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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - __BIGGEST_ALIGNMENT__ not the same as gcc for AVX and later"
href="https://bugs.llvm.org/show_bug.cgi?id=42554">42554</a>
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<th>Summary</th>
<td>__BIGGEST_ALIGNMENT__ not the same as gcc for AVX and later
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<th>Product</th>
<td>clang
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<th>Version</th>
<td>8.0
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<th>Hardware</th>
<td>PC
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<th>OS</th>
<td>Linux
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
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<th>Priority</th>
<td>P
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<th>Component</th>
<td>C
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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<th>Reporter</th>
<td>clang@gmch.uk
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<th>CC</th>
<td>blitzrakete@gmail.com, dgregor@apple.com, erik.pilkington@gmail.com, llvm-bugs@lists.llvm.org, richard-llvm@metafoo.co.uk
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<pre>When compiled -march=native (on znver1) with gcc and clang I get the following:
* gcc 9.1.1 20190503 (Red Hat 9.1.1-1)
alignof(max_align_t)=16 __BIGGEST_ALIGNMENT__=32 malloc() align=16
__SSE__ __AVX__ __AVX2__
* clang 8.0.0 (Fedora 8.0.0-1.fc30)
(4.2.1 Compatible Clang 8.0.0 (Fedora 8.0.0-1.fc30))
alignof(max_align_t)=16 __BIGGEST_ALIGNMENT__=16 malloc() align=16
__SSE__ __AVX__ __AVX2__
When compiled without -march=native, both give:
alignof(max_align_t)=16 __BIGGEST_ALIGNMENT__=16 malloc() align=16
__SSE__
My guess is that clang's __BIGGEST_ALIGNMENT__ for -march=native is a bug...
except that gcc v4.2.1 predates AVX ???
FWIW: in all cases glibc malloc() aligned to 16. My reading of the glibc code
tells me that its alignment is 2*sizeof(size_t), which is in fact the same as
alignof(max_align_t), but is in no way related.</pre>
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