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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 - [SLPVectorizer] Failure to keep complex math vectorized"
href="https://bugs.llvm.org/show_bug.cgi?id=44008">44008</a>
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<th>Summary</th>
<td>[SLPVectorizer] Failure to keep complex math vectorized
</td>
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<th>Product</th>
<td>libraries
</td>
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<tr>
<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
</td>
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<th>Component</th>
<td>Scalar Optimizations
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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<th>Reporter</th>
<td>llvm-dev@redking.me.uk
</td>
</tr>
<tr>
<th>CC</th>
<td>a.bataev@hotmail.com, craig.topper@gmail.com, dtemirbulatov@gmail.com, llvm-bugs@lists.llvm.org, spatel+llvm@rotateright.com, v.porpodas@gmail.com
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<pre><a href="https://godbolt.org/z/YgBdFz">https://godbolt.org/z/YgBdFz</a>
#include <complex>
std::complex<float> mul_f32(std::complex<float> &A) {
return (2.0f * A);
}
std::complex<float> fma_f32(std::complex<float> &A, float B) {
return (2.0f * A) + B;
}
for the simple mul case we manage to keep the real+imag components vectorized
as a <2 x float>:
clang -g0 -O3 -march=btver2
mul_f32:
vmovsd (%rdi), %xmm0 # xmm0 = mem[0],zero
vaddps %xmm0, %xmm0, %xmm0
retq
but with the fma case, we end up scalarizing:
fma_f32:
vmovsd (%rdi), %xmm1 # xmm1 = mem[0],zero
vmovshdup %xmm1, %xmm2 # xmm2 = xmm1[1,1,3,3]
vaddss %xmm1, %xmm1, %xmm1
vaddss %xmm2, %xmm2, %xmm2
vaddss %xmm0, %xmm1, %xmm0
vinsertps $16, %xmm2, %xmm0, %xmm0 # xmm0 = xmm0[0],xmm2[0],xmm0[2,3]
retq
Ideally this would be:
fma_f32:
vmovsd (%rdi), %xmm1 # xmm1 = mem[0],zero
vaddps %xmm1, %xmm1, %xmm1
vaddss %xmm0, %xmm1, %xmm1 # xmm1[0] += xmm0[0]
vmovaps %xmm1, %xmm0
retq</pre>
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