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<p>I know of no reason to have a strong preference. Assuming the
change wasn't made intentionally - might be good to check with
Chandler - I'd default to using the same order from the old pass
manager.</p>
<p>One argument in favor of the forward order is that if determine a
loop exit is dead, we might be able to avoid visiting a large
portion of the function. Just an observation, not an argument in
favor per se.</p>
<p>Philip<br>
</p>
<div class="moz-cite-prefix">On 4/15/21 9:59 AM, Arthur Eubanks via
llvm-dev wrote:<br>
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cite="mid:CAPW48srspHGNLr5QpaRzUdPqLCw4pRCbbWB69PR1_DkGXZQRGQ@mail.gmail.com">
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<div dir="ltr">Ping on loop traversal order. Does anybody have any
intuition about which way to traverse loops in a function?</div>
<br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Wed, Apr 7, 2021 at 12:36
PM Jingu Kang via llvm-dev <<a
href="mailto:llvm-dev@lists.llvm.org" moz-do-not-send="true">llvm-dev@lists.llvm.org</a>>
wrote:<br>
</div>
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0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
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<div class="gmail-m_3068285083701495126WordSection1">
<p class="MsoNormal">Hi All,</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal"><span
style="color:black;background:white">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
<a href="https://reviews.llvm.org/D99774"
target="_blank" moz-do-not-send="true">https://reviews.llvm.org/D99774</a>
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.</span><span
style="background:white"></span></p>
<p class="MsoNormal"><span style="background:white"> </span></p>
<p class="MsoNormal"><span
style="color:black;background:white">Thanks</span><span
style="background:white"></span></p>
<p class="MsoNormal"><span
style="color:black;background:white">JinGu Kang</span></p>
</div>
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