[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/Transforms/InstCombine/InstCombinePHI.cpp b/llvm/lib/Transforms/InstCombine/InstCombinePHI.cpp
index 5dbf1e8..987291f 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombinePHI.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombinePHI.cpp
@@ -639,7 +639,7 @@
   assert(isa<IntegerType>(PN.getType()) && "Expect only intger type phi");
   for (Value *V : PN.operands())
     if (auto *ConstVA = dyn_cast<ConstantInt>(V))
-      if (!ConstVA->isZeroValue())
+      if (!ConstVA->isZero())
         return ConstVA;
   return ConstantInt::get(cast<IntegerType>(PN.getType()), 1);
 }