1 files changed, 17 insertions, 1 deletions
diff --git a/llvm/lib/Transforms/Utils/LoopUnroll.cpp b/llvm/lib/Transforms/Utils/LoopUnroll.cpp
index f070c7f..fb98b30 100644
--- a/llvm/lib/Transforms/Utils/LoopUnroll.cpp
+++ b/llvm/lib/Transforms/Utils/LoopUnroll.cpp
@@ -273,7 +273,23 @@ bool llvm::UnrollLoop(Loop *L, unsigned Count, unsigned TripCount,
   // flag is specified.
   bool RuntimeTripCount = (TripCount == 0 && Count > 0 && AllowRuntime);
 
-  if (RuntimeTripCount &&
+  // Loops containing convergent instructions must have a count that divides
+  // their TripMultiple.
+  DEBUG(
+    bool HasConvergent = false;
+    for (auto &BB : L->blocks())
+      for (auto &I : *BB)
+        if (auto CS = CallSite(&I))
+          HasConvergent |= CS.isConvergent();
+    assert(
+        !HasConvergent || TripMultiple % Count == 0 &&
+        "Unroll count must divide trip multiple if loop contains a convergent "
+        "operation.");
+  );
+  // Don't output the runtime loop prolog if Count is a multiple of
+  // TripMultiple.  Such a prolog is never needed, and is unsafe if the loop
+  // contains a convergent instruction.
+  if (RuntimeTripCount && TripMultiple % Count != 0 &&
       !UnrollRuntimeLoopProlog(L, Count, AllowExpensiveTripCount, LI, SE, DT,
                                PreserveLCSSA))
     return false;