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<base href="https://bugs.llvm.org/">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Wrong size of struct with overaligned bitfield"
href="https://bugs.llvm.org/show_bug.cgi?id=48875">48875</a>
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<th>Summary</th>
<td>Wrong size of struct with overaligned bitfield
</td>
</tr>
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<th>Product</th>
<td>clang
</td>
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<th>Version</th>
<td>11.0
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Linux
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>C
</td>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
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</tr>
<tr>
<th>Reporter</th>
<td>ju.orth@gmail.com
</td>
</tr>
<tr>
<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>
<div>
<pre>Consider
struct Y {
__declspec(align(128)) int i:1;
};
struct Z {
char c;
struct Y y;
};
int f(void) {
return _Alignof(struct Y);
}
int g(void) {
return sizeof(struct Z);
}
int h(void) {
return &((struct Z *)0)->y; // offsetof(struct Z, y)
}
MSVC returns
128
16
8
clang returns
128
256
128
on the aarch64-pc-windows-msvc target.
Apparently, on ARM targets, bitfields in structs increase the alignment of the
struct to at most 8 bytes. Even though _Alignof incorrectly returns a higher
value.</pre>
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