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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - [AArch64] Optimise xtn+xtn to uzp"
href="https://bugs.llvm.org/show_bug.cgi?id=52298">52298</a>
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<th>Summary</th>
<td>[AArch64] Optimise xtn+xtn to uzp
</td>
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<th>Product</th>
<td>libraries
</td>
</tr>
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<th>Version</th>
<td>trunk
</td>
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<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>
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<tr>
<th>Keywords</th>
<td>beginner
</td>
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<th>Severity</th>
<td>enhancement
</td>
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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>pavel.iliin@arm.com
</td>
</tr>
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<th>CC</th>
<td>arnaud.degrandmaison@arm.com, llvm-bugs@lists.llvm.org, smithp352@googlemail.com, Ties.Stuij@arm.com
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<p>
<div>
<pre>Optimise truncate operations with a hi/lo pair into a single permute of half
the bit size of the input and just ignoring the top bits (which are truncated
out).
void d2 (short * restrict a, int *b, int n) {
for (int i = 0; i < n; i++)
a[i] = b[i];
}
clang -O3 generates
ldp q0, q1, [x9, #-16]
add x9, x9, #32
subs x8, x8, #8
xtn v0.4h, v0.4s
xtn v1.4h, v1.4s
stur d0, [x10, #-8]
str d1, [x10], #16
b.ne .LBB0_2
gcc -O3 combines the two `xtn`s into a `uzp`
ldp q0, q1, [x1]
add x1, x1, 32
uzp1 v0.8h, v0.8h, v1.8h
str q0, [x0], 16
cmp x1, x2
bne .L3
<a href="https://godbolt.org/z/dYozq6GPh">https://godbolt.org/z/dYozq6GPh</a>
gcc commit
<a href="https://github.com/gcc-mirror/gcc/commit/52da40ffe2aaf086f622e513cc99a64bc7573a67#diff-e55f82ad6f42cf1df30ab3fffeba1fd00aea748d04e231dda6f247b5c7e1c35a">https://github.com/gcc-mirror/gcc/commit/52da40ffe2aaf086f622e513cc99a64bc7573a67#diff-e55f82ad6f42cf1df30ab3fffeba1fd00aea748d04e231dda6f247b5c7e1c35a</a></pre>
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