[PATCH] Fix PR19066 - 0-sized vftable in the presence of virtual inheritance

[Timur Iskhodzhanov]

Hi rnk, whunt,

Just curious, is there a handy function like isDirectVBase() available somewhere?

http://llvm-reviews.chandlerc.com/D3181

Files:
  lib/AST/VTableBuilder.cpp
  test/CodeGenCXX/microsoft-abi-vtables-virtual-inheritance.cpp

Index: lib/AST/VTableBuilder.cpp
===================================================================
--- lib/AST/VTableBuilder.cpp
+++ lib/AST/VTableBuilder.cpp
@@ -2531,6 +2531,7 @@
     BasesSetVectorTy VisitedBases;
     AddMethods(BaseSubobject(MostDerivedClass, CharUnits::Zero()), 0, 0,
                VisitedBases);
+    assert(Components.size() && "vftable can't be empty");
 
     assert(MethodVFTableLocations.empty());
     for (MethodInfoMapTy::const_iterator I = MethodInfoMap.begin(),
@@ -2793,6 +2794,14 @@
   return false;
 }
 
+static bool isDirectVBase(const CXXRecordDecl *Base, const CXXRecordDecl *RD) {
+  for (const auto &I : RD->bases()) {
+    if (I.isVirtual() && I.getType()->getAsCXXRecordDecl() == Base)
+      return true;
+  }
+  return false;
+}
+
 void VFTableBuilder::AddMethods(BaseSubobject Base, unsigned BaseDepth,
                                 const CXXRecordDecl *LastVBase,
                                 BasesSetVectorTy &VisitedBases) {
@@ -2808,7 +2817,7 @@
   CharUnits NextBaseOffset;
   if (BaseDepth < WhichVFPtr.PathToBaseWithVPtr.size()) {
     NextBase = WhichVFPtr.PathToBaseWithVPtr[BaseDepth];
-    if (Layout.getVBaseOffsetsMap().count(NextBase)) {
+    if (isDirectVBase(NextBase, RD)) {
       NextLastVBase = NextBase;
       NextBaseOffset = MostDerivedClassLayout.getVBaseClassOffset(NextBase);
     } else {
Index: test/CodeGenCXX/microsoft-abi-vtables-virtual-inheritance.cpp
===================================================================
--- test/CodeGenCXX/microsoft-abi-vtables-virtual-inheritance.cpp
+++ test/CodeGenCXX/microsoft-abi-vtables-virtual-inheritance.cpp
@@ -659,3 +659,18 @@
 // MANGLING-DAG: @"\01??_7C at pr17748@@6BA at 1@@"
 // MANGLING-DAG: @"\01??_7C at pr17748@@6BB at 1@@"
 }
+
+namespace pr19066 {
+struct X : virtual B {};
+
+struct Y : virtual X, B {
+  Y();
+  // CHECK-LABEL: VFTable for 'B' in 'pr19066::X' in 'pr19066::Y' (1 entry).
+  // CHECK-NEXT:  0 | void B::g()
+
+  // CHECK-LABEL: VFTable for 'B' in 'pr19066::Y' (1 entry).
+  // CHECK-NEXT:  0 | void B::g()
+};
+
+Y::Y() {}
+}
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