<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 - Simple C program produces different output if compiled with -O1 instead of -O0"
href="https://bugs.llvm.org/show_bug.cgi?id=44424">44424</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Simple C program produces different output if compiled with -O1 instead of -O0
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
<tr>
<th>Version</th>
<td>unspecified
</td>
</tr>
<tr>
<th>Hardware</th>
<td>Macintosh
</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>C++
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>dirk.hoffmann@me.com
</td>
</tr>
<tr>
<th>CC</th>
<td>blitzrakete@gmail.com, dgregor@apple.com, erik.pilkington@gmail.com, llvm-bugs@lists.llvm.org, richard-llvm@metafoo.co.uk
</td>
</tr></table>
<p>
<div>
<pre>Test program: main.cpp
#include <stdint.h>
#include <stdio.h>
bool foo(uint32_t x, uint32_t y)
{
uint32_t z = (uint16_t)x * (uint16_t)y;
return z & 0x80000000;
}
int main(int argc, char *argv[])
{
printf("%d\n", foo(0x7FFFF, 0x7FFFF));
}
Compiler:
Apple clang version 11.0.0 (clang-1100.0.33.8)
Target: x86_64-apple-darwin18.7.0
Thread model: posix
Output:
<span class="quote">> clang -O0 main.cpp; ./a.out </span >
1
<span class="quote">> clang -O1 main.cpp; ./a.out </span >
0</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>