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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 -O1. (X86_DAG->DAG_Instruction_Selection_on_function)"
href="https://bugs.llvm.org/show_bug.cgi?id=37060">37060</a>
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<th>Summary</th>
<td>Clang miscompiles with -O1. (X86_DAG->DAG_Instruction_Selection_on_function)
</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>
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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>
<tr>
<th>Component</th>
<td>new bugs
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<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 testcase starting from optimization level -O1. opt-bisect
points to X86_DAG->DAG_Instruction_Selection_on_function.
Reproducer:
<span class="quote">>$ cat main.c</span >
#include <stdio.h>
const int b = 1545269876;
const int c = -1355305896;
const int * d = &(b);
int e = -1421384539;
extern void tf_0_foo();
int main () {
tf_0_foo ();
printf("%d\n", e);
return 0;
}
<span class="quote">>$ cat func.c</span >
extern const int tf_0_var_6;
extern const int c;
extern int e;
extern const int * d;
void tf_0_foo() {
short a = ~0 % c;
e = (unsigned char)(a ^ *d);
}
Error:
<span class="quote">>$ clang -w -O0 main.c func.c ; ./a.out</span >
139
<span class="quote">>$ clang -w -O3 main.c func.c ; ./a.out</span >
-117
LLVM version:
clang version 7.0.0 (trunk 329488)
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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