<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 - __builtin_mul_overflow with mixed sign gives different results compared to GCC"
href="https://bugs.llvm.org/show_bug.cgi?id=38665">38665</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>__builtin_mul_overflow with mixed sign gives different results compared to GCC
</td>
</tr>
<tr>
<th>Product</th>
<td>clang
</td>
</tr>
<tr>
<th>Version</th>
<td>7.0
</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>LLVM Codegen
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>joerg@NetBSD.org
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>Try to build:
#include <stddef.h>
int f(size_t a, size_t b) {
ptrdiff_t x;
return __builtin_mul_overflow(a, b, &x);
}
with clang and gcc for x86_64.
(1) GCC seems to interpret this as uint64_t x uint64_t -> uint64_t
multiplication
(2) Clang seems to widen the types and goes for int128_t instead (__muloti4).
This difference in interpretation seems to break the memory overflow checks in
GNU m4.</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>