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<base href="https://bugs.llvm.org/">
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<body><table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Improve codegen for shift by constant"
href="https://bugs.llvm.org/show_bug.cgi?id=46281">46281</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Improve codegen for shift by constant
</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>Backend: X86
</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>craig.topper@gmail.com, llvm-bugs@lists.llvm.org, llvm-dev@redking.me.uk, spatel+llvm@rotateright.com
</td>
</tr></table>
<p>
<div>
<pre>typedef char v16qi __attribute__ ((vector_size (16)));
typedef char v32qi __attribute__ ((vector_size (32)));
v16qi ashiftrt (v16qi a)
{
return a>>5;
}
v32qi arshiftrt2 (v32qi a)
{
return a>>5;
}
Clang -g0 -O3 -march=skylake
.LCPI0_0:
.zero 16,7
.LCPI0_1:
.zero 16,4
ashiftrt(char __vector(16)): # @ashiftrt(char
__vector(16))
vpsrlw xmm0, xmm0, 5
vpand xmm0, xmm0, xmmword ptr [rip + .LCPI0_0]
vmovdqa xmm1, xmmword ptr [rip + .LCPI0_1] # xmm1 =
[4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4]
vpxor xmm0, xmm0, xmm1
vpsubb xmm0, xmm0, xmm1
ret
.LCPI1_0:
.zero 32,7
.LCPI1_1:
.zero 32,4
arshiftrt2(char __vector(32)): # @arshiftrt2(char
__vector(32))
vpsrlw ymm0, ymm0, 5
vpand ymm0, ymm0, ymmword ptr [rip + .LCPI1_0]
vmovdqa ymm1, ymmword ptr [rip + .LCPI1_1] # ymm1 =
[4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4]
vpxor ymm0, ymm0, ymm1
vpsubb ymm0, ymm0, ymm1
ret
ICC -g0 -O3 -march=skylake
ashiftrt(char __vector(16)):
vpsrlw xmm1, xmm0, 5 #6.16
vpand xmm0, xmm1, XMMWORD PTR .L_2il0floatpacket.0[rip] #6.16
ret #6.16
arshiftrt2(char __vector(32)):
vpsrlw ymm1, ymm0, 5 #11.16
vpand ymm0, ymm1, YMMWORD PTR .L_2il0floatpacket.1[rip] #11.16
ret #11.16
.L_2il0floatpacket.1:
.long
0x07070707,0x07070707,0x07070707,0x07070707,0x07070707,0x07070707,0x07070707,0x07070707
.L_2il0floatpacket.0:
.long 0x07070707,0x07070707,0x07070707,0x07070707
Godbolt: <a href="https://godbolt.org/z/LAibFf">https://godbolt.org/z/LAibFf</a></pre>
</div>
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