[PATCH] D45374: [LoopUnroll] Limit peeling to conds in BBs executed on every iteration.

[Florian Hahn via Phabricator via llvm-commits]

fhahn added a comment.

Thanks for having a look and sorry for not being clearer. Chad discovered a regression in SPEC2006's h264ref with LTO, caused by this change. The problem was that we peeled off an iteration of a big loop before LTO. That caused the function to be too big for the inliner during LTO, whereas it would be inlined before. We based the peeling decision on a nested condition. With this patch I tried to find a balance between increasing code size and benefits of peeling (simplifying nested conditionals are likely to have less positive impact than top-level ones).

@mcrosier did some more digging and found that we might just want to run simple unrolling before LTO and normal unrolling/peeling during LTO, which makes a sense to me. With that, we would not need this patch (or we could only consider top-level conditionals for "simple" peeling) and IMO that is what we should try to do.


https://reviews.llvm.org/D45374