Don't split any loop backedges, including backedges of loops other than

the active loop. This is generally desirable, and it avoids trouble
in situations such as the testcase in PR9123, though the failure
mode depends on use-list order, so it is infeasible to test.

llvm-svn: 125065

1 files changed, 17 insertions, 15 deletions

diff --git a/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp b/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
index d431b6815c4..01dcfaf0652 100644
--- a/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopStrengthReduce.cpp
@@ -3544,21 +3544,23 @@ void LSRInstance::RewriteForPHI(PHINode *PN,
       // is the canonical backedge for this loop, which complicates post-inc
       // users.
       if (e != 1 && BB->getTerminator()->getNumSuccessors() > 1 &&
-          !isa<IndirectBrInst>(BB->getTerminator()) &&
-          (PN->getParent() != L->getHeader() || !L->contains(BB))) {
-        // Split the critical edge.
-        BasicBlock *NewBB = SplitCriticalEdge(BB, PN->getParent(), P);
-
-        // 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);
+          !isa<IndirectBrInst>(BB->getTerminator())) {
+        Loop *PNLoop = LI.getLoopFor(PN->getParent());
+        if (!PNLoop || PN->getParent() != PNLoop->getHeader()) {
+          // Split the critical edge.
+          BasicBlock *NewBB = SplitCriticalEdge(BB, PN->getParent(), P);
+
+          // 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);
+        }
       }
 
       std::pair<DenseMap<BasicBlock *, Value *>::iterator, bool> Pair =