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<base href="https://bugs.llvm.org/">
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - USRA is replaced with USHR+ORR which results in poor codegen"
href="https://bugs.llvm.org/show_bug.cgi?id=49577">49577</a>
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<th>Summary</th>
<td>USRA is replaced with USHR+ORR which results in poor codegen
</td>
</tr>
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<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Linux
</td>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>enhancement
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Backend: AArch64
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>kutdanila@yandex.ru
</td>
</tr>
<tr>
<th>CC</th>
<td>arnaud.degrandmaison@arm.com, llvm-bugs@lists.llvm.org, smithp352@googlemail.com, Ties.Stuij@arm.com
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</tr></table>
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<div>
<pre>int MoveMask(uint8x16_t input)
{
uint16x8_t high_bits = vreinterpretq_u16_u8(vshrq_n_u8(input, 7));
uint32x4_t paired16 =
vreinterpretq_u32_u16(vsraq_n_u16(high_bits, high_bits, 7));
uint64x2_t paired32 =
vreinterpretq_u64_u32(vsraq_n_u32(paired16, paired16, 14));
uint8x16_t paired64 =
vreinterpretq_u8_u64(vsraq_n_u64(paired32, paired32, 28));
return vgetq_lane_u8(paired64, 0) | ((int) vgetq_lane_u8(paired64, 8) <<
8);
}
Generates for vsraq_n_u16 and vsraq_n_u32 USHR+ORR instead of USRA like GCC
does
<a href="https://gcc.godbolt.org/z/MxP63x">https://gcc.godbolt.org/z/MxP63x</a>
Also in Match function there are two redundant AND with 0xff
Match(unsigned char): // @Match(unsigned char)
adrp x8, ctrl
ldr q0, [x8, :lo12:ctrl]
dup v1.16b, w0
cmeq v0.16b, v1.16b, v0.16b
movi v1.16b, #1
and v0.16b, v0.16b, v1.16b
ushr v1.8h, v0.8h, #7
orr v0.16b, v1.16b, v0.16b
ushr v1.4s, v0.4s, #14
orr v0.16b, v1.16b, v0.16b
usra v0.2d, v0.2d, #28
umov w8, v0.b[0]
umov w9, v0.b[8]
and x0, x8, #0xff // Not needed?
and x8, x9, #0xff // Not needed?
bfi x0, x8, #8, #8
ret</pre>
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