[PATCH] D88819: [LV] Support for Remainder loop vectorization

[Bardia Mahjour via Phabricator via llvm-commits]

bmahjour added a comment.

I also agree with @mivnay's summary above and the general approach of just running ILV again on the remainder loop with the available vplan. If we mark the epilogue loop and put it back in the worklist, it'll be harder/uglier to then modify the CFG to make it more optimal. I do, however, think that the implementation can be improved (see my note below). Please also note that the SCEV and runtime checks **cannot **be avoided by marking them "noalias" (or similar tricks) because if the iteration count of the loop is small enough to by-pass the main vector loop and large enough to execute the vector epilogue, then the runtime checks need to be executed for the epilogue loop. The only way to avoid the redundant runtime checks is to generate the smaller trip count check first, as illustrated in the CFG I've posted above.

I have an alternative implementation with the same general approach, but with a bit more modular design that also avoids the extra runtime checks using the mentioned CFG. I've cleaned it up a little but haven't had time to post a patch. I should have it ready by the end of the week.


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