[PATCH] D147944: [LV][NFC] Improve complexity of fixing users of reductions

[Michael Maitland via Phabricator via llvm-commits]

michaelmaitland created this revision.
michaelmaitland added reviewers: fhahn, Ayal, ABataev.
Herald added subscribers: StephenFan, hiraditya.
Herald added a project: All.
michaelmaitland requested review of this revision.
Herald added subscribers: llvm-commits, pcwang-thead.
Herald added a project: LLVM.

The original loop is O(MxN) since is_contained iterates over
all incoming values. This change makes it so only the phis
which use the value as an incoming value are iterated over so
it is now O(M).

This patch is analogous to D146999 <https://reviews.llvm.org/D146999>.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D147944

Files:
  llvm/lib/Transforms/Vectorize/LoopVectorize.cpp


Index: llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
===================================================================
--- llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
+++ llvm/lib/Transforms/Vectorize/LoopVectorize.cpp
@@ -4100,12 +4100,17 @@
   // We know that the loop is in LCSSA form. We need to update the PHI nodes
   // in the exit blocks.  See comment on analogous loop in
   // fixFixedOrderRecurrence for a more complete explaination of the logic.
-  if (!Cost->requiresScalarEpilogue(VF))
-    for (PHINode &LCSSAPhi : LoopExitBlock->phis())
-      if (llvm::is_contained(LCSSAPhi.incoming_values(), LoopExitInst)) {
-        LCSSAPhi.addIncoming(ReducedPartRdx, LoopMiddleBlock);
-        State.Plan->removeLiveOut(&LCSSAPhi);
-      }
+  if (!Cost->requiresScalarEpilogue(VF)) {
+    SmallPtrSet<PHINode *, 2> ToFix;
+    PHINode *Phi = cast<PHINode>(PhiR->getUnderlyingValue());
+    for (User *U : Phi->users())
+      if (isa<PHINode>(U) && cast<Instruction>(U)->getParent() == LoopExitBlock)
+        ToFix.insert(cast<PHINode>(U));
+    for (PHINode *LCSSAPhi : ToFix) {
+      LCSSAPhi->addIncoming(ReducedPartRdx, LoopMiddleBlock);
+      State.Plan->removeLiveOut(LCSSAPhi);
+    }
+  }
 
   // Fix the scalar loop reduction variable with the incoming reduction sum
   // from the vector body and from the backedge value.


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D147944.512147.patch
Type: text/x-patch
Size: 1351 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20230410/97f81893/attachment.bin>