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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - [X86][SSE] BLENDV Simplification to AND/ANDN"
href="https://bugs.llvm.org/show_bug.cgi?id=38814">38814</a>
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<th>Summary</th>
<td>[X86][SSE] BLENDV Simplification to AND/ANDN
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<th>Product</th>
<td>libraries
</td>
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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>Windows NT
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>enhancement
</td>
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<th>Priority</th>
<td>P
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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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<th>Reporter</th>
<td>llvm-dev@redking.me.uk
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<th>CC</th>
<td>andrea.dibiagio@gmail.com, craig.topper@gmail.com, llvm-bugs@lists.llvm.org, spatel+llvm@rotateright.com
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<p>
<div>
<pre>In cases where the _mm_blendv_* intrinsics are used with zero/allbits
true/false operands it'd be better to simplify to and/andnot bit operations if
we know the select operand is 'all sign bits'.
This might be even worth it for any true/false operands but we sometimes fail
to convert this back to VSELECT.
<a href="https://gcc.godbolt.org/z/K_7Zd9">https://gcc.godbolt.org/z/K_7Zd9</a>
__m128 sel_v4f32(__m128 *x, __m128 y, __m128 z) {
return _mm_blendv_ps(*x, _mm_setzero_ps(), _mm_cmpgt_ps(y, z));
}
_Z9sel_v4f32PDv4_fS_S_:
vmovaps (%rdi), %xmm2
vcmpltps %xmm0, %xmm1, %xmm0
vxorps %xmm1, %xmm1, %xmm1
vblendvps %xmm0, %xmm1, %xmm2, %xmm0
retq
But could be just vcmpps + vandps/vandnps, allowing further combines,
commutation etc.</pre>
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</p>
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