UBSan: Teach isDerivedFromAtOffset and findBaseAtOffset about vbases

When the __virtual_mask is set, __offset_flags >> __offset_shift yields
an offset into the vtable.  Dereferencing this vtable slot gets us the
vbase offset.

Adjust a test case to verify that this, in fact, works.

Differential Revision: http://reviews.llvm.org/D6074

llvm-svn: 221445

1 files changed, 2 insertions, 1 deletions

diff --git a/compiler-rt/test/ubsan/TestCases/TypeCheck/vptr.cpp b/compiler-rt/test/ubsan/TestCases/TypeCheck/vptr.cpp
index 1e1d67ac369..3a6b1553f9b 100644
--- a/compiler-rt/test/ubsan/TestCases/TypeCheck/vptr.cpp
+++ b/compiler-rt/test/ubsan/TestCases/TypeCheck/vptr.cpp
@@ -48,7 +48,8 @@ struct T : S {
   virtual int v() { return 1; }
 };
 
-struct U : S, T { virtual int v() { return 2; } };
+struct X {};
+struct U : S, T, virtual X { virtual int v() { return 2; } };
 
 struct V : S {};