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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 --- - Failure to beneficially vectorize 'copyable' elements in integer binary ops"
href="https://llvm.org/bugs/show_bug.cgi?id=30787">30787</a>
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<th>Summary</th>
<td>Failure to beneficially vectorize 'copyable' elements in integer binary ops
</td>
</tr>
<tr>
<th>Product</th>
<td>new-bugs
</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>Windows NT
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>new bugs
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>llvm-dev@redking.me.uk
</td>
</tr>
<tr>
<th>CC</th>
<td>a.bataev@hotmail.com, andrew.v.tischenko@gmail.com, llvm-bugs@lists.llvm.org, mkuper@google.com, spatel+llvm@rotateright.com
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</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>We successfully vectorize:
// clang -O3 -march=btver2
void add0(int * __restrict dst, const int * __restrict src) {
*dst++ = *src++ + 1;
*dst++ = *src++ + 1;
*dst++ = *src++ + 2;
*dst++ = *src++ + 3;
}
add0(int*, int const*):
vmovdqu xmm0, xmmword ptr [rsi]
vpaddd xmm0, xmm0, xmmword ptr [rip + .LCPI0_0]
vmovdqu xmmword ptr [rdi], xmm0
ret
But fail to do so if one or more elements simplify to a simple copy. If the
cost model says it would still be beneficial we should vectorize such cases:
void add1(int * __restrict dst, const int * __restrict src) {
*dst++ = *src++ + 0;
*dst++ = *src++ + 1;
*dst++ = *src++ + 2;
*dst++ = *src++ + 3;
}
add1(int*, int const*):
mov ecx, dword ptr [rsi + 4]
mov eax, dword ptr [rsi]
mov edx, dword ptr [rsi + 8]
inc ecx
mov dword ptr [rdi], eax
add edx, 2
mov dword ptr [rdi + 4], ecx
mov ecx, dword ptr [rsi + 12]
mov dword ptr [rdi + 8], edx
add ecx, 3
mov dword ptr [rdi + 12], ecx
ret
Similarly for SUB/MUL/SHL/LSHR/ASHR (DIV/REM?). Possibly for -ffast-math float
FADD/FSUB/FMUL/FDIV operations as well.
Further examples can be found here: <a href="https://godbolt.org/g/ueIYiF">https://godbolt.org/g/ueIYiF</a></pre>
</div>
</p>
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