Teach ConstantFolding to do a better job when folding gep(bitcast).

This permits the devirtualization of llvm.org/PR3100#c9 when compiled by clang.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@90099 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Analysis/ConstantFolding.cpp

@@ -564,6 +564,7 @@ static Constant *SymbolicallyEvaluateGEP(Constant *const *Ops, unsigned NumOps,
   // we eliminate over-indexing of the notional static type array bounds.
   // This makes it easy to determine if the getelementptr is "inbounds".
   // Also, this helps GlobalOpt do SROA on GlobalVariables.
+  Ptr = cast<Constant>(Ptr->stripPointerCasts());
   const Type *Ty = Ptr->getType();
   SmallVector<Constant*, 32> NewIdxs;
   do {