virtual base with a covariant return type
consumes a slot from the vftable in the virtual base. This can make it
impossible to implement certain diamond inheritance hierarchies, but we
have to follow along for compatibility in the simple cases.

This patch only affects our vtable dumper and member pointer function
mangling, since all other callers of getMethodVFTableLocation seem to
recompute VBTableIndex instead of using the one in the method location.

Patch by David Majnemer

llvm-svn: 312017

1 files changed, 6 insertions, 4 deletions

diff --git a/clang/lib/AST/VTableBuilder.cpp b/clang/lib/AST/VTableBuilder.cpp
index e60ae33f2e5..ae8f6309fc6 100644
--- a/clang/lib/AST/VTableBuilder.cpp
+++ b/clang/lib/AST/VTableBuilder.cpp
@@ -2963,6 +2963,9 @@ void VFTableBuilder::AddMethods(BaseSubobject Base, unsigned BaseDepth,
       CalculateVtordispAdjustment(FinalOverrider, ThisOffset,
                                   ThisAdjustmentOffset);
 
+    unsigned VBIndex =
+        LastVBase ? VTables.getVBTableIndex(MostDerivedClass, LastVBase) : 0;
+
     if (OverriddenMD) {
       // If MD overrides anything in this vftable, we need to update the
       // entries.
@@ -2975,6 +2978,8 @@ void VFTableBuilder::AddMethods(BaseSubobject Base, unsigned BaseDepth,
 
       MethodInfo &OverriddenMethodInfo = OverriddenMDIterator->second;
 
+      VBIndex = OverriddenMethodInfo.VBTableIndex;
+
       // Let's check if the overrider requires any return adjustments.
       // We must create a new slot if the MD's return type is not trivially
       // convertible to the OverriddenMD's one.
@@ -2987,8 +2992,7 @@ void VFTableBuilder::AddMethods(BaseSubobject Base, unsigned BaseDepth,
       if (!ReturnAdjustingThunk) {
         // No return adjustment needed - just replace the overridden method info
         // with the current info.
-        MethodInfo MI(OverriddenMethodInfo.VBTableIndex,
-                      OverriddenMethodInfo.VFTableIndex);
+        MethodInfo MI(VBIndex, OverriddenMethodInfo.VFTableIndex);
         MethodInfoMap.erase(OverriddenMDIterator);
 
         assert(!MethodInfoMap.count(MD) &&
@@ -3015,8 +3019,6 @@ void VFTableBuilder::AddMethods(BaseSubobject Base, unsigned BaseDepth,
 
     // If we got here, MD is a method not seen in any of the sub-bases or
     // it requires return adjustment. Insert the method info for this method.
-    unsigned VBIndex =
-        LastVBase ? VTables.getVBTableIndex(MostDerivedClass, LastVBase) : 0;
     MethodInfo MI(VBIndex,
                   HasRTTIComponent ? Components.size() - 1 : Components.size(),
                   ReturnAdjustingThunk);