this pass claims to preserve scev, make sure to tell it about deletions.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@123247 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/Utils/LoopSimplify.cpp

@@ -268,6 +268,7 @@ ReprocessLoop:
        (PN = dyn_cast<PHINode>(I++)); )
     if (Value *V = SimplifyInstruction(PN, 0, DT)) {
       if (AA) AA->deleteValue(PN);
+      if (SE) SE->forgetValue(PN);
       PN->replaceAllUsesWith(V);
       PN->eraseFromParent();
     }