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<base href="https://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 --- - major vectorizer performance regression from 3.7.1"
href="https://llvm.org/bugs/show_bug.cgi?id=27008">27008</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>major vectorizer performance regression from 3.7.1
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
<tr>
<th>Version</th>
<td>3.8
</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>normal
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>-New Bugs
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>pdknsk@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr>
<tr>
<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>clang version 3.7.1 (tags/RELEASE_371/final)
Target: x86_64-unknown-linux-gnu
$ clang-3.7 -march=haswell -O2 -std=c99 file.c -o file
$ ./file
1048575999 0.340
clang version 3.8.0 (tags/RELEASE_380/final)
Target: x86_64-unknown-linux-gnu
$ clang-3.8 -march=haswell -O2 -std=c99 file.c -o file
$ ./file
1048575999 0.986
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
int function(const char* mem, const int x) {
int r = 0;
for (unsigned int i = 1; i < x; i++)
r += (mem[i - 1] != mem[i]);
return r;
}
int main() {
int x = 1000 << 20;
char* mem = (char*)malloc(x);
for (int y = 0; y < x; y++)
mem[y] = y & 1;
int c = clock();
int r = function(mem, x);
printf("%i %.3f\n", r, (float)(clock() - c) / CLOCKS_PER_SEC);
}</pre>
</div>
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