[SCEV] Introduce ScalarEvolution::getOne and getZero.

Summary:
It is fairly common to call SE->getConstant(Ty, 0) or
SE->getConstant(Ty, 1); this change makes such uses a little bit
briefer.

I've refactored the call sites I could find easily to use getZero /
getOne.

Reviewers: hfinkel, majnemer, reames

Subscribers: sanjoy, llvm-commits

Differential Revision: http://reviews.llvm.org/D12947

llvm-svn: 248362
diff --git a/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp b/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp
index 1055484..cb481c1 100644
--- a/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp
@@ -253,8 +253,7 @@
     Rem->replaceAllUsesWith(Rem->getOperand(0));
   else {
     // (i+1) % n  -->  (i+1)==n?0:(i+1)  if i is in [0,n).
-    const SCEV *LessOne =
-      SE->getMinusSCEV(S, SE->getConstant(S->getType(), 1));
+    const SCEV *LessOne = SE->getMinusSCEV(S, SE->getOne(S->getType()));
     if (IsSigned && !SE->isKnownNonNegative(LessOne))
       return;