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 f0bc9360b16d687554fad86b1cde200c80a19402..179aa8867d6d846df1b09bb8f74ef428f0b1c18b 100644 (file)
--- 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) {
 ///
 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));
 }
   // X - Y --> X + -Y
   return getAddExpr(LHS, getNegativeSCEV(RHS));
 }