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<body><span class="vcard"><a class="email" href="mailto:spatel+llvm@rotateright.com" title="Sanjay Patel <spatel+llvm@rotateright.com>"> <span class="fn">Sanjay Patel</span></a>
</span> changed
<a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED FIXED - [x86] Vector shift left generates sub-optimal code for shift by "select" from two constants or loop-invariant values"
href="https://bugs.llvm.org/show_bug.cgi?id=37428">bug 37428</a>
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<table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>What</th>
<th>Removed</th>
<th>Added</th>
</tr>
<tr>
<td style="text-align:right;">Resolution</td>
<td>---
</td>
<td>FIXED
</td>
</tr>
<tr>
<td style="text-align:right;">Fixed By Commit(s)</td>
<td>
</td>
<td>r363511
</td>
</tr>
<tr>
<td style="text-align:right;">Status</td>
<td>NEW
</td>
<td>RESOLVED
</td>
</tr></table>
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<b><a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED FIXED - [x86] Vector shift left generates sub-optimal code for shift by "select" from two constants or loop-invariant values"
href="https://bugs.llvm.org/show_bug.cgi?id=37428#c13">Comment # 13</a>
on <a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED FIXED - [x86] Vector shift left generates sub-optimal code for shift by "select" from two constants or loop-invariant values"
href="https://bugs.llvm.org/show_bug.cgi?id=37428">bug 37428</a>
from <span class="vcard"><a class="email" href="mailto:spatel+llvm@rotateright.com" title="Sanjay Patel <spatel+llvm@rotateright.com>"> <span class="fn">Sanjay Patel</span></a>
</span></b>
<pre>I think we've solved all of the vector shift bugs in these examples with:
<a href="https://reviews.llvm.org/rL363511">https://reviews.llvm.org/rL363511</a>
...so I'm going to mark this as fixed. Feel free to reopen if I missed
anything.
AVX1 is still sub-optimal even after:
<a href="https://reviews.llvm.org/rL363508">https://reviews.llvm.org/rL363508</a>
I'll investigate that as a follow-up, but I see 2 potential symptoms depending
on the example:
1. We unrolled too much and ran out of registers, so we're spilling.
2. We failed to expand/hoist all of the vector shifts when fully unrolled.
Root cause may be cost model/unrolling. Ie, I don't see these problems if I use
"-fno-unroll-loops" (and perf improves with that setting).</pre>
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