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<body><span class="vcard"><a class="email" href="mailto:cycheng@multicorewareinc.com" title="cycheng <cycheng@multicorewareinc.com>"> <span class="fn">cycheng</span></a>
</span> changed
<a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED FIXED - [ppc] bad code layout causes slower than gcc in 403.gcc"
href="https://llvm.org/bugs/show_bug.cgi?id=25782">bug 25782</a>
<br>
<table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>What</th>
<th>Removed</th>
<th>Added</th>
</tr>
<tr>
<td style="text-align:right;">Status</td>
<td>ASSIGNED
</td>
<td>RESOLVED
</td>
</tr>
<tr>
<td style="text-align:right;">Resolution</td>
<td>---
</td>
<td>FIXED
</td>
</tr></table>
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<div>
<b><a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED FIXED - [ppc] bad code layout causes slower than gcc in 403.gcc"
href="https://llvm.org/bugs/show_bug.cgi?id=25782#c2">Comment # 2</a>
on <a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED FIXED - [ppc] bad code layout causes slower than gcc in 403.gcc"
href="https://llvm.org/bugs/show_bug.cgi?id=25782">bug 25782</a>
from <span class="vcard"><a class="email" href="mailto:cycheng@multicorewareinc.com" title="cycheng <cycheng@multicorewareinc.com>"> <span class="fn">cycheng</span></a>
</span></b>
<pre>Hi Carrot,
Current Machine Block Placement provides a mechanism called "Precise (Loop)
Rotation Cost", it's aimed at this issue, and you can enable it by:
-mllvm -force-precise-rotation-cost=true (after r269267)
Performance data is available here:
(base compile option = -m64 -O3 -mcpu=power8)
<a href="http://reviews.llvm.org/D20017#428394">http://reviews.llvm.org/D20017#428394</a>
403.gcc got improved a lot.
davidxl plans to enable it by default.
I still saw an optimization opportunity, because his current mechanism will
bypass this pattern:
entry
|
------> loop.header (body)
|97% / \
| /50% \50%
--- latch <--- if.then
|
|3%
loop.end
And I found libquantum, h264ref can get benefit if we rotate loop top for this
pattern.
Anyway, your issue of 403.gcc is solved by "-force-precise-rotation-cost".
CY</pre>
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