[PATCH] D78630: [LV] Clamp the Unroll Factor to at least 1

[Simon Moll via Phabricator via llvm-commits]

simoll created this revision.
simoll added reviewers: fhahn, hsaito, Ayal, mkuper.
Herald added subscribers: llvm-commits, rkruppe, hiraditya.
Herald added a project: LLVM.

LV requires the unroll factor (UF) to be >= 1. This patch adds an explicit assertion for this and fixes a case in the cost model where the UF was set to zero. This was exposed by an out-of-tree TTI implementation that reported zero scores for candidate vectorization factors.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D78630

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
@@ -5300,7 +5300,8 @@
   // If trip count is known or estimated compile time constant, limit the
   // interleave count to be less than the trip count divided by VF.
   if (BestKnownTC) {
-    MaxInterleaveCount = std::min(*BestKnownTC / VF, MaxInterleaveCount);
+    MaxInterleaveCount =
+        std::max(1u, std::min(*BestKnownTC / VF, MaxInterleaveCount));
   }
 
   // If we did not calculate the cost for VF (because the user selected the VF)
@@ -5321,6 +5322,7 @@
   // benefit from interleaving.
   if (VF > 1 && !Legal->getReductionVars().empty()) {
     LLVM_DEBUG(dbgs() << "LV: Interleaving because of reductions.\n");
+    assert(IC > 0);
     return IC;
   }
 


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