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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 --- - ABI incompatibilities between Clang and GCC (calling conventions for AVX512 vector arguments)"
href="https://llvm.org/bugs/show_bug.cgi?id=28975">28975</a>
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<th>Summary</th>
<td>ABI incompatibilities between Clang and GCC (calling conventions for AVX512 vector arguments)
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
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<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>All
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<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>Backend: X86
</td>
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<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>wenzel.jakob@epfl.ch
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
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</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>Consider the following simple program:
------------------------
#include <immintrin.h>
float test_float(float x) { return x; }
double test_double(double x) { return x; }
__m128 test_m128(__m128 x) { return x; }
__m256 test_m256(__m256 x) { return x; }
__m512 test_m512(__m512 x) { return x; }
------------------------
GCC trunk compiles this to the following optimized assembly (labels stripped
away for readability):
$ gcc test.c -O3 -Wall -Wabi -mavx512f -fomit-frame-pointer -o - -S
_test_f1:
ret
_test_f4:
ret
_test_f8:
ret
_test_f16:
ret
In other words, everything is passed via registers. On the other hand, clang
uses registers for everything *except* AVX512 SIMD registers:
$ clang test.c -O3 -Wall -Wabi -mavx512f -fomit-frame-pointer -o - -S
_test_f1:
retq
_test_f4:
retq
_test_f8:
retq
_test_f16:
pushq %rbp
movq %rsp, %rbp
andq $-64, %rsp
subq $64, %rsp
vmovaps 16(%rbp), %ymm0
vmovaps 48(%rbp), %ymm1
vmovaps %ymm1, 32(%rdi)
vmovaps %ymm0, (%rdi)
movq %rdi, %rax
movq %rbp, %rsp
popq %rbp
retq
It would be desirable if Clang would match GCC's behavior here.</pre>
</div>
</p>
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