<html>
<head>
<base href="https://bugs.llvm.org/">
</head>
<body><table border="1" cellspacing="0" cellpadding="8">
<tr>
<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=37820">37820</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Clang miscompiles with optimization level -O1 and higher
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
<tr>
<th>OS</th>
<td>Linux
</td>
</tr>
<tr>
<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>LLVM Codegen
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedclangbugs@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>Created <span class=""><a href="attachment.cgi?id=20433" name="attach_20433" title="Reproducer.">attachment 20433</a> <a href="attachment.cgi?id=20433&action=edit" title="Reproducer.">[details]</a></span>
Reproducer.
Clang produces incorrect code with -O1 and higher.
Opt-bisect-limit points to X86 DAG->DAG Instruction Selection on function.
Reproducer:
<span class="quote">>$ cat func.c</span >
extern unsigned long a;
extern long b, c;
void foo() {
b = (unsigned int)(a >> ((-16384L & c) + 4503359447364223024));
}
<span class="quote">>$ cat driver.c</span >
#include <stdio.h>
unsigned long a = 10144615248613568396UL;
long b, c = -4503359447364216586L;
void foo();
int main() {
foo();
printf("%lu\n", b);
}
Error:
<span class="quote">>$ clang -O0 driver.c func.c ; ./a.out</span >
36040
<span class="quote">>$ clang -O1 driver.c func.c ; ./a.out</span >
3640036552
LLVM version:
clang version 7.0.0 (trunk 334837)
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>
</div>
</p>
<hr>
<span>You are receiving this mail because:</span>
<ul>
<li>You are on the CC list for the bug.</li>
</ul>
</body>
</html>