[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/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
index 7d545e3..79f4a47 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -393,7 +393,7 @@
   unsigned BitWidth = SVT->getPrimitiveSizeInBits();
 
   // If shift-by-zero then just return the original value.
-  if (Count == 0)
+  if (Count.isNullValue())
     return Vec;
 
   // Handle cases when Shift >= BitWidth.
@@ -1395,7 +1395,7 @@
   // If the input to cttz/ctlz is known to be non-zero,
   // then change the 'ZeroIsUndef' parameter to 'true'
   // because we know the zero behavior can't affect the result.
-  if (Known.One != 0 ||
+  if (!Known.One.isNullValue() ||
       isKnownNonZero(Op0, IC.getDataLayout(), 0, &IC.getAssumptionCache(), &II,
                      &IC.getDominatorTree())) {
     if (!match(II.getArgOperand(1), m_One())) {