<html>
<head>
<base href="https://llvm.org/bugs/" />
</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 --- - ROTATE by 1 instruction is preferable over ROTATE with immediate"
href="https://llvm.org/bugs/show_bug.cgi?id=30644">30644</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>ROTATE by 1 instruction is preferable over ROTATE with immediate
</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>Windows NT
</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>Backend: X86
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>zvi.rackover@intel.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org
</td>
</tr>
<tr>
<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>For the following test
define i32 @rotr1_32(i32 %A) {
%B = shl i32 %A, 31
%C = lshr i32 %A, 1
%D = or i32 %B, %C
ret i32 %D
}
We generate:
roll $31, %eax
It would be better to generate:
rorl $eax
Rotate by 1 is translated to 1 micro-op, while rotate with imm8 is translated
to 2 micro-ops.
We appear to select to ROL1 instructions, but not the ROR1 instructions.</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>