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<base href="https://llvm.org/bugs/" />
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<body><table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW " title="NEW --- - [wrong code] _mm_alignr_epi8 is transformed to an incorrect shift" href="https://urldefense.proofpoint.com/v2/url?u=https-3A__llvm.org_bugs_show-5Fbug.cgi-3Fid-3D24187&d=AwMBaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=pF93YEPyB-J_PERP4DUZOJDzFVX5ZQ57vQk33wu0vio&m=ONbzg9-bQ_zcmcPTir-DJRVxbquHGqvR8w4qqrQMNCw&s=oxrf3JMYxga8wW7dqo7Prc7ll_YRddHpBmvHEbR3P9w&e=">24187</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>[wrong code] _mm_alignr_epi8 is transformed to an incorrect shift
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
<tr>
<th>Version</th>
<td>3.7
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
<tr>
<th>OS</th>
<td>Linux
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>-New Bugs
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>kretz@kde.org
</td>
</tr>
<tr>
<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
</td>
</tr>
<tr>
<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>Consider the following program:
#include <cstdio>
#include <x86intrin.h>
void print(__m128i a)
{
alignas(16) int m[4];
_mm_store_si128(reinterpret_cast<__m128i*>(m), a);
std::printf("[%d %d %d %d]\n", m[0], m[1], m[2], m[3]);
}
int main()
{
__m128i lo = _mm_setr_epi32(0, 1, 2, 3);
__m128i hi = _mm_setr_epi32(4, 5, 6, 7);
print(_mm_alignr_epi8(hi, lo, 0 * 4));
print(_mm_alignr_epi8(hi, lo, 1 * 4));
print(_mm_alignr_epi8(hi, lo, 2 * 4));
print(_mm_alignr_epi8(hi, lo, 3 * 4));
print(_mm_alignr_epi8(hi, lo, 4 * 4));
print(_mm_alignr_epi8(hi, lo, 5 * 4));
print(_mm_alignr_epi8(hi, lo, 6 * 4));
print(_mm_alignr_epi8(hi, lo, 7 * 4));
print(_mm_alignr_epi8(hi, lo, 8 * 4));
return 0;
}
It prints:
[0 1 2 3]
[1 2 3 4]
[2 3 4 5]
[3 4 5 6]
[4 5 6 7]
[1 2 3 0]
[2 3 0 0]
[3 0 0 0]
[0 0 0 0]
It should print:
[0 1 2 3]
[1 2 3 4]
[2 3 4 5]
[3 4 5 6]
[4 5 6 7]
[5 6 7 0]
[6 7 0 0]
[7 0 0 0]
[0 0 0 0]
Reduced testcase:
#include <tmmintrin.h>
int main()
{
alignas(16) int m[4];
*reinterpret_cast<__m128i*>(m) = _mm_alignr_epi8((__v4si{4, 5, 6, 7}),
(__v4si{0, 1, 2, 3}), 20);
if (m[0] != 5) {
abort();
}
return 0;
}</pre>
</div>
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