1 files changed, 5 insertions, 0 deletions
diff --git a/lib/Transforms/Scalar/LoopStrengthReduce.cpp b/lib/Transforms/Scalar/LoopStrengthReduce.cpp
index 5bbc8322bc..83bdb2cd17 100644
--- a/lib/Transforms/Scalar/LoopStrengthReduce.cpp
+++ b/lib/Transforms/Scalar/LoopStrengthReduce.cpp
@@ -1823,6 +1823,7 @@ bool LoopStrengthReduce::runOnLoop(Loop *L, LPPassManager &LPM) {
       // FIXME: this needs to eliminate an induction variable even if it's being
       // compared against some value to decide loop termination.
       if (PN->hasOneUse()) {
+        SmallPtrSet<PHINode *, 2> PHIs;
         for (Instruction *J = dyn_cast<Instruction>(*PN->use_begin());
              J && J->hasOneUse() && !J->mayWriteToMemory();
              J = dyn_cast<Instruction>(*J->use_begin())) {
@@ -1835,6 +1836,10 @@ bool LoopStrengthReduce::runOnLoop(Loop *L, LPPassManager &LPM) {
             Changed = true;
             break;
           }
+          // If we find a PHI more than once, we're on a cycle that
+          // won't prove fruitful.
+          if (isa<PHINode>(J) && !PHIs.insert(cast<PHINode>(J)))
+            break;
         }
       }
     }