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<div class="moz-cite-prefix">On 03/17/2017 04:30 PM, Mehdi Amini via
llvm-dev wrote:<br>
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<div class="">On Mar 17, 2017, at 11:50 AM, Mikhail Zolotukhin
via llvm-dev <<a moz-do-not-send="true"
href="mailto:llvm-dev@lists.llvm.org" class="">llvm-dev@lists.llvm.org</a>>
wrote:</div>
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<div class="">Hi,</div>
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<div class="">One of the most time-consuming passes
in LLVM middle-end is InstCombine (see e.g. [1]).
It is a very powerful pass capable of doing all
the crazy stuff, and new patterns are being
constantly introduced there. The problem is that
we often use it just as a clean-up pass: it's
scheduled 6 times in the current pass pipeline,
and each time it's invoked it checks all known
patterns. It sounds ok for O3, where we try to
squeeze as much performance as possible, but it is
too excessive for other opt-levels. InstCombine
has an ExpensiveCombines parameter to address that
- but I think it's underused at the moment.</div>
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<div>Yes, the “ExpensiveCombines” has been added recently (4.0?
3.9?) but I believe has always been intended to be extended
the way you’re doing it. So I support this effort :)</div>
</div>
</blockquote>
<br>
+1<br>
<br>
Also, did your profiling reveal why the other combines are
expensive? Among other things, I'm curious if the expensive ones
tend to spend a lot of time in ValueTracking (getting known bits and
similar)?<br>
<br>
-Hal<br>
<br>
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<div>CC: David for the general direction on InstCombine though.</div>
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</div>
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<div>— </div>
<div>Mehdi</div>
<div><br class="">
</div>
<div><br class="">
</div>
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<div class="">Trying to find out, which patterns are
important, and which are rare, I profiled clang
using CTMark and got the following coverage
report:</div>
</div>
</div>
</div>
</div>
<span
id="cid:CEA3012D-A9E2-4318-AA90-C372667C70A9@apple.com"><InstCombine_covreport.html></span>
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<div class="">(beware, the file is ~6MB).</div>
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</div>
<div class="">Guided by this profile I moved some
patterns under the "if (ExpensiveCombines)" check,
which expectedly happened to be neutral for
runtime performance, but improved compile-time.
The testing results are below (measured for Os).</div>
<div class=""><br class="">
</div>
<div class="">
<table class="" style="font-family: Helvetica,
sans-serif; font-size: 9pt; border-spacing: 0px;
border: 1px solid black;">
<thead class=""><tr class="">
<th style="background-color: rgb(238, 238,
238); color: rgb(102, 102, 102); cursor:
default; text-align: center; font-family:
Verdana; padding: 5px 5px 5px 8px; width:
500px;" class="">Performance Improvements
- Compile Time</th>
<th style="background-color: rgb(238, 238,
238); color: rgb(102, 102, 102); cursor:
default; text-align: center; font-family:
Verdana; padding: 5px 5px 5px 8px;"
class="">Δ </th>
<th style="background-color: rgb(238, 238,
238); color: rgb(102, 102, 102); cursor:
default; text-align: center; font-family:
Verdana; padding: 5px 5px 5px 8px;"
class="">Previous</th>
<th style="background-color: rgb(238, 238,
238); color: rgb(102, 102, 102); cursor:
default; text-align: center; font-family:
Verdana; padding: 5px 5px 5px 8px;"
class="">Current</th>
<th style="background-color: rgb(238, 238,
238); color: rgb(102, 102, 102); cursor:
default; text-align: center; font-family:
Verdana; padding: 5px 5px 5px 8px;"
class="">σ </th>
</tr>
</thead><tbody class="searchable">
<tr class="">
<td class="benchmark-name" style="padding:
5px 5px 5px 8px;"><a
moz-do-not-send="true"
href="http://michaelsmacmini.local/perf/v4/nts/2/graph?test.15=2"
class="">CTMark/sqlite3/sqlite3</a></td>
<td style="padding: 5px 5px 5px 8px;
background-color: rgb(200, 255, 200);"
class="">-1.55%</td>
<td style="padding: 5px 5px 5px 8px;"
class="">6.8155</td>
<td style="padding: 5px 5px 5px 8px;"
class="">6.7102</td>
<td style="padding: 5px 5px 5px 8px;"
class="">0.0081</td>
</tr>
<tr class="">
<td class="benchmark-name" style="padding:
5px 5px 5px 8px;"><a
moz-do-not-send="true"
href="http://michaelsmacmini.local/perf/v4/nts/2/graph?test.1=2"
class="">CTMark/mafft/pairlocalalign</a></td>
<td style="padding: 5px 5px 5px 8px;
background-color: rgb(209, 255, 209);"
class="">-1.05%</td>
<td style="padding: 5px 5px 5px 8px;"
class="">8.0407</td>
<td style="padding: 5px 5px 5px 8px;"
class="">7.9559</td>
<td style="padding: 5px 5px 5px 8px;"
class="">0.0193</td>
</tr>
<tr class="">
<td class="benchmark-name" style="padding:
5px 5px 5px 8px;"><a
moz-do-not-send="true"
href="http://michaelsmacmini.local/perf/v4/nts/2/graph?test.7=2"
class="">CTMark/ClamAV/clamscan</a></td>
<td style="padding: 5px 5px 5px 8px;
background-color: rgb(210, 255, 210);"
class="">-1.02%</td>
<td style="padding: 5px 5px 5px 8px;"
class="">11.3893</td>
<td style="padding: 5px 5px 5px 8px;"
class="">11.2734</td>
<td style="padding: 5px 5px 5px 8px;"
class="">0.0081</td>
</tr>
<tr class="">
<td class="benchmark-name" style="padding:
5px 5px 5px 8px;"><a
moz-do-not-send="true"
href="http://michaelsmacmini.local/perf/v4/nts/2/graph?test.10=2"
class="">CTMark/lencod/lencod</a></td>
<td style="padding: 5px 5px 5px 8px;
background-color: rgb(210, 255, 210);"
class="">-1.01%</td>
<td style="padding: 5px 5px 5px 8px;"
class="">12.8763</td>
<td style="padding: 5px 5px 5px 8px;"
class="">12.7461</td>
<td style="padding: 5px 5px 5px 8px;"
class="">0.0244</td>
</tr>
<tr class="">
<td class="benchmark-name" style="padding:
5px 5px 5px 8px;"><a
moz-do-not-send="true"
href="http://michaelsmacmini.local/perf/v4/nts/2/graph?test.5=2"
class="">CTMark/SPASS/SPASS</a></td>
<td style="padding: 5px 5px 5px 8px;
background-color: rgb(210, 255, 210);"
class="">-1.01%</td>
<td style="padding: 5px 5px 5px 8px;"
class="">12.5048</td>
<td style="padding: 5px 5px 5px 8px;"
class="">12.3791</td>
<td style="padding: 5px 5px 5px 8px;"
class="">0.0340</td>
</tr>
</tbody>
</table>
<div class=""><br class="">
</div>
<table class="" style="font-family: Helvetica,
sans-serif; font-size: 9pt; border-spacing: 0px;
border: 1px solid black;">
<thead class=""><tr class="">
<th style="background-color: rgb(238, 238,
238); color: rgb(102, 102, 102); cursor:
default; text-align: center; font-family:
Verdana; padding: 5px 5px 5px 8px; width:
500px;" class="">Performance Improvements
- Compile Time</th>
<th style="background-color: rgb(238, 238,
238); color: rgb(102, 102, 102); cursor:
default; text-align: center; font-family:
Verdana; padding: 5px 5px 5px 8px;"
class="">Δ </th>
<th style="background-color: rgb(238, 238,
238); color: rgb(102, 102, 102); cursor:
default; text-align: center; font-family:
Verdana; padding: 5px 5px 5px 8px;"
class="">Previous</th>
<th style="background-color: rgb(238, 238,
238); color: rgb(102, 102, 102); cursor:
default; text-align: center; font-family:
Verdana; padding: 5px 5px 5px 8px;"
class="">Current</th>
<th style="background-color: rgb(238, 238,
238); color: rgb(102, 102, 102); cursor:
default; text-align: center; font-family:
Verdana; padding: 5px 5px 5px 8px;"
class="">σ </th>
</tr>
</thead><tbody class="searchable">
<tr class="">
<td class="benchmark-name" style="padding:
5px 5px 5px 8px;"><a
moz-do-not-send="true"
href="http://michaelsmacmini.local/perf/v4/nts/2/graph?test.14=2"
class="">External/SPEC/CINT2006/403.gcc/403.gcc</a></td>
<td style="padding: 5px 5px 5px 8px;
background-color: rgb(199, 255, 199);"
class="">-1.64%</td>
<td style="padding: 5px 5px 5px 8px;"
class="">54.0801</td>
<td style="padding: 5px 5px 5px 8px;"
class="">53.1930</td>
<td style="padding: 5px 5px 5px 8px;"
class="">-</td>
</tr>
<tr class="">
<td class="benchmark-name" style="padding:
5px 5px 5px 8px;"><a
moz-do-not-send="true"
href="http://michaelsmacmini.local/perf/v4/nts/2/graph?test.7=2"
class="">External/SPEC/CINT2006/400.perlbench/400.perlbench</a></td>
<td style="padding: 5px 5px 5px 8px;
background-color: rgb(205, 255, 205);"
class="">-1.25%</td>
<td style="padding: 5px 5px 5px 8px;"
class="">19.1481</td>
<td style="padding: 5px 5px 5px 8px;"
class="">18.9091</td>
<td style="padding: 5px 5px 5px 8px;"
class="">-</td>
</tr>
<tr class="">
<td class="benchmark-name" style="padding:
5px 5px 5px 8px;"><a
moz-do-not-send="true"
href="http://michaelsmacmini.local/perf/v4/nts/2/graph?test.15=2"
class="">External/SPEC/CINT2006/445.gobmk/445.gobmk</a></td>
<td style="padding: 5px 5px 5px 8px;
background-color: rgb(210, 255, 210);"
class="">-1.01%</td>
<td style="padding: 5px 5px 5px 8px;"
class="">15.2819</td>
<td style="padding: 5px 5px 5px 8px;"
class="">15.1274</td>
<td style="padding: 5px 5px 5px 8px;"
class="">-</td>
</tr>
</tbody>
</table>
<div class=""><br class="">
</div>
<div class=""><br class="">
</div>
<div class="">Do such changes make sense? The
patch doesn't change O3, but it does change Os
and potentially can change performance there
(though I didn't see any changes in my tests).</div>
</div>
<div class=""><br class="">
</div>
<div class="">The patch is attached for the
reference, if we decide to go for it, I'll upload
it to phab:</div>
<div class=""><br class="">
</div>
</div>
</div>
</div>
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<span
id="cid:2A77C0D9-EE12-4C99-99A0-7A0CF5DF758A@apple.com"><0001-InstCombine-Move-some-infrequent-patterns-under-if-E.patch></span>
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<div class="">Thanks,</div>
<div class="">Michael</div>
<div class=""><br class="">
</div>
<div class="">
<div class="">[1]: <a moz-do-not-send="true"
href="http://lists.llvm.org/pipermail/llvm-dev/2016-December/108279.html"
class="">http://lists.llvm.org/pipermail/llvm-dev/2016-December/108279.html</a></div>
</div>
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<pre class="moz-signature" cols="72">--
Hal Finkel
Lead, Compiler Technology and Programming Languages
Leadership Computing Facility
Argonne National Laboratory</pre>
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