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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 - Clang miscompiles with optimization level -O1 and higher"
href="https://bugs.llvm.org/show_bug.cgi?id=37667">37667</a>
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<th>Summary</th>
<td>Clang miscompiles with optimization level -O1 and higher
</td>
</tr>
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<th>Product</th>
<td>clang
</td>
</tr>
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<th>Version</th>
<td>trunk
</td>
</tr>
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<th>Hardware</th>
<td>PC
</td>
</tr>
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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>
</tr>
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<th>Component</th>
<td>LLVM Codegen
</td>
</tr>
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<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>Vsevolod.Livinskij@frtk.ru
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>Clang miscompiles with optimization level -O1 and higher.
opt-bisect-limit points to X86 DAG->DAG Instruction Selection on function
Reproducer:
<span class="quote">>$ cat repr.c</span >
#include <stdio.h>
int a, b = 918, c;
unsigned d = 8089;
void foo() {
a = (unsigned char)(c | b % d);
}
int main() {
foo();
printf("%d\n", a);
}
Error:
<span class="quote">>$ clang -O0 repr.c ; ./a.out</span >
150
<span class="quote">>$ clang -O1 repr.c ; ./a.out</span >
918
LLVM version:
clang version 7.0.0 (trunk 333836)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /llvm/bin-trunk/bin
Found candidate GCC installation: /usr/lib/gcc/x86_64-redhat-linux/4.4.7
Found candidate GCC installation: /usr/lib/gcc/x86_64-redhat-linux/4.8.2
Found candidate GCC installation: /usr/lib/gcc/x86_64-redhat-linux/4.8.5
Selected GCC installation: /usr/lib/gcc/x86_64-redhat-linux/4.8.5
Candidate multilib: .;@m64
Candidate multilib: 32;@m32
Selected multilib: .;@m64</pre>
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