[PATCH] D133017: [LV] Use SCEV to check if the trip count <= VF * UF.

[Ayal Zaks via Phabricator via llvm-commits]

Ayal accepted this revision.
Ayal added a comment.
This revision is now accepted and ready to land.

Looks good to me, thanks.



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Comment at: llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp:483
       Plan.getCanonicalIV()->getStartValue()->getLiveInIRValue()->getType();
   const SCEV *ExitCount = createTripCountSCEV(IdxTy, PSE);
   ScalarEvolution &SE = *PSE.getSE();
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Thought: create vector trip count SCEV, once VF and UF are set; use it to create vector trip count Value, and also to check if it is known to be less than or equal to 1?


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Comment at: llvm/lib/Transforms/Vectorize/VPlanTransforms.cpp:469
+  if (ExitCount->isZero() ||
+      !SE.isKnownPredicate(CmpInst::ICMP_ULE, ExitCount, C))
     return;
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fhahn wrote:
> Ayal wrote:
> > Could this be simplified using SE.getSmallConstantMaxTripCount(L)? Or a caching thereof.
> `SE.getSmallConstantMaxTripCount(L)` only supports the case where the trip count is a constant, while `isKnownPredicate` supports the non-constant case as well.
Ok. Non-constant case seems a bit extreme, unless tail is folded - vectorizing and unrolling to a known upper bound will otherwise run the original scalar loop whenever its trip count misses the exact upper bound.


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  https://reviews.llvm.org/D133017/new/

https://reviews.llvm.org/D133017