[PATCH] D146999: [LV][NFC] Improve complexity of fixing users of recurrences

[Michael Maitland via Phabricator via llvm-commits]

michaelmaitland created this revision.
michaelmaitland added reviewers: ABataev, fhahn, reames.
Herald added subscribers: StephenFan, hiraditya.
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michaelmaitland requested review of this revision.
Herald added subscribers: llvm-commits, pcwang-thead.
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The original loop has 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).


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D146999

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
@@ -3890,12 +3890,16 @@
   // had multiple exiting edges (as we always run the last iteration in the
   // scalar epilogue); in that case, there is no edge from middle to exit and
   // and thus no phis which needed updated.
-  if (!Cost->requiresScalarEpilogue(VF))
-    for (PHINode &LCSSAPhi : LoopExitBlock->phis())
-      if (llvm::is_contained(LCSSAPhi.incoming_values(), Phi)) {
-        LCSSAPhi.addIncoming(ExtractForPhiUsedOutsideLoop, LoopMiddleBlock);
-        State.Plan->removeLiveOut(&LCSSAPhi);
-      }
+  if (!Cost->requiresScalarEpilogue(VF)) {
+    llvm::SmallPtrSet<PHINode *, 2> ToFix;
+    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(ExtractForPhiUsedOutsideLoop, LoopMiddleBlock);
+      State.Plan->removeLiveOut(LCSSAPhi);
+    }
+  }
 }
 
 void InnerLoopVectorizer::fixReduction(VPReductionPHIRecipe *PhiR,


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