[PATCH] D68082: [LV] Emitting SCEV checks with OptForSize

[Ayal Zaks via Phabricator via llvm-commits]

Ayal added a comment.

> At this point, PSE.getUnionPredicate().getPredicates() returns 0

Can you track where/when the predicate is generated and added to PSE?

The original bailout in `LoopVectorizationLegality::canVectorize()` checking `if (PSE.getUnionPredicate().getComplexity() > SCEVThreshold)` could potentially be extended - essentially zeroing SCEVThreshold for hasOptSize, but this takes place *earlier* than runtimeChecksRequired() which is claimed to be too early, contrary to the following claim:

  // Okay! We've done all the tests. If any have failed, return false. Otherwise
  // we can vectorize, and at this point we don't have any other mem analysis
  // which may limit our maximum vectorization factor, so just return true with
  // no restrictions.

The latest bailout is probably `LoopVectorizationCostModel::selectVectorizationFactor()`, but it's better to bailout earlier.

BTW, a related opportunity is `// FIXME: Avoid specializing for stride==1 instead of bailing out.`


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  https://reviews.llvm.org/D68082/new/

https://reviews.llvm.org/D68082