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<body><span class="vcard"><a class="email" href="mailto:douglas_yung@playstation.sony.com" title="Douglas Yung <douglas_yung@playstation.sony.com>"> <span class="fn">Douglas Yung</span></a>
</span> changed
<a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED INVALID - Result of __builtin_ctzs() and __tzcnt_u16() not matching after 2af95a52"
href="https://bugs.llvm.org/show_bug.cgi?id=50569">bug 50569</a>
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<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>
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<tr>
<td style="text-align:right;">Resolution</td>
<td>---
</td>
<td>INVALID
</td>
</tr></table>
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<b><a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED INVALID - Result of __builtin_ctzs() and __tzcnt_u16() not matching after 2af95a52"
href="https://bugs.llvm.org/show_bug.cgi?id=50569#c2">Comment # 2</a>
on <a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED INVALID - Result of __builtin_ctzs() and __tzcnt_u16() not matching after 2af95a52"
href="https://bugs.llvm.org/show_bug.cgi?id=50569">bug 50569</a>
from <span class="vcard"><a class="email" href="mailto:douglas_yung@playstation.sony.com" title="Douglas Yung <douglas_yung@playstation.sony.com>"> <span class="fn">Douglas Yung</span></a>
</span></b>
<pre>I think you are correct that the test has been passing 0 to tzcnt which results
in undefined behavior and that we were previously just getting lucky.
In investigating this issue before I reported it, I wrote a small program that
performed the actions the test was taking and compared the result for all
values of short from the min to the max and only 0 showed an issue. I then
added some code to dump out the value that was being passed to the intrinsic
and it seemed to be consistently be 0. I suspect that our convoluted
initialization using a union with doubles/shorts (int -> double -> short via
union) was always getting 0 causing the issue.
I'm going to resolve this as invalid and update our internal test to detect
when we are attempting to pass 0 to the intrinsic and select a different value
to avoid the undefined behavior.
Thanks for the help!</pre>
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