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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 --- - very slow compilation at -O3 on x86_64-pc-linux-gnu"
href="http://llvm.org/bugs/show_bug.cgi?id=17461">17461</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>very slow compilation at -O3 on x86_64-pc-linux-gnu
</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>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>su@cs.ucdavis.edu
</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>The following code takes very long time (> 200 seconds) to compile at -O3 using
the current clang-trunk and clang 3.3 on x86_64-linux.
It appears to be a regression from clang 3.2.
$ clang-trunk -v
clang version 3.4 (trunk 191812)
Target: x86_64-pc-linux-gnu
Thread model: posix
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.4
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.4.6
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.4.7
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.6
Found candidate GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.6.3
Selected GCC installation: /usr/lib/gcc/x86_64-linux-gnu/4.6
$
$ time clang-trunk -O2 reduced.c
0.44user 0.02system 0:00.79elapsed 59%CPU (0avgtext+0avgdata 58208maxresident)k
0inputs+32outputs (0major+6773minor)pagefaults 0swaps
$
$ time clang-3.2 -O3 reduced.c
0.04user 0.01system 0:00.16elapsed 33%CPU (0avgtext+0avgdata 49008maxresident)k
0inputs+32outputs (0major+5596minor)pagefaults 0swaps
$
$ time clang-trunk -O3 reduced.c
213.58user 0.15system 5:30.50elapsed 64%CPU (0avgtext+0avgdata
62192maxresident)k
0inputs+32outputs (0major+7066minor)pagefaults 0swaps
$
$ time clang-3.3 -O3 reduced.c
225.18user 0.09system 5:40.19elapsed 66%CPU (0avgtext+0avgdata
58640maxresident)k
0inputs+32outputs (0major+6803minor)pagefaults 0swaps
$
$ time gcc-trunk -O3 reduced.c
0.03user 0.00system 0:00.13elapsed 32%CPU (0avgtext+0avgdata 45024maxresident)k
0inputs+32outputs (0major+7113minor)pagefaults 0swaps
$
$ time icc -O3 reduced.c
0.24user 1.94system 0:03.80elapsed 57%CPU (0avgtext+0avgdata 81392maxresident)k
0inputs+192outputs (0major+16473minor)pagefaults 0swaps
$
$
------------------------------------------
char c;
static char *z = &c;
int a, b, g, *m, n, *w = &n, **x = &w;
volatile unsigned int d, *u = &d, **v = &u;
short sum (short p1, short p2)
{
return p1 + p2;
}
unsigned int
foo (int p1)
{
m = &p1;
return a;
}
short bar (short p1, short p2, unsigned p3)
{
unsigned t1 = 0;
unsigned short t2 = 0;
for (n = 0; n < 4; ++n)
{
int i = t2--;
if (*z < t2)
return **x;
for (g = 0; g < 13; g = sum (g, 1))
for (i = 0; i < 39; i++)
{
t1 = foo (p2);
t1 = (p3 <= t1) || d;
}
}
return p1;
}
static short
baz ()
{
short t3 = 0;
int t4 = 0;
int *t5 = &t4;
for (b = 0; b < 4; b++)
{
int t6 = 1;
t3 = bar (*t5, t6, t6);
bar (t3, t6, *t5);
}
return **x;
}
int
main ()
{
baz ();
return 0;
}</pre>
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