[PATCH] D33928: [LoopStrengthReduction] Treat SCEVUnknown pessimistically in LSR

[Wei Mi via Phabricator via llvm-commits]

wmi added a comment.

Hi Max,

The way you treat formula containing loop variant unknown as loser will definitely help for some cases. But I can also think of some cases that LSRUse with all-fixups-outside-loop may have no available formula after this filtering and LSR will end up doing nothing for the whole loop. This may cause regression. Think about a hypothetical loop with 10 different induction variables inside of loop. Ideally LSR can replace those 10 induction variables with a single one and will be very helpful for performance. If because a LSRUse with all-fixups-outside-loop has no available formula after filtering all the losers and LSR finds no solution for the loop, it will be a big lost.

Thanks,
Wei.


https://reviews.llvm.org/D33928