<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 - Missed bounds check optimization"
href="https://bugs.llvm.org/show_bug.cgi?id=47172">47172</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Missed bounds check optimization
</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>Scalar Optimizations
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>david.bolvansky@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>From rust-lang github (<a href="https://github.com/rust-lang/rust/issues/75525">https://github.com/rust-lang/rust/issues/75525</a>):
#include <stddef.h>
#include <stdint.h>
uint8_t f1(size_t idx) {
if (idx < 8) {
// it's ok that this has a bounds check
return (idx - 1) < 10;
} else {
return 0;
}
}
Clang:
f1: # @f1
cmp rdi, 8
setb cl
add rdi, -1
cmp rdi, 10
setb al
and al, cl
ret
GCC:
f1:
sub rdi, 1
cmp rdi, 6
setbe al
ret
Modified test case:
uint8_t f2(size_t idx) {
if (idx <= 9) {
return (idx - 1) > 10;
} else {
return 0;
}
}
Clang:
f2: # @f2
cmp rdi, 10
setb cl
add rdi, -1
cmp rdi, 10
seta al
and al, cl
ret
GCC:
f2:
test rdi, rdi
sete al
ret
<a href="https://godbolt.org/z/vahzbo">https://godbolt.org/z/vahzbo</a></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>