<html>
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<base href="http://llvm.org/bugs/" />
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<body><table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - incorrect loop optimization at O2"
href="http://llvm.org/bugs/show_bug.cgi?id=16602">16602</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>incorrect loop optimization at O2
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
<tr>
<th>Version</th>
<td>3.2
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
<tr>
<th>OS</th>
<td>All
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</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>halayli@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvmbugs@cs.uiuc.edu
</td>
</tr>
<tr>
<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>#include <stdio.h>
#include <stdlib.h>
#include <pthread.h>
int x = 23;
int y = 29;
void* set_x(void* arg)
{
(void)arg;
x = 29;
return NULL;
}
int main(void)
{
pthread_t p1;
pthread_create(&p1, NULL, set_x, NULL);
pthread_detach(p1);
while (x < y)
if (x == y)
break;
return 0;
}
The following code runs forever if compiled with -O2.
clang -Wall -Wextra test.c -pthread -o test && ./test
The assembly code generated causes in infinite loop jumping to LBB1_1.
.Ltmp8:
.cfi_def_cfa_register %rbp
subq $16, %rsp
leaq -8(%rbp), %rdi
xorl %esi, %esi
movl $set_x, %edx
xorl %ecx, %ecx
callq pthread_create
movq -8(%rbp), %rdi
callq pthread_detach
movl x(%rip), %eax
cmpl y(%rip), %eax
jge .LBB1_2
.align 16, 0x90
.LBB1_1: # %while.cond
# =>This Inner Loop Header: Depth=1
jmp .LBB1_1</pre>
</div>
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