<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 - wrong code with -disable-licm-promotion -enable-loop-distribute"
href="https://bugs.llvm.org/show_bug.cgi?id=38699">38699</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>wrong code with -disable-licm-promotion -enable-loop-distribute
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</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>Loop Optimizer
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>paulsson@linux.vnet.ibm.com
</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=20767" name="attach_20767" title="reduced testcase">attachment 20767</a> <a href="attachment.cgi?id=20767&action=edit" title="reduced testcase">[details]</a></span>
reduced testcase
Thanks to (for the) nice output of opt-viewer with the optimization remarks, I
tried the loop-distribute pass on a benchmark and got a huge speedup as
vectorization occurred (30%) :-)
I then enabled this in csmith testing and found a wrong code bug which I
reduced to:
a, b, c, d, e;
main() {
for (; b > -8; --b) {
c = 0;
for (; c != -14; c--) {
if (b)
break;
--d;
}
}
for (; e < 5; e++)
a = c;
printf("checksum = %X\n", a);
}
gcc -O1 -march=z10 -o a.out -w
gcc -O0 -march=z13 -o a.out -w
gcc -O1 -march=z13 -o a.out -w
clang -O0 -march=z10 -o a.out -w
clang -O0 -march=z13 -o a.out -w
clang -O3 -march=z10 -o a.out -w
clang -O3 -march=z13 -o a.out -w
clang -O3 -march=z13 -o a.out -w -mllvm -disable-licm-promotion -mllvm
-enable-loop-distribute
checksum = 0
checksum = 0
checksum = 0
checksum = 0
checksum = 0
checksum = 0
checksum = 0
checksum = 0
checksum = FFFFFFF2</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>