[SCEV] Update SCEVLoopGuardRewriter to hold reference to map. (NFC)

SCEVLoopGuardRewriter doesn't need to copy the rewrite map. It can just
hold a const reference instead, to avoid an unnecessary copy.

diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index d7effde..5bdbe40 100644 (file)
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -13696,7 +13696,7 @@ ScalarEvolution::computeSymbolicMaxBackedgeTakenCount(const Loop *L) {
 ///
 /// At the moment only rewriting SCEVUnknown is supported.
 class SCEVLoopGuardRewriter : public SCEVRewriteVisitor<SCEVLoopGuardRewriter> {
-  DenseMap<const SCEV *, const SCEV *> Map;
+  const DenseMap<const SCEV *, const SCEV *> &Map;
 
 public:
   SCEVLoopGuardRewriter(ScalarEvolution &SE,