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<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Vector shift misoptimized with AVX512"
href="https://bugs.llvm.org/show_bug.cgi?id=35977">35977</a>
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<th>Summary</th>
<td>Vector shift misoptimized with AVX512
</td>
</tr>
<tr>
<th>Product</th>
<td>libraries
</td>
</tr>
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<th>Version</th>
<td>trunk
</td>
</tr>
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<th>Hardware</th>
<td>PC
</td>
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<th>OS</th>
<td>All
</td>
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<th>Status</th>
<td>NEW
</td>
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<th>Severity</th>
<td>normal
</td>
</tr>
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<th>Priority</th>
<td>P
</td>
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<th>Component</th>
<td>Backend: X86
</td>
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<th>Assignee</th>
<td>unassignedbugs@nondot.org
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</tr>
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<th>Reporter</th>
<td>benny.kra@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org, llvm-dev@redking.me.uk
</td>
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<p>
<div>
<pre>Created <span class=""><a href="attachment.cgi?id=19688" name="attach_19688" title="IR test case">attachment 19688</a> <a href="attachment.cgi?id=19688&action=edit" title="IR test case">[details]</a></span>
IR test case
The attached testcase (reduced from llvmpipe) is erroneously optimized away
when AVX512 is enabled.
$ llc -mcpu=skylake < t.ll
test: # @test
.cfi_startproc
# %bb.0: # %entry
vmovq (%rdi), %xmm0 # xmm0 = mem[0],zero
vpxor %xmm1, %xmm1, %xmm1
vpunpcklbw %xmm0, %xmm1, %xmm0 # xmm0 =
xmm1[0],xmm0[0],xmm1[1],xmm0[1],xmm1[2],xmm0[2],xmm1[3],xmm0[3],xmm1[4],xmm0[4],xmm1[5],xmm0[5],xmm1[6],xmm0[6],xmm1[7],xmm0[7]
vmovdqa %xmm0, (%rsi)
retq
$ llc -mcpu=skylake-avx512 < t.ll
test: # @test
vxorps %xmm0, %xmm0, %xmm0
vmovaps %xmm0, (%rsi)
retq
This seems to have started with r321085, but seems like an unrelated latent bug
in shuffle lowering.</pre>
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