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<base href="https://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - [SSE2] poor performance _mm_extract_epi8"
href="https://llvm.org/bugs/show_bug.cgi?id=27737">27737</a>
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<th>Summary</th>
<td>[SSE2] poor performance _mm_extract_epi8
</td>
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<th>Product</th>
<td>clang
</td>
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<th>Version</th>
<td>3.8
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>All
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Headers
</td>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>rozhuk.im@gmail.com
</td>
</tr>
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<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
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<th>Classification</th>
<td>Unclassified
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<p>
<div>
<pre>I have some code that heavy uses _mm_extract_epi8().
Then I build with clang 3.8 and -msse2 (without -msse4.1) then program work
very slow.
To build with GCC and clang 3.4, 3.6, 3.7 I use macro:
#ifndef _mm_extract_epi8 /* SSE4.1 required. */
#define _mm_extract_epi8(__xmm, __n) \
((_mm_extract_epi16(__xmm, ((__n) >> 1)) >> (8 * ((__n) & 1))) & 0xff)
#endif
Test results:
AMD Athlon(tm) 5350 APU with Radeon(tm) R3 (2050.04-MHz K8-class CPU)
GCC: 20391006000 (SSE4.1) / 20116413000 (SSE2)
clang 3.8: 22329895000 (SSE4.1) / 117304135000 (SSE2) !!!
clang 3.7: 22367008000 (SSE4.1) / 25542571000 (SSE2)
clang 3.6: 22306648000 (SSE4.1) / 25914115000 (SSE2)
clang 3.4: 23684031000 (SSE4.1) / 25914115000 (SSE2)
Intel(R) Core(TM)2 Duo CPU E8400 @ 3.00GHz (2999.72-MHz K8-class CPU)
GCC: 12031595000 (SSE4.1) / 12011303000 (SSE2)
clang 3.8: 12431116000 (SSE4.1) / 73035466000 (SSE2) !!!
clang 3.7: 12458839000 (SSE4.1) / 13317058000 (SSE2)
clang 3.6: 12462181000 (SSE4.1) / 14119683000 (SSE2)
clang 3.4: 13555167000 (SSE4.1) / 13178893000 (SSE2)</pre>
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