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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][SSE] Failure to flip VPBLENDVB inputs with an inverted selection mask"
href="https://bugs.llvm.org/show_bug.cgi?id=42825">42825</a>
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<th>Summary</th>
<td>[X86][SSE] Failure to flip VPBLENDVB inputs with an inverted selection mask
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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
</td>
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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>craig.topper@gmail.com, llvm-bugs@lists.llvm.org, llvm-dev@redking.me.uk, spatel+llvm@rotateright.com
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<pre>Current Codegen: <a href="https://godbolt.org/z/hseT6Z">https://godbolt.org/z/hseT6Z</a>
__m128i sel2(__m128i x, __m128i y, __m128i s) {
return _mm_blendv_epi8(x, y, _mm_xor_si128(s, _mm_set1_epi32(-1)));
}
clang -g0 -O3 -march=btver2
define <2 x i64> @_Z4sel2Dv2_xS_S_(<2 x i64>, <2 x i64>, <2 x i64>) {
%4 = bitcast <2 x i64> %0 to <16 x i8>
%5 = bitcast <2 x i64> %1 to <16 x i8>
%6 = bitcast <2 x i64> %2 to <16 x i8>
%7 = xor <16 x i8> %6, <i8 -1, i8 -1, i8 -1, i8 -1, i8 -1, i8 -1, i8 -1, i8
-1, i8 -1, i8 -1, i8 -1, i8 -1, i8 -1, i8 -1, i8 -1, i8 -1>
%8 = tail call <16 x i8> @llvm.x86.sse41.pblendvb(<16 x i8> %4, <16 x i8> %5,
<16 x i8> %7) #2
%9 = bitcast <16 x i8> %8 to <2 x i64>
ret <2 x i64> %9
}
_Z4sel2Dv2_xS_S_:
vpcmpeqd %xmm3, %xmm3, %xmm3
vpxor %xmm3, %xmm2, %xmm2
vpblendvb %xmm2, %xmm1, %xmm0, %xmm0
retq
we should be able to flip the inputs and remove the selection mask inversion:
_Z4sel2Dv2_xS_S_:
vpblendvb %xmm2, %xmm0, %xmm1, %xmm0
retq</pre>
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