[PATCH] D102982: [LoopUnroll] Use smallest exact trip count from any exit

[Nikita Popov via Phabricator via llvm-commits]

nikic added a comment.

@reames Thanks for the patient explanation and me being so dense. No idea what I was thinking here.

To loop back around to the unrolling use-case, D103182 <https://reviews.llvm.org/D103182> would now provide us with an exact trip count for the loop. However, I think we still need to use the approach from this patch, or something similar to it, for two reasons:

- Without the knowledge //which// exit the trip count is for, we can fold all exits before the TripCount to "not taken", but we don't know which exit is the taken one on the last iteration.
- For trip multiples, the "loop trip multiple" would be the minimum of all trip multiples (please correct me if I'm wrong on that!) which I believe is not what is desired for unrolling. If we have one unpredictable exit and one multiple-4 exit, we'd want to unroll against that exit and save use the intermediate branches, but the "loop trip multiple" would be 1 in that case, as we can exit from the loop on every iteration.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D102982/new/

https://reviews.llvm.org/D102982