[PATCH] [MS ABI] Error instead of generating bad vftables for certain virtual hierarchies (PR18967)

[Hans Wennborg]

Hi rnk,

It's not pretty, but this allows us to fall back instead of miscompiling stuff.

http://llvm-reviews.chandlerc.com/D2890

Files:
  lib/AST/VTableBuilder.cpp
  test/CodeGenCXX/microsoft-abi-virtual-inheritance.cpp
  test/CodeGenCXX/microsoft-abi-vtables-virtual-inheritance-pr18967.cpp

Index: lib/AST/VTableBuilder.cpp
===================================================================
--- lib/AST/VTableBuilder.cpp
+++ lib/AST/VTableBuilder.cpp
@@ -2560,10 +2560,52 @@
                   const CXXRecordDecl *LastVBase,
                   BasesSetVectorTy &VisitedBases);
 
+  void CheckPR18967() {
+    // PR18967: We fail at this-adjustment for virtual methods inherited from
+    // non-primary non-vritual bases the overrides a method in a virtual base.
+
+    if (Context.getLangOpts().DumpVTableLayouts)
+      return;
+    const ASTRecordLayout &Layout = Context.getASTRecordLayout(
+        MostDerivedClass);
+    for (CXXRecordDecl::base_class_const_iterator BI =
+        MostDerivedClass->bases_begin(), BE = MostDerivedClass->bases_end();
+        BI != BE; ++BI) {
+      const CXXRecordDecl *Base = BI->getType()->getAsCXXRecordDecl();
+      if (Base == Layout.getPrimaryBase())
+        continue;
+      if (BI->isVirtual())
+        continue;
+      for (CXXRecordDecl::method_iterator I = Base->method_begin(),
+          E = Base->method_end(); I != E; ++I) {
+        const CXXMethodDecl *Method = *I;
+        if (!Method->isVirtual())
+          continue;
+        if (isa<CXXDestructorDecl>(Method))
+          continue;
+        OverriddenMethodsSetTy OverriddenMethods;
+        ComputeAllOverriddenMethods(Method, OverriddenMethods);
+        for (OverriddenMethodsSetTy::const_iterator I =
+            OverriddenMethods.begin(),
+            E = OverriddenMethods.end(); I != E; ++I) {
+          const CXXMethodDecl *Overridden = *I;
+          if (Base->isVirtuallyDerivedFrom(Overridden->getParent())) {
+            ErrorUnsupported("classes with non-primary non-virtual base "
+                "classes that override methods in virtual bases",
+                BI->getLocStart());
+            return;
+          }
+        }
+      }
+    }
+  }
+
   void LayoutVFTable() {
     // FIXME: add support for RTTI when we have proper LLVM support for symbols
     // pointing to the middle of a section.
 
+    CheckPR18967();
+
     BasesSetVectorTy VisitedBases;
     AddMethods(BaseSubobject(MostDerivedClass, CharUnits::Zero()), 0, 0,
                VisitedBases);
Index: test/CodeGenCXX/microsoft-abi-virtual-inheritance.cpp
===================================================================
--- test/CodeGenCXX/microsoft-abi-virtual-inheritance.cpp
+++ test/CodeGenCXX/microsoft-abi-virtual-inheritance.cpp
@@ -217,7 +217,12 @@
   // CHECK: ret
 }
 
-struct C : B {
+struct X : virtual VBase {
+  int x;
+};
+
+
+struct C : X {
   C();
   // has an implicit vdtor.
 };
Index: test/CodeGenCXX/microsoft-abi-vtables-virtual-inheritance-pr18967.cpp
===================================================================
--- /dev/null
+++ test/CodeGenCXX/microsoft-abi-vtables-virtual-inheritance-pr18967.cpp
@@ -0,0 +1,27 @@
+// RUN: not %clang_cc1 -triple i686-pc-win32 -emit-llvm -fno-rtti %s 2>&1 | FileCheck %s
+
+// CHECK: error: v-table layout for classes with non-primary non-virtual base classes that override methods in virtual bases is not supported yet
+
+struct A {
+  virtual int foo() { return a; }
+  int a;
+};
+struct B : virtual A {
+  B() : b(1) {}
+  virtual int bar() { return b; }
+  int b;
+};
+struct C : virtual A {
+  C() : c(2) {}
+  virtual int foo() { return c; }
+  int c;
+};
+struct D : B, C {
+  D() : d(3) {}
+  virtual int bar() { return d; }
+  int d;
+};
+int main() {
+  D d;
+  return d.foo();
+}
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