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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 - Reduction loop - missing horizontal adds"
href="https://bugs.llvm.org/show_bug.cgi?id=42947">42947</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Reduction loop - missing horizontal adds
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>Linux
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>Backend: X86
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>david.bolvansky@gmail.com
</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
</td>
</tr></table>
<p>
<div>
<pre>float Red(float* V)
{
float sum = 0.f;
for (int I = 0; I < 4; ++I)
{
sum += V[I];
}
return sum;
}
Clang -Ofast -march=skylake -mavx2
Red(float*): # @Red(float*)
vmovupd xmm0, xmmword ptr [rdi]
vpermilpd xmm1, xmm0, 1 # xmm1 = xmm0[1,0]
vaddps xmm0, xmm0, xmm1
vmovshdup xmm1, xmm0 # xmm1 = xmm0[1,1,3,3]
vaddss xmm0, xmm0, xmm1
ret
Newest MSVC:
V$ = 8
float Red(float *) PROC ; Red, COMDAT
vmovups xmm0, XMMWORD PTR [rcx]
vhaddps xmm1, xmm0, xmm0
vhaddps xmm0, xmm1, xmm1
ret 0
float Red(float *) ENDP
Current codegen: <a href="https://godbolt.org/z/FSy0Ca">https://godbolt.org/z/FSy0Ca</a></pre>
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