1 files changed, 23 insertions, 0 deletions
diff --git a/llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp b/llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp
index 739ac00..ed08c0b 100644
--- a/llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp
+++ b/llvm/lib/Transforms/Utils/ScalarEvolutionExpander.cpp
@@ -1223,6 +1223,24 @@ Value *SCEVExpander::expandAddRecExprLiterally(const SCEVAddRecExpr *S) {
   return Result;
 }
 
+Value *SCEVExpander::tryToReuseLCSSAPhi(const SCEVAddRecExpr *S) {
+  const Loop *L = S->getLoop();
+  BasicBlock *EB = L->getExitBlock();
+  if (!EB || !EB->getSinglePredecessor() ||
+      !SE.DT.dominates(EB, Builder.GetInsertBlock()))
+    return nullptr;
+
+  for (auto &PN : EB->phis()) {
+    if (!SE.isSCEVable(PN.getType()) || PN.getType() != S->getType())
+      continue;
+    auto *ExitV = SE.getSCEV(&PN);
+    if (S == ExitV)
+      return &PN;
+  }
+
+  return nullptr;
+}
+
 Value *SCEVExpander::visitAddRecExpr(const SCEVAddRecExpr *S) {
   // In canonical mode we compute the addrec as an expression of a canonical IV
   // using evaluateAtIteration and expand the resulting SCEV expression. This
@@ -1262,6 +1280,11 @@ Value *SCEVExpander::visitAddRecExpr(const SCEVAddRecExpr *S) {
     return V;
   }
 
+  // If S is expanded outside the defining loop, check if there is a
+  // matching LCSSA phi node for it.
+  if (Value *V = tryToReuseLCSSAPhi(S))
+    return V;
+
   // {X,+,F} --> X + {0,+,F}
   if (!S->getStart()->isZero()) {
     if (isa<PointerType>(S->getType())) {