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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 code error"
href="https://bugs.llvm.org/show_bug.cgi?id=41764">41764</a>
</td>
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<tr>
<th>Summary</th>
<td>wrong code error
</td>
</tr>
<tr>
<th>Product</th>
<td>new-bugs
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>Linux
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>new bugs
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>amocywang@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>htmldeveloper@gmail.com, llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>I am not sure whether it is a bug. Maybe it is an undefined behaviour. I cannot
understand why the results are different at different optimization level.
Specially, if I change the int64_t to type int, the bug doesn't exist.
<span class="quote">> cat report.c</span >
typedef char int8_t;
typedef int int16_t;
typedef int uint16_t;
typedef long int64_t;
typedef char uint8_t;
typedef int uint32_t;
union a {
int64_t b;
uint16_t c;
} e;
int8_t d, l, h;
uint16_t *g = &e.c;
uint16_t **i = &g;
int16_t j;
uint16_t ***k = &i;
uint32_t m();
int8_t *n(uint16_t, uint32_t, uint16_t, union a, uint32_t);
uint32_t o() {
union a p = {};
m(n(d, 0, 0, p, d));
return l;
}
uint32_t m() {
int64_t *ad = &e.b;
*ad = 0;
int16_t *ae = &j;
*ae = ***k;
return h;
}
int8_t *n(uint16_t f, uint32_t ag, uint16_t ah, union a ai, uint32_t aj) {
int8_t *ak = &d;
(***k)++;
return ak;
}
int main() {
o();
printf("%d\n", j);
}
<span class="quote">> clang -v </span >
clang version 9.0.0 (trunk 356835) (llvm/trunk 356836)
......
<span class="quote">> clang report.c -O0 -o a0
> clang report.c -O2 -o a2
>./a0</span >
0
<span class="quote">>./a2</span >
1</pre>
</div>
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