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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - clang-cl incorrectly interprets /Zp8 flag"
href="https://bugs.llvm.org/show_bug.cgi?id=45420">45420</a>
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<th>Summary</th>
<td>clang-cl incorrectly interprets /Zp8 flag
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<th>Product</th>
<td>clang
</td>
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<th>Version</th>
<td>trunk
</td>
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<th>Hardware</th>
<td>PC
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<th>OS</th>
<td>Windows NT
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<th>Status</th>
<td>NEW
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<th>Severity</th>
<td>normal
</td>
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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>anton@gaijin.team
</td>
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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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<p>
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<pre>According to documentation,
<a href="https://docs.microsoft.com/en-us/cpp/build/reference/zp-struct-member-alignment?view=vs-2019">https://docs.microsoft.com/en-us/cpp/build/reference/zp-struct-member-alignment?view=vs-2019</a>
Visual studio interprets /Zp8 as a way to pack structure members, but it
doesn't not change alignment of such struct itself.
clang-cl interprets it similar to -fpack-struct=8, and so /Zp8 flag is working
significantly differently in msvc and clang-cl.
According to documentation WindowsSDK headers has to be compiled with /Zp8
flag, and so it can cause (and is causing in some projects) issues with using
clang-cl as replacement for msvc.
the following sample:
```
#include <emmintrin.h>
struct A{__m128 a[1];};
static_assert(alignof(A) == 16, "should be aligned");
```
won't compile with /Zp8 flag with clang-cl, but it will in msvc.
Run-time sample:
<a href="https://godbolt.org/z/qh7Dbg">https://godbolt.org/z/qh7Dbg</a></pre>
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