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<base href="https://llvm.org/bugs/" />
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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - [X86][AVX] Calling vzeroall or vzeroupper causes a second vzeroupper to be emitted"
href="https://llvm.org/bugs/show_bug.cgi?id=27823">27823</a>
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<th>Summary</th>
<td>[X86][AVX] Calling vzeroall or vzeroupper causes a second vzeroupper to be emitted
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
<tr>
<th>Version</th>
<td>trunk
</td>
</tr>
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<th>Hardware</th>
<td>PC
</td>
</tr>
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<th>OS</th>
<td>Windows NT
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
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<th>Severity</th>
<td>normal
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
</tr>
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<th>Component</th>
<td>Backend: X86
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedbugs@nondot.org
</td>
</tr>
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<th>Reporter</th>
<td>llvm-dev@redking.me.uk
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org, spatel+llvm@rotateright.com
</td>
</tr>
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<th>Classification</th>
<td>Unclassified
</td>
</tr></table>
<p>
<div>
<pre>The second vzeroupper is completely superfluous (and incredibly expensive) in
both cases:
define void @test_mm256_zeroall() {
; X32-LABEL: test_mm256_zeroall:
; X32: # BB#0:
; X32-NEXT: vzeroall
; X32-NEXT: vzeroupper
; X32-NEXT: retl
;
; X64-LABEL: test_mm256_zeroall:
; X64: # BB#0:
; X64-NEXT: vzeroall
; X64-NEXT: vzeroupper
; X64-NEXT: retq
call void @llvm.x86.avx.vzeroall()
ret void
}
declare void @llvm.x86.avx.vzeroall() nounwind readnone
define void @test_mm256_zeroupper() {
; X32-LABEL: test_mm256_zeroupper:
; X32: # BB#0:
; X32-NEXT: vzeroupper
; X32-NEXT: vzeroupper
; X32-NEXT: retl
;
; X64-LABEL: test_mm256_zeroupper:
; X64: # BB#0:
; X64-NEXT: vzeroupper
; X64-NEXT: vzeroupper
; X64-NEXT: retq
call void @llvm.x86.avx.vzeroupper()
ret void
}
declare void @llvm.x86.avx.vzeroupper() nounwind readnone</pre>
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