fix compile-time issue in spec2017 527.cam4_r

Author: c-rhodes

llvm/lib/Transforms/InstCombine/InstructionCombining.cpp

@@ -5026,6 +5026,9 @@ InstCombinerImpl::pushFreezeToPreventPoisonFromPropagating(FreezeInst &OrigFI) {
       if (U == OrigUse)
         return nullptr;
 
+      if (isa<PoisonValue>(V))
+        continue;
+
       auto *UserI = cast<Instruction>(U->getUser());
       if (auto *PN = dyn_cast<PHINode>(UserI))
         Builder.SetInsertPoint(PN->getIncomingBlock(*U)->getTerminator());