[Constants] If we already have a ConstantInt*, prefer to use isZero/isOne/isMinusOne instead of isNullValue/isOneValue/isAllOnesValue inherited from Constant. NFCI

Going through the Constant methods requires redetermining that the Constant is a ConstantInt and then calling isZero/isOne/isMinusOne.

llvm-svn: 307292
diff --git a/llvm/lib/Analysis/VectorUtils.cpp b/llvm/lib/Analysis/VectorUtils.cpp
index 0ace8fa..554d132 100644
--- a/llvm/lib/Analysis/VectorUtils.cpp
+++ b/llvm/lib/Analysis/VectorUtils.cpp
@@ -301,7 +301,7 @@
   auto *InsertEltInst =
     dyn_cast<InsertElementInst>(ShuffleInst->getOperand(0));
   if (!InsertEltInst || !isa<ConstantInt>(InsertEltInst->getOperand(2)) ||
-      !cast<ConstantInt>(InsertEltInst->getOperand(2))->isNullValue())
+      !cast<ConstantInt>(InsertEltInst->getOperand(2))->isZero())
     return nullptr;
 
   return InsertEltInst->getOperand(1);