Avoid spliting loops where two split condition branches are not independent.

llvm-svn: 41148

1 files changed, 11 insertions, 1 deletions

diff --git a/llvm/lib/Transforms/Scalar/LoopIndexSplit.cpp b/llvm/lib/Transforms/Scalar/LoopIndexSplit.cpp
index 980990ea652..9b4319d40cd 100644
--- a/llvm/lib/Transforms/Scalar/LoopIndexSplit.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopIndexSplit.cpp
@@ -711,12 +711,22 @@ bool LoopIndexSplit::splitLoop(SplitInfo &SD) {
           || Latch == SplitTerminator->getSuccessor(1)))
     return false;
 
-
+  // If one of the split condition branch is post dominating other then loop 
+  // index split is not appropriate.
   BasicBlock *Succ0 = SplitTerminator->getSuccessor(0);
   BasicBlock *Succ1 = SplitTerminator->getSuccessor(1);
   if (DT->dominates(Succ0, Latch) || DT->dominates(Succ1, Latch))
     return false;
 
+  // If one of the split condition branch is a predecessor of the other
+  // split condition branch head then do not split loop on this condition.
+  for(pred_iterator PI = pred_begin(Succ0), PE = pred_end(Succ0); PI != PE; ++PI)
+    if (Succ1 == *PI)
+      return false;
+  for(pred_iterator PI = pred_begin(Succ1), PE = pred_end(Succ1); PI != PE; ++PI)
+    if (Succ0 == *PI)
+      return false;
+
   // True loop is original loop. False loop is cloned loop.
 
   bool SignedPredicate = ExitCondition->isSignedPredicate();