[InstCombine] remove unneeded dyn_cast to prevent unused variable warning

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@325597 91177308-0d34-0410-b5e6-96231b3b80d8

Author: rotateright

lib/Transforms/InstCombine/InstCombineMulDivRem.cpp

@@ -1359,11 +1359,10 @@ Instruction *InstCombiner::visitFDiv(BinaryOperator &I) {
       if (Instruction *R = FoldOpIntoSelect(I, SI))
         return R;
 
-  if (Constant *Op1C = dyn_cast<Constant>(Op1)) {
+  if (isa<Constant>(Op1))
     if (SelectInst *SI = dyn_cast<SelectInst>(Op0))
       if (Instruction *R = FoldOpIntoSelect(I, SI))
         return R;
-  }
 
   if (I.isFast()) {
     Value *X, *Y;