[PATCH] D84108: [SimplifyCFG][LoopRotate] SimplifyCFG: disable common instruction hoisting by default, enable late in pipeline

[Florian Hahn via Phabricator via llvm-commits]

fhahn added a comment.

In D84108#2481728 <https://reviews.llvm.org/D84108#2481728>, @sanwou01 wrote:

> In D84108#2422611 <https://reviews.llvm.org/D84108#2422611>, @fhahn wrote:
>
>> I had a first look and it seems like there's some bad interactions with the LTO pipeline. The problem in this case is the following: we now rotate a loop just before the vectorizer which requires duplicating a function call in the preheader when compiling the individual files. But this then stops inlining during LTO. I'll look into whether we should avoid rotating such loops in the 'prepare-for-lto' stage.
>
> Hi Florian, did you get anywhere with this? If I understand correctly, generally, the verctorizer wants to see the loops in rotated form, so trying to avoid rotations in certain cases might not be the right approach? At the same time, I'm not sure what else we could do! Any thoughts appreciated, and, if this has slipped down your priorities I'm happy to pick this up. It's been bumped up on my list!

I put up D94232 <https://reviews.llvm.org/D94232> with the approach I outlined earlier. I tried to summarize why I think this should make sense in the description. It would be great if you could give it a try on a set of benchmarks.


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