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<base href="https://bugs.freedesktop.org/" />
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<body><table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>Priority</th>
<td>medium
</td>
</tr>
<tr>
<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW --- - i965/fs generates slow code for vector comparisons"
href="https://bugs.freedesktop.org/show_bug.cgi?id=77456">77456</a>
</td>
</tr>
<tr>
<th>Assignee</th>
<td>idr@freedesktop.org
</td>
</tr>
<tr>
<th>Summary</th>
<td>i965/fs generates slow code for vector comparisons
</td>
</tr>
<tr>
<th>QA Contact</th>
<td>intel-3d-bugs@lists.freedesktop.org
</td>
</tr>
<tr>
<th>Severity</th>
<td>normal
</td>
</tr>
<tr>
<th>Classification</th>
<td>Unclassified
</td>
</tr>
<tr>
<th>OS</th>
<td>All
</td>
</tr>
<tr>
<th>Reporter</th>
<td>mattst88@gmail.com
</td>
</tr>
<tr>
<th>Hardware</th>
<td>Other
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Version</th>
<td>unspecified
</td>
</tr>
<tr>
<th>Component</th>
<td>glsl-compiler
</td>
</tr>
<tr>
<th>Product</th>
<td>Mesa
</td>
</tr></table>
<p>
<div>
<pre>Created <span class=""><a href="attachment.cgi?id=97371" name="attach_97371" title="t.shader_test">attachment 97371</a> <a href="attachment.cgi?id=97371&action=edit" title="t.shader_test">[details]</a></span>
t.shader_test
The fragment shader runs in scalar mode, so to do vec4 comparisons we generate
multiple compares and join them together using and or ors, depending on the
comparison.
INTEL_DEBUG=fs,no16 bin/shader_runner t.shader_test -auto
generates:
cmp.e.f0(8) g3<1>D g2.3<0,1,0>F g2.7<0,1,0>F
cmp.e.f0(8) g4<1>D g2.2<0,1,0>F g2.6<0,1,0>F
cmp.e.f0(8) g5<1>D g2.1<0,1,0>F g2.5<0,1,0>F
cmp.e.f0(8) g6<1>D g2<0,1,0>F g2.4<0,1,0>F
and(8) g7<1>D g5<8,8,1>D g6<8,8,1>D
and(8) g8<1>D g4<8,8,1>D g7<8,8,1>D
and(8) g9<1>D g3<8,8,1>D g8<8,8,1>D
and.ne.f0(8) null g9<8,8,1>D 1D
...
(+f0) sel ...
We could have just predicated all but the first cmp instruction and skipped the
and instructions completely:
cmp.e.f0(8) g3<1>D g2.3<0,1,0>F g2.7<0,1,0>F
(+f0) cmp.e.f0(8) g4<1>D g2.2<0,1,0>F g2.6<0,1,0>F
(+f0) cmp.e.f0(8) g5<1>D g2.1<0,1,0>F g2.5<0,1,0>F
(+f0) cmp.e.f0(8) g6<1>D g2<0,1,0>F g2.4<0,1,0>F
...
(+f0) sel ...
I think a similar thing can be done for !=, where the join operation is or.</pre>
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