[InstCombine][InstSimplify] Use APInt::isNullValue/isOneValue to reduce compiled code for comparing APInts with 0 and 1. NFC

These methods are specifically optimized to only counting leading zeros without an additional uint64_t compare.

llvm-svn: 304876
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
index 4d40835..2fcfe46 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
@@ -930,7 +930,7 @@
         }
       }
 
-      if (*C2 != 0) // avoid X udiv 0
+      if (!C2->isNullValue()) // avoid X udiv 0
         if (Instruction *FoldedDiv = foldOpWithConstantIntoOperand(I))
           return FoldedDiv;
     }