[llvm-dev] Question about Traversing Loops in forward or reverse program order on new pass manager

[Arthur Eubanks via llvm-dev]

Ping on loop traversal order. Does anybody have any intuition about which
way to traverse loops in a function?

On Wed, Apr 7, 2021 at 12:36 PM Jingu Kang via llvm-dev <
llvm-dev at lists.llvm.org> wrote:

> Hi All,
>
>
>
> I have seen performance regressions from new pass manager against legacy
> pass manager. One of the issues is the order of populating loops on pass
> manager. The legacy pass manager is traversing loops in reverse program
> order but the new pass manager is traversing in forward program order. It
> sometimes causes different output. I have created a review
> https://reviews.llvm.org/D99774 for reverse program order on new pass
> manager and had short discussion with Arthur on it. It is not easy to say
> the reverse order is better than the forward one or vice versa. I would
> like to share this issue with more people on llvm-dev. If you have idea or
> experience about this issue, please share it.
>
>
>
> Thanks
>
> JinGu Kang
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