IndVarSimplify - silence static analyzer dyn_cast<> null dereference warning. NFCI.

The static analyzer is warning about a potential null dereference, but we should be able to use cast<> directly and if not assert will fire for us.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@375426 91177308-0d34-0410-b5e6-96231b3b80d8

Author: RKSimon

lib/Transforms/Scalar/IndVarSimplify.cpp

@@ -2268,8 +2268,8 @@ static PHINode *FindLoopCounter(Loop *L, BasicBlock *ExitingBB,
     if (BECount->getType()->isPointerTy() && !Phi->getType()->isPointerTy())
       continue;
 
-    const auto *AR = dyn_cast<SCEVAddRecExpr>(SE->getSCEV(Phi));
-    
+    const auto *AR = cast<SCEVAddRecExpr>(SE->getSCEV(Phi));
+
     // AR may be a pointer type, while BECount is an integer type.
     // AR may be wider than BECount. With eq/ne tests overflow is immaterial.
     // AR may not be a narrower type, or we may never exit.