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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 - [SLP] Allow sequential fadd reductions"
href="https://bugs.llvm.org/show_bug.cgi?id=51246">51246</a>
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<th>Summary</th>
<td>[SLP] Allow sequential fadd reductions
</td>
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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
</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, david.green@arm.com, david.sherwood@arm.com, llvm-bugs@lists.llvm.org, sander.desmalen@arm.com, spatel+llvm@rotateright.com
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<div>
<pre>define double @dot4f64(double* %ptrx, double* %ptry) {
%ptrx1 = getelementptr inbounds double, double* %ptrx, i64 1
%ptry1 = getelementptr inbounds double, double* %ptry, i64 1
%ptrx2 = getelementptr inbounds double, double* %ptrx, i64 2
%ptry2 = getelementptr inbounds double, double* %ptry, i64 2
%ptrx3 = getelementptr inbounds double, double* %ptrx, i64 3
%ptry3 = getelementptr inbounds double, double* %ptry, i64 3
%x0 = load double, double* %ptrx, align 8
%y0 = load double, double* %ptry, align 8
%x1 = load double, double* %ptrx1, align 8
%y1 = load double, double* %ptry1, align 8
%x2 = load double, double* %ptrx2, align 8
%y2 = load double, double* %ptry2, align 8
%x3 = load double, double* %ptrx3, align 8
%y3 = load double, double* %ptry3, align 8
%mul0 = fmul double %x0, %y0
%mul1 = fmul double %x1, %y1
%mul2 = fmul double %x2, %y2
%mul3 = fmul double %x3, %y3
%dot01 = fadd double %mul0, %mul1
%dot012 = fadd double %dot01, %mul2
%dot0123 = fadd double %dot012, %mul3
ret double %dot0123
}
At least on AVX targets, this (non-fast) dot product would still benefit from
vectorizing the multiplication and then performing a sequential/unordered fadd
reduction - but SLP currently limits reductions to associative ops.</pre>
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