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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 - [llvm-exegesis] Instructions should avoid tied registers (BLENDVPD/BLENDVPS/PBLENDVB etc.)"
href="https://bugs.llvm.org/show_bug.cgi?id=39159">39159</a>
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<th>Summary</th>
<td>[llvm-exegesis] Instructions should avoid tied registers (BLENDVPD/BLENDVPS/PBLENDVB etc.)
</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>Windows NT
</td>
</tr>
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<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</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>
<tr>
<th>Reporter</th>
<td>llvm-dev@redking.me.uk
</td>
</tr>
<tr>
<th>CC</th>
<td>andrea.dibiagio@gmail.com, clement.courbet@gmail.com, gchatelet@google.com, llvm-bugs@lists.llvm.org
</td>
</tr></table>
<p>
<div>
<pre>BLENDVPD/BLENDVPS/PBLENDVB use xmm0 as the mask src register, but
llvm-exegesis's uop computation uses this register both as a src and dst,
resulting in spurious results (extra uop counts, stalls etc.)
mode: uops
key:
instructions:
- 'BLENDVPDrm0 XMM0 XMM0 RDI i_0x1x i_0x0x '
- 'BLENDVPDrm0 XMM1 XMM1 RDI i_0x1x i_0x64x '
- 'BLENDVPDrm0 XMM2 XMM2 RDI i_0x1x i_0x128x '
- 'BLENDVPDrm0 XMM3 XMM3 RDI i_0x1x i_0x192x '
- 'BLENDVPDrm0 XMM4 XMM4 RDI i_0x1x i_0x256x '
- 'BLENDVPDrm0 XMM5 XMM5 RDI i_0x1x i_0x320x '
- 'BLENDVPDrm0 XMM6 XMM6 RDI i_0x1x i_0x384x '
- 'BLENDVPDrm0 XMM7 XMM7 RDI i_0x1x i_0x448x '
- 'BLENDVPDrm0 XMM8 XMM8 RDI i_0x1x i_0x512x '
- 'BLENDVPDrm0 XMM9 XMM9 RDI i_0x1x i_0x576x '
- 'BLENDVPDrm0 XMM10 XMM10 RDI i_0x1x i_0x640x '
- 'BLENDVPDrm0 XMM11 XMM11 RDI i_0x1x i_0x704x '
- 'BLENDVPDrm0 XMM12 XMM12 RDI i_0x1x i_0x768x '
- 'BLENDVPDrm0 XMM13 XMM13 RDI i_0x1x i_0x832x '
- 'BLENDVPDrm0 XMM14 XMM14 RDI i_0x1x i_0x896x '
- 'BLENDVPDrm0 XMM15 XMM15 RDI i_0x1x i_0x960x '
config: ''
register_initial_values:
- 'XMM0=0x0'
- 'XMM1=0x0'
- 'XMM2=0x0'
- 'XMM3=0x0'
- 'XMM4=0x0'
- 'XMM5=0x0'
- 'XMM6=0x0'
- 'XMM7=0x0'
- 'XMM8=0x0'
- 'XMM9=0x0'
- 'XMM10=0x0'
- 'XMM11=0x0'
- 'XMM12=0x0'
- 'XMM13=0x0'
- 'XMM14=0x0'
- 'XMM15=0x0'
cpu_name: btver2
llvm_triple: x86_64-unknown-linux-gnu
num_repetitions: 10000
measurements:
- { debug_string: JFPU0, value: 1.47, per_snippet_value: 23.52, key: JFPU0 }
- { debug_string: JFPU1, value: 1.5349, per_snippet_value: 24.5584, key:
JFPU1 }
- { debug_string: NumMicroOps, value: 4.0158, per_snippet_value: 64.2528,
key: NumMicroOps }</pre>
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