1 files changed, 9 insertions, 3 deletions

diff --git a/contrib/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp b/contrib/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
index da3ac06ab464..554944404708 100644
--- a/contrib/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
+++ b/contrib/llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp
@@ -4146,8 +4146,8 @@ bool SLPVectorizerPass::tryToVectorizeList(ArrayRef<Value *> VL, BoUpSLP &R,
       if (AllowReorder && R.shouldReorder()) {
         // Conceptually, there is nothing actually preventing us from trying to
         // reorder a larger list. In fact, we do exactly this when vectorizing
-        // reductions. However, at this point, we only expect to get here from
-        // tryToVectorizePair().
+        // reductions. However, at this point, we only expect to get here when
+        // there are exactly two operations.
         assert(Ops.size() == 2);
         assert(BuildVectorSlice.empty());
         Value *ReorderedOps[] = {Ops[1], Ops[0]};
@@ -4904,7 +4904,13 @@ bool SLPVectorizerPass::vectorizeChainsInBlock(BasicBlock *BB, BoUpSLP &R) {
       // Try to vectorize them.
       unsigned NumElts = (SameTypeIt - IncIt);
       DEBUG(errs() << "SLP: Trying to vectorize starting at PHIs (" << NumElts << ")\n");
-      if (NumElts > 1 && tryToVectorizeList(makeArrayRef(IncIt, NumElts), R)) {
+      // The order in which the phi nodes appear in the program does not matter.
+      // So allow tryToVectorizeList to reorder them if it is beneficial. This
+      // is done when there are exactly two elements since tryToVectorizeList
+      // asserts that there are only two values when AllowReorder is true.
+      bool AllowReorder = NumElts == 2;
+      if (NumElts > 1 && tryToVectorizeList(makeArrayRef(IncIt, NumElts), R,
+                                            None, AllowReorder)) {
         // Success start over because instructions might have been changed.
         HaveVectorizedPhiNodes = true;
         Changed = true;