<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 canonicalization for usub.sat(a, b) + b"
href="https://bugs.llvm.org/show_bug.cgi?id=42178">42178</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Missed canonicalization for usub.sat(a, b) + b
</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>#define T unsigned
T do_shift(T a, T b)
{
return a - ((a - b) & - (T)(a < b));
}
Current trunk:
do_shift: # @do_shift
xor eax, eax
sub esi, edi
cmovae eax, esi
add eax, edi
ret
Clang 8:
do_shift: # @do_shift
mov eax, edi
cmp esi, edi
cmova eax, esi
ret
define dso_local i32 @do_shift(i32, i32) local_unnamed_addr #0 {
%3 = tail call i32 @llvm.usub.sat.i32(i32 %1, i32 %0)
%4 = add i32 %3, %0
ret i32 %4
}
As noted by nikic: "Looks like an instcombine fail: usub.sat(a, b) + b should
be canonicalized to umax(a, b)."</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>