Add a fast path for x - x.

llvm-svn: 108855
2010-07-20 16:53:00 +00:00 · 2010-07-20 16:53:00 +00:00 · 46f00a25f9
parent 1804d30cf1
commit 46f00a25f9
1 changed files with 4 additions and 0 deletions
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/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));
 }