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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Add warnings about violation of aliasing rules"
href="https://bugs.llvm.org/show_bug.cgi?id=50722">50722</a>
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<th>Summary</th>
<td>Add warnings about violation of aliasing rules
</td>
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<th>Product</th>
<td>clang
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<th>Version</th>
<td>12.0
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<th>Hardware</th>
<td>All
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<th>OS</th>
<td>All
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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
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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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<th>Reporter</th>
<td>tk@tkoenig.net
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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>The following, rather horrible code (which came off a Usenet discussion)
violates C aliasing rules in several places:
#include <stdio.h>
typedef unsigned char uchar;
int
main ()
{
double d = 2.34;
int i[2];
printf ("%lf\n", d);
*(long *)i = *(long *)&d;
((int *)&d)[0] = i[0];
((int *)&d)[1] = i[1];
printf ("%.15lf\n", d);
((uchar *)&d)[2] += 123;
printf ("%.15lf\n", d);
return 0;
}
It would be nice if clang could warn or issue an error about the lines
*(long *)i = *(long *)&d;
*(long *)i = *(long *)&d;
((int *)&d)[0] = i[0];
with suitable options (preferably -Wall).</pre>
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