[LoopRotate] Don't perform loop rotation if the loop header calls a convergent function.

Summary:
Calls to convergent functions can be duplicated, but only if the
duplicates are not control-flow dependent on any additional values.
Loop rotation doesn't meet the bar.

Reviewers: jingyue

Subscribers: mzolotukhin, llvm-commits, arsenm, joker.eph, resistor, tra, hfinkel, broune

Differential Revision: http://reviews.llvm.org/D17127

llvm-svn: 260729

1 files changed, 5 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/Scalar/LoopRotation.cpp b/llvm/lib/Transforms/Scalar/LoopRotation.cpp
index 5e6c2da08cc..14621e51b60 100644
--- a/llvm/lib/Transforms/Scalar/LoopRotation.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopRotation.cpp
@@ -165,6 +165,11 @@ static bool rotateLoop(Loop *L, unsigned MaxHeaderSize, LoopInfo *LI,
             << " instructions: "; L->dump());
       return false;
     }
+    if (Metrics.convergent) {
+      DEBUG(dbgs() << "LoopRotation: NOT rotating - contains convergent "
+                      "instructions: "; L->dump());
+      return false;
+    }
     if (Metrics.NumInsts > MaxHeaderSize)
       return false;
   }