<html>
<head>
<base href="http://llvm.org/bugs/" />
</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 --- - Optimization eliminates an overflow check."
href="http://llvm.org/bugs/show_bug.cgi?id=16642">16642</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Optimization eliminates an overflow check.
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
<tr>
<th>Version</th>
<td>3.3
</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>julsomp@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>The following simple function
long long f(long long x, long long y) {
long long r;
long long err = 0;
r = x * y;
err = y != 0 && r / y != x;
return err ? 0 : r;
}
clang -c -O1 -S bla.c
compiles to just
f: # @f
.cfi_startproc
# BB#0:
imulq %rsi, %rdi
movq %rdi, %rax
ret
.Ltmp0:
.size f, .Ltmp0-f
.cfi_endproc
which eliminates the attempted overflow checking, and therefore returns results
other than expected when x * y overflows.</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>