LowerExpectIntrinsic handlePhiDef - silence static analyzer dyn_cast<PHINode> null dereference warning. NFCI.

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

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@373481 91177308-0d34-0410-b5e6-96231b3b80d8

Author: RKSimon

lib/Transforms/Scalar/LowerExpectIntrinsic.cpp

@@ -161,7 +161,7 @@ static void handlePhiDef(CallInst *Expect) {
     return Result;
   };
 
-  auto *PhiDef = dyn_cast<PHINode>(V);
+  auto *PhiDef = cast<PHINode>(V);
 
   // Get the first dominating conditional branch of the operand
   // i's incoming block.