[PATCH] D103026: [LoopUnroll] Explicitly specify exit to unroll against (NFCI)

[Philip Reames via Phabricator via llvm-commits]

reames added a comment.

Not sure if this would work or not, but if the implementation allows, I might suggest computing the symbolic exit count for each loop upfront (before unrolling starts).  Once you have that, there's a couple of cases:

- If Exit EC > UC, branch folds to untaken.
- If Exit EC == UC, then branch folds to untaken on all but one iteration, and taken on that iteration.
- If Exit EC < UC, we can clamp the UC.

Doing this as symbolic comparisons in the unroll implementation (as opposed to passing in a flag) seems likely to be more robust.


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https://reviews.llvm.org/D103026