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));
 }