<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 - [InstCombine] and-mask + conditional "sext" -> and-mask + sext"
href="https://bugs.llvm.org/show_bug.cgi?id=42412">42412</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>[InstCombine] and-mask + conditional "sext" -> and-mask + sext
</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>lebedev.ri@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>There's also identical problem to <a class="bz_bug_link
bz_status_NEW "
title="NEW - InstCombine: lshr + "sext" => ashr canonicalization"
href="show_bug.cgi?id=42389">https://bugs.llvm.org/show_bug.cgi?id=42389</a>
with different bit buffer abstraction:
<a href="https://godbolt.org/z/po3_0Y">https://godbolt.org/z/po3_0Y</a>
<a href="https://rise4fun.com/Alive/btQ">https://rise4fun.com/Alive/btQ</a>
int bad(unsigned input, unsigned len) {
unsigned diff = input & ((1 << len)-1);
// If the first bit is 1 we need to turn this into a negative number
if (diff >> (len - 1))
diff -= (1 << len);
return diff;
}
int good(unsigned input, unsigned len) {
unsigned diff = input & ((1 << len)-1);
diff <<= (32-len);
diff = int(diff) >> (32-len);
return diff;
}
Name:
%o3 = shl i32 1, %len
%o4 = add nsw i32 %o3, -1
%o5 = and i32 %o4, %data
%o6 = add i32 %len, -1
%o7 = lshr i32 %o5, %o6
%o8 = icmp eq i32 %o7, 0
%o9 = select i1 %o8, i32 0, i32 %o3
%r = sub i32 %o5, %o9
=>
%n3 = shl nsw i32 -1, %len
%n4 = xor i32 %n3, -1
%n5 = and i32 %n4, %data
%n6 = sub i32 32, %len
%n7 = shl i32 %n5, %n6
%r = ashr i32 %n7, %n6
Did not analyse this one yet.</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>