<html>
<head>
<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 --- - trunk's optimizer generates slower code than 3.5"
href="http://llvm.org/bugs/show_bug.cgi?id=22058">22058</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>trunk's optimizer generates slower code than 3.5
</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>MacOS X
</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>191919@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>Created <span class=""><a href="attachment.cgi?id=13605" name="attach_13605" title="Assembly and executable files">attachment 13605</a> <a href="attachment.cgi?id=13605&action=edit" title="Assembly and executable files">[details]</a></span>
Assembly and executable files
clang 3.6 svn (trunk 224979 as the time I was to report this problem) generates
slower code than 3.5 (Apple LLVM version 6.0 (clang-600.0.56) (based on LLVM
3.5svn)) for the following code.
It is a "8 queens puzzle" solver written as an educational example. As compiled
by both clang 3.5 and 3.6, it gave the correct answer, but clang 3.5 generates
code which runs 20% faster than 3.6.
##########################################
# clang 3.5 which comes with Xcode 6.1.1
##########################################
$ clang -O3 -mssse3 -fomit-frame-pointer -fno-stack-protector -fno-exceptions
-o 8 8.c
$ time ./8 9 # 9 queens
352 solutions
$ time ./8 10 # 10 queens
./8 9 1.63s user 0.00s system 99% cpu 1.632 total
724 solutions
./8 10 45.11s user 0.01s system 99% cpu 45.121 total
##########################################
# clang 3.6 svn trunk
##########################################
$ /opt/bin/clang -O3 -mssse3 -fomit-frame-pointer -fno-stack-protector
-fno-exceptions -o 8 8.c
$ time ./8 9 # 9 queens
352 solutions
./8 9 2.07s user 0.00s system 99% cpu 2.078 total
$ time ./8 10 # 10 queens
724 solutions
./8 10 56.63s user 0.02s system 99% cpu 56.650 total
The source code is below, I also attached the executable files as well as the
assembly code files for clang 3.5 and 3.6 by IDA.
```
#include <stdio.h>
#include <stdlib.h>
static inline int validate(int* a, int d)
{
int i, j, x;
for (i = 0; i < d; ++i)
{
for (j = i+1, x = 1; j < d; ++j, ++x)
{
const int d = a[i] - a[j];
if (d == 0 || d == -x || d == x) return 0;
}
}
return 1;
}
static inline int solve(int d)
{
int r = 0;
int* a = (int*) calloc(sizeof(int), d+1);
int p = d - 1;
for (;;)
{
a[p]++;
if (a[p] > d-1)
{
int bp = p - 1;
while (bp >= 0)
{
a[bp]++;
if (a[bp] <= d-1) break;
a[bp] = 0;
--bp;
}
if (bp < 0)
break;
a[p] = 0;
}
if (validate(a, d))
{
++r;
}
}
free(a);
return r;
}
int main(int argc, char** argv)
{
if (argc != 2) return -1;
int r = solve((int) strtol(argv[1], NULL, 10));
printf("%d solutions\n", r);
}
```</pre>
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