1 files changed, 21 insertions, 5 deletions
diff --git a/clang/lib/AST/VTableBuilder.cpp b/clang/lib/AST/VTableBuilder.cpp
index 3e7871e7bd7..a95791ce884 100644
--- a/clang/lib/AST/VTableBuilder.cpp
+++ b/clang/lib/AST/VTableBuilder.cpp
@@ -3544,6 +3544,19 @@ static void computeFullPathsForVFTables(ASTContext &Context,
   }
 }
 
+static bool
+vfptrIsEarlierInMDC(const ASTRecordLayout &Layout,
+                    const MicrosoftVTableContext::MethodVFTableLocation &LHS,
+                    const MicrosoftVTableContext::MethodVFTableLocation &RHS) {
+  CharUnits L = LHS.VFPtrOffset;
+  CharUnits R = RHS.VFPtrOffset;
+  if (LHS.VBase)
+    L += Layout.getVBaseClassOffset(LHS.VBase);
+  if (RHS.VBase)
+    R += Layout.getVBaseClassOffset(RHS.VBase);
+  return L < R;
+}
+
 void MicrosoftVTableContext::computeVTableRelatedInformation(
     const CXXRecordDecl *RD) {
   assert(RD->isDynamicClass());
@@ -3574,12 +3587,15 @@ void MicrosoftVTableContext::computeVTableRelatedInformation(
         EmptyAddressPointsMap);
     Thunks.insert(Builder.thunks_begin(), Builder.thunks_end());
 
+    const ASTRecordLayout &Layout = Context.getASTRecordLayout(RD);
     for (const auto &Loc : Builder.vtable_locations()) {
-      GlobalDecl GD = Loc.first;
-      MethodVFTableLocation NewLoc = Loc.second;
-      auto M = NewMethodLocations.find(GD);
-      if (M == NewMethodLocations.end() || NewLoc < M->second)
-        NewMethodLocations[GD] = NewLoc;
+      auto Insert = NewMethodLocations.insert(Loc);
+      if (!Insert.second) {
+        const MethodVFTableLocation &NewLoc = Loc.second;
+        MethodVFTableLocation &OldLoc = Insert.first->second;
+        if (vfptrIsEarlierInMDC(Layout, NewLoc, OldLoc))
+          OldLoc = NewLoc;
+      }
     }
   }