[PATCH] D151658: [LV] Check if value was already not uniform for previous VF.

[Florian Hahn via Phabricator via llvm-commits]

fhahn created this revision.
fhahn added reviewers: Ayal, gilr, rengolin.
Herald added subscribers: StephenFan, javed.absar, hiraditya.
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If the value was already known to not be uniform for the previous
(smaller VF), it cannot be uniform for the larger VF.

This slightly reduces compile-time, once uniformity checks are becoming
a bit more expensive due to using SCEV rewriting (D148841 <https://reviews.llvm.org/D148841>).


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D151658

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
@@ -4671,9 +4671,17 @@
   if (Cmp && TheLoop->contains(Cmp) && Cmp->hasOneUse())
     addToWorklistIfAllowed(Cmp);
 
+  auto PrevVF = VF.divideCoefficientBy(2);
   // Return true if all lanes perform the same memory operation, and we can
   // thus chose to execute only one.
   auto isUniformMemOpUse = [&](Instruction *I) {
+    // If the value was already known to not be uniform for the previous
+    // (smaller VF), it cannot be uniform for the larger VF.
+    if (PrevVF.isVector()) {
+      auto Iter = Uniforms.find(PrevVF);
+      if (Iter != Uniforms.end() && !Iter->second.contains(I))
+        return false;
+    }
     if (!Legal->isUniformMemOp(*I))
       return false;
     if (isa<LoadInst>(I))


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