From: Dan Gohman <gohman@apple.com>
Date: Tue, 20 Jul 2010 16:53:00 +0000 (+0000)
Subject: Add a fast path for x - x.
X-Git-Url: http://plrg.eecs.uci.edu/git/?p=oota-llvm.git;a=commitdiff_plain;h=eb4152c192ad226a1dee825f1433277e1851edbc

Add a fast path for x - x.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@108855 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Analysis/ScalarEvolution.cpp b/lib/Analysis/ScalarEvolution.cpp
index f0bc9360b16..179aa8867d6 100644
--- a/lib/Analysis/ScalarEvolution.cpp
+++ b/lib/Analysis/ScalarEvolution.cpp
@@ -2442,6 +2442,10 @@ const SCEV *ScalarEvolution::getNotSCEV(const SCEV *V) {
 ///
 const SCEV *ScalarEvolution::getMinusSCEV(const SCEV *LHS,
                                           const SCEV *RHS) {
+  // Fast path: X - X --> 0.
+  if (LHS == RHS)
+    return getConstant(LHS->getType(), 0);
+
   // X - Y --> X + -Y
   return getAddExpr(LHS, getNegativeSCEV(RHS));
 }