LSR critical edge splitting fix for PR13756.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@164147 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 15 insertions, 11 deletions

diff --git a/lib/Transforms/Scalar/LoopStrengthReduce.cpp b/lib/Transforms/Scalar/LoopStrengthReduce.cpp
index bcd27b132f..1d3d156887 100644
--- a/lib/Transforms/Scalar/LoopStrengthReduce.cpp
+++ b/lib/Transforms/Scalar/LoopStrengthReduce.cpp
@@ -4464,17 +4464,21 @@ void LSRInstance::RewriteForPHI(PHINode *PN,
             SplitLandingPadPredecessors(Parent, BB, "", "", P, NewBBs);
             NewBB = NewBBs[0];
           }
-
-          // If PN is outside of the loop and BB is in the loop, we want to
-          // move the block to be immediately before the PHI block, not
-          // immediately after BB.
-          if (L->contains(BB) && !L->contains(PN))
-            NewBB->moveBefore(PN->getParent());
-
-          // Splitting the edge can reduce the number of PHI entries we have.
-          e = PN->getNumIncomingValues();
-          BB = NewBB;
-          i = PN->getBasicBlockIndex(BB);
+          // If NewBB==NULL, then SplitCriticalEdge refused to split because all
+          // phi predecessors are identical. The simple thing to do is skip
+          // splitting in this case rather than complicate the API.
+          if (NewBB) {
+            // If PN is outside of the loop and BB is in the loop, we want to
+            // move the block to be immediately before the PHI block, not
+            // immediately after BB.
+            if (L->contains(BB) && !L->contains(PN))
+              NewBB->moveBefore(PN->getParent());
+
+            // Splitting the edge can reduce the number of PHI entries we have.
+            e = PN->getNumIncomingValues();
+            BB = NewBB;
+            i = PN->getBasicBlockIndex(BB);
+          }
         }
       }