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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - __m64 not passed according to x86-64 ABI"
href="https://llvm.org/bugs/show_bug.cgi?id=26832">26832</a>
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<th>Summary</th>
<td>__m64 not passed according to x86-64 ABI
</td>
</tr>
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<th>Product</th>
<td>clang
</td>
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<th>Version</th>
<td>unspecified
</td>
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<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>Linux
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>-New Bugs
</td>
</tr>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>jyknight@google.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>Test program:
#include <mmintrin.h>
__m64 glob;
void xxxx(__m64 x) {
glob = x;
}
psABI says "Arguments of types float, double, _Decimal32, _Decimal64 and __m64
are in class SSE." That's pretty clear.
GCC, at least from 4.4.7 through 6 (the versions available at gcc.godbolt.org),
follows the psABI:
movq %xmm0, glob(%rip)
ret
Clang does not:
movq %rdi, glob(%rip)
retq
Clang claims it's doing so for gcc compatibility in a comment:
// gcc passes <1 x double> in memory. :(
// gcc passes <1 x long long> as INTEGER.
but that's not actually true (now; don't know about when the comment was
written)</pre>
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