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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - LLVM too aggressive about using vector ctpop"
href="https://bugs.llvm.org/show_bug.cgi?id=47825">47825</a>
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<th>Summary</th>
<td>LLVM too aggressive about using vector ctpop
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<th>Product</th>
<td>libraries
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<th>Version</th>
<td>trunk
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<th>Hardware</th>
<td>PC
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<th>OS</th>
<td>All
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<th>Status</th>
<td>NEW
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<th>Severity</th>
<td>normal
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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>dave@znu.io
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<th>CC</th>
<td>craig.topper@gmail.com, llvm-bugs@lists.llvm.org, llvm-dev@redking.me.uk, pengfei.wang@intel.com, spatel+llvm@rotateright.com
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<pre>The following code generates quite sub-optimal assembly on targets that don't
have a vector population count instruction:
__mmask8 popCountLessThanOrEqualToOne(__m512i value) {
return _mm512_testn_epi64_mask(value, value - 1);
}
It seems like the generic optimization pass(es) are converting this into a
vector "ctpop" without checking whether the back end has the instruction or
not. Whoops.</pre>
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