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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 - [X86][AVX] Rematerializable lower 'allones' subvector masks"
href="https://bugs.llvm.org/show_bug.cgi?id=42653">42653</a>
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<th>Summary</th>
<td>[X86][AVX] Rematerializable lower 'allones' subvector masks
</td>
</tr>
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<th>Product</th>
<td>libraries
</td>
</tr>
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<th>Version</th>
<td>trunk
</td>
</tr>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>Windows NT
</td>
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<th>Status</th>
<td>NEW
</td>
</tr>
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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: X86
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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</tr>
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<th>Reporter</th>
<td>llvm-dev@redking.me.uk
</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
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<p>
<div>
<pre><a href="https://gcc.godbolt.org/z/ESwT78">https://gcc.godbolt.org/z/ESwT78</a>
We should be able to rematerialize masks where the lower subvector half is -1
and the upper 0 by using a smaller destination and the implicit zeroing of the
upper bits:
#include <x86intrin.h>
__m128i low128_128() {
// GOOD
return _mm_setr_epi32(-1,-1,-1,-1);
}
__m256i low256_128() {
// BAD: vpcmpeqd %xmm0, %xmm0, %xmm0
return _mm256_setr_epi32(-1,-1,-1,-1,0,0,0,0);
}
__m512i low512_128() {
// BAD: vpcmpeqd %xmm0, %xmm0, %xmm0
return _mm512_setr_epi32(-1,-1,-1,-1,0,0,0,0,0,0,0,0,0,0,0,0);
}
__m512i low512_256() {
// BAD: vpcmpeqd %ymm0, %ymm0, %ymm0
return _mm512_setr_epi32(-1,-1,-1,-1,-1,-1,-1,-1,0,0,0,0,0,0,0,0);
}</pre>
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