[LoopInterchange] Only skip PHIs with incoming values from the inner loop.

Currently we have limited support for outer loops with multiple basic
blocks after the inner loop exit. But the current checks for creating
PHIs for loop exit values only assumes the header and latches of the
outer loop. It is better to just skip incoming values defined in the
original inner loops. Those are handled earlier.

Reviewers: efriedma, mcrosier

Reviewed By: efriedma

Differential Revision: https://reviews.llvm.org/D70059

1 files changed, 7 insertions, 7 deletions

diff --git a/llvm/lib/Transforms/Scalar/LoopInterchange.cpp b/llvm/lib/Transforms/Scalar/LoopInterchange.cpp
index 1af4b21b432..4149995480f 100644
--- a/llvm/lib/Transforms/Scalar/LoopInterchange.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopInterchange.cpp
@@ -1339,7 +1339,8 @@ static void updateSuccessor(BranchInst *BI, BasicBlock *OldBB,
 // Move Lcssa PHIs to the right place.
 static void moveLCSSAPhis(BasicBlock *InnerExit, BasicBlock *InnerHeader,
                           BasicBlock *InnerLatch, BasicBlock *OuterHeader,
-                          BasicBlock *OuterLatch, BasicBlock *OuterExit) {
+                          BasicBlock *OuterLatch, BasicBlock *OuterExit,
+                          Loop *InnerLoop, LoopInfo *LI) {
 
   // Deal with LCSSA PHI nodes in the exit block of the inner loop, that are
   // defined either in the header or latch. Those blocks will become header and
@@ -1394,19 +1395,17 @@ static void moveLCSSAPhis(BasicBlock *InnerExit, BasicBlock *InnerHeader,
     P->moveBefore(InnerExit->getFirstNonPHI());
 
   // Deal with LCSSA PHI nodes in the loop nest exit block. For PHIs that have
-  // incoming values from the outer latch or header, we have to add a new PHI
+  // incoming values defined in the outer loop, we have to add a new PHI
   // in the inner loop latch, which became the exit block of the outer loop,
   // after interchanging.
   if (OuterExit) {
     for (PHINode &P : OuterExit->phis()) {
       if (P.getNumIncomingValues() != 1)
         continue;
-      // Skip Phis with incoming values not defined in the outer loop's header
-      // and latch. Also skip incoming phis defined in the latch. Those should
+      // Skip Phis with incoming values defined in the inner loop. Those should
       // already have been updated.
       auto I = dyn_cast<Instruction>(P.getIncomingValue(0));
-      if (!I || ((I->getParent() != OuterLatch || isa<PHINode>(I)) &&
-                 I->getParent() != OuterHeader))
+      if (!I || LI->getLoopFor(I->getParent()) == InnerLoop)
         continue;
 
       PHINode *NewPhi = dyn_cast<PHINode>(P.clone());
@@ -1520,7 +1519,8 @@ bool LoopInterchangeTransform::adjustLoopBranches() {
                    OuterLoopPreHeader);
 
   moveLCSSAPhis(InnerLoopLatchSuccessor, InnerLoopHeader, InnerLoopLatch,
-                OuterLoopHeader, OuterLoopLatch, InnerLoop->getExitBlock());
+                OuterLoopHeader, OuterLoopLatch, InnerLoop->getExitBlock(),
+                InnerLoop, LI);
   // For PHIs in the exit block of the outer loop, outer's latch has been
   // replaced by Inners'.
   OuterLoopLatchSuccessor->replacePhiUsesWith(OuterLoopLatch, InnerLoopLatch);