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<base href="https://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - inefficient code for i16 bit"
href="https://llvm.org/bugs/show_bug.cgi?id=31667">31667</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>inefficient code for i16 bit
</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>All
</td>
</tr>
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<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>asaf.badouh@intel.com
</td>
</tr>
<tr>
<th>Reporter</th>
<td>asaf.badouh@intel.com
</td>
</tr>
<tr>
<th>CC</th>
<td>amjad.aboud@intel.com, llvm-bugs@lists.llvm.org
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>Given:
define i16 @test(i16 %data) {
entry:
%shr1 = lshr i16 %data, 1
%shr1.1 = lshr i16 %data, 3
%ret = sub i16 %shr1.1, %shr1
ret i16 %ret
}
Generated asm:
movl %ecx, %eax
andl $65528, %eax # imm = 0xFFF8
andl $65534, %ecx # imm = 0xFFFE
shrl %ecx
shrl $3, %eax
subl %ecx, %eax
retq
The optimal expected asm:
andl $65535, %eax # imm = 0xFFFF
movl %eax, %ecx
shrl %ecx
shrl $3, %eax
subl %ecx, %eax
retq</pre>
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