LSR should avoid redundant edge splitting.

This handles the case in which LSR rewrites an IV user that is a phi and
splits critical edges originating from a switch.
Fixes <rdar://problem/6453893> LSR is not splitting edges "nicely"


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@141059 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 6 insertions, 3 deletions

diff --git a/lib/Transforms/Scalar/LoopStrengthReduce.cpp b/lib/Transforms/Scalar/LoopStrengthReduce.cpp
index 7b1a340156..4b6c55e162 100644
--- a/lib/Transforms/Scalar/LoopStrengthReduce.cpp
+++ b/lib/Transforms/Scalar/LoopStrengthReduce.cpp
@@ -3677,7 +3677,9 @@ void LSRInstance::RewriteForPHI(PHINode *PN,
           // Split the critical edge.
           BasicBlock *NewBB = 0;
           if (!Parent->isLandingPad()) {
-            NewBB = SplitCriticalEdge(BB, Parent, P);
+            NewBB = SplitCriticalEdge(BB, Parent, P,
+                                      /*MergeIdenticalEdges=*/true,
+                                      /*DontDeleteUselessPhis=*/true);
           } else {
             SmallVector<BasicBlock*, 2> NewBBs;
             SplitLandingPadPredecessors(Parent, BB, "", "", P, NewBBs);
diff --git a/lib/Transforms/Utils/BreakCriticalEdges.cpp b/lib/Transforms/Utils/BreakCriticalEdges.cpp
index 4648f49645..c052910881 100644
--- a/lib/Transforms/Utils/BreakCriticalEdges.cpp
+++ b/lib/Transforms/Utils/BreakCriticalEdges.cpp
@@ -167,7 +167,8 @@ static void CreatePHIsForSplitLoopExit(SmallVectorImpl<BasicBlock *> &Preds,
 /// to.
 ///
 BasicBlock *llvm::SplitCriticalEdge(TerminatorInst *TI, unsigned SuccNum,
-                                    Pass *P, bool MergeIdenticalEdges) {
+                                    Pass *P, bool MergeIdenticalEdges,
+                                    bool DontDeleteUselessPhis) {
   if (!isCriticalEdge(TI, SuccNum, MergeIdenticalEdges)) return 0;
 
   assert(!isa<IndirectBrInst>(TI) &&
@@ -224,7 +225,7 @@ BasicBlock *llvm::SplitCriticalEdge(TerminatorInst *TI, unsigned SuccNum,
       if (TI->getSuccessor(i) != DestBB) continue;
 
       // Remove an entry for TIBB from DestBB phi nodes.
-      DestBB->removePredecessor(TIBB);
+      DestBB->removePredecessor(TIBB, DontDeleteUselessPhis);
 
       // We found another edge to DestBB, go to NewBB instead.
       TI->setSuccessor(i, NewBB);