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<body><span class="vcard"><a class="email" href="mailto:sebpop@gmail.com" title="Sebastian Pop <sebpop@gmail.com>"> <span class="fn">Sebastian Pop</span></a>
</span> changed
<a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED FIXED - Regression(r275401): assert while building ffmpeg"
href="https://llvm.org/bugs/show_bug.cgi?id=28551">bug 28551</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>NEW
</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 - Regression(r275401): assert while building ffmpeg"
href="https://llvm.org/bugs/show_bug.cgi?id=28551#c9">Comment # 9</a>
on <a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED FIXED - Regression(r275401): assert while building ffmpeg"
href="https://llvm.org/bugs/show_bug.cgi?id=28551">bug 28551</a>
from <span class="vcard"><a class="email" href="mailto:sebpop@gmail.com" title="Sebastian Pop <sebpop@gmail.com>"> <span class="fn">Sebastian Pop</span></a>
</span></b>
<pre>Which explains the crashes all over the place: the std::sort of today's libcxx
is inefficient as it calls the compare function on the same element:
// known that *(__i - 1) < *__m
// known that __i <= __m
while (true)
{
// __m still guards upward moving __i
while (__comp(*__i, *__m))
++__i;
// It is now known that a guard exists for downward moving __j
while (!__comp(*--__j, *__m))
;
if (__i > __j)
break;
swap(*__i, *__j);
++__n_swaps;
// It is known that __m != __j
// If __m just moved, follow it
if (__m == __i)
__m = __j;
++__i;
}
In particular this "if (__m == __i)" should be above the first call to
__comp().
Maybe some other places.
As the buildbots are not bootstrapping their libc++, there is not much I can do
to avoid all the users of Apple toolchains to see the assert failing.
I will remove the assert that I have in the GVNHoist code, and open a libcxx
bug for inefficiencies in the std::sort() algorithm.</pre>
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