[PATCH] D76838: [LV][LoopInfo] Transform counting-down loops to counting-up loop

[Ayal Zaks via Phabricator via llvm-commits]

Ayal added inline comments.


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Comment at: llvm/include/llvm/Analysis/LoopInfo.h:580
   /// The IndVarSimplify pass transforms loops to have a canonical induction
   /// variable.
   ///
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Following the above comment, this Analysis should rely on a previous Transformation to produce a canonical induction variable, if needed.

If this transformation is applied to a loop before deciding to vectorize it, there may be potential slowdowns when the loop remains unvectorized; so best handled independent of LV.

In terms of implementation, as far as LV is concerned, if getCanonicalInductionVariable() fails and one is to be constructed, do so by relying on  SCEV::getBackedgeTakenCount() instead of pattern matching.

Cf. http://lists.llvm.org/pipermail/llvm-dev/2020-March/140433.html


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  https://reviews.llvm.org/D76838/new/

https://reviews.llvm.org/D76838