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<body><span class="vcard"><a class="email" href="mailto:bruno.cardoso@gmail.com" title="Bruno Cardoso Lopes <bruno.cardoso@gmail.com>"> <span class="fn">Bruno Cardoso Lopes</span></a>
</span> changed
<a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED INVALID - Missed optimization by O2? LTO generates faster code than O2 with all code visible"
href="http://llvm.org/bugs/show_bug.cgi?id=21201">bug 21201</a>
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<th>What</th>
<th>Removed</th>
<th>Added</th>
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<td style="text-align:right;">Status</td>
<td>NEW
</td>
<td>RESOLVED
</td>
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<td style="text-align:right;">CC</td>
<td>
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<td>bruno.cardoso@gmail.com
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<td style="text-align:right;">Resolution</td>
<td>---
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<td>INVALID
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<b><a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED INVALID - Missed optimization by O2? LTO generates faster code than O2 with all code visible"
href="http://llvm.org/bugs/show_bug.cgi?id=21201#c2">Comment # 2</a>
on <a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED INVALID - Missed optimization by O2? LTO generates faster code than O2 with all code visible"
href="http://llvm.org/bugs/show_bug.cgi?id=21201">bug 21201</a>
from <span class="vcard"><a class="email" href="mailto:bruno.cardoso@gmail.com" title="Bruno Cardoso Lopes <bruno.cardoso@gmail.com>"> <span class="fn">Bruno Cardoso Lopes</span></a>
</span></b>
<pre>These are the results reproduced locally:
flags, random, in-order
tot-O2, 722.680343, 358.527025
tot-O2-flto, 586.257256, 113.567324
tot-O3, 763.348347, 340.556150
The only passes that run in LTO but do not run during non-LTO compilation are:
-argpromotion, -globalsmodref-aa, -internalize
The great responsible for the speedup is indeed -internalize, results bellow:
== llvm-lto flags, random, in-order
default, 551.342890, 107.292317
-nointernalize, 811.046609, 420.142491
-nointernalize-noglobalsmodref-aa, 779.453545, 412.112992
-nointernalize-noglobalsmodref-aa-noargsprom, 825.279406, 433.142810
Note that removing other passes yield the same results - the values above
all fall within the -nointernalize SD. With -internalize we're able to
delete 20 functions and inline 43, see the stats:
== llvm-lto
64 internalize - Number of functions internalized
50 internalize - Number of global vars internalized
150 inline - Number of caller-callers analyzed
20 inline - Number of functions deleted because all callers found
43 inline - Number of functions inlined
== llvm-lto without -internalize
no internalize results
no inline results
That said, nothing to do here anymore since -internalize only makes sense
during LTO.</pre>
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