Add AssertingVH which makes PR7647 break consistently.

llvm-svn: 108401

llvm/lib/Analysis/InstructionSimplify.cpp

@@ -443,6 +443,8 @@ void llvm::ReplaceAndSimplifyAllUses(Instruction *From, Value *To,
   // FromHandle - This keeps a weakvh on the from value so that we can know if
   // it gets deleted out from under us in a recursive simplification.
   WeakVH FromHandle(From);
+  // Double-check that To isn't deleted.
+  AssertingVH<> CheckedTo = To;
 
   while (!From->use_empty()) {
     // Update the instruction to use the new value.