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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Local register variables using high-byte registers should cause a -Wgcc-compat warning"
href="https://bugs.llvm.org/show_bug.cgi?id=45918">45918</a>
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<th>Summary</th>
<td>Local register variables using high-byte registers should cause a -Wgcc-compat warning
</td>
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<th>Product</th>
<td>new-bugs
</td>
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<th>Version</th>
<td>unspecified
</td>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Linux
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>enhancement
</td>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>new bugs
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>josephcsible@gmail.com
</td>
</tr>
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<th>CC</th>
<td>htmldeveloper@gmail.com, llvm-bugs@lists.llvm.org
</td>
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<p>
<div>
<pre>Consider this C function:
char f(void) {
register char x __asm__("dh");
__asm__("movb $42, %%dh" : "=r"(x));
return x;
}
When compiled with Clang, it will return 42, as expected. However, GCC doesn't
distinguish between "dh" and "dl", so it returns whatever happened to be in %dl
instead. They don't consider this a bug
(<a href="https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95121">https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95121</a>) so likely won't be
changing it anytime soon. As such, we should emit a -Wgcc-compat warning for
local register variables using high-byte registers.</pre>
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