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<body><span class="vcard"><a class="email" href="mailto:lebedev.ri@gmail.com" title="Roman Lebedev <lebedev.ri@gmail.com>"> <span class="fn">Roman Lebedev</span></a>
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<a class="bz_bug_link
bz_status_REOPENED "
title="REOPENED - [InstCombine] Dropping pointless masking before left shift"
href="https://bugs.llvm.org/show_bug.cgi?id=42563">bug 42563</a>
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<th>What</th>
<th>Removed</th>
<th>Added</th>
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<td style="text-align:right;">Status</td>
<td>RESOLVED
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<td>REOPENED
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<td style="text-align:right;">Resolution</td>
<td>FIXED
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<td>---
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<b><a class="bz_bug_link
bz_status_REOPENED "
title="REOPENED - [InstCombine] Dropping pointless masking before left shift"
href="https://bugs.llvm.org/show_bug.cgi?id=42563#c4">Comment # 4</a>
on <a class="bz_bug_link
bz_status_REOPENED "
title="REOPENED - [InstCombine] Dropping pointless masking before left shift"
href="https://bugs.llvm.org/show_bug.cgi?id=42563">bug 42563</a>
from <span class="vcard"><a class="email" href="mailto:lebedev.ri@gmail.com" title="Roman Lebedev <lebedev.ri@gmail.com>"> <span class="fn">Roman Lebedev</span></a>
</span></b>
<pre>Actually, i'm missing the point here.
While indeed if the mask does not touch any bits that will remain
after the shift means we can drop the mask, we still can trivially do
the fold if it *does* touch some bits - that legality check also tells
us how many high bits to clear.
<a href="https://rise4fun.com/Alive/x2Cq">https://rise4fun.com/Alive/x2Cq</a>
Obviously, that won't work if we had `ashr`.
The mask is constant, so we only need one extra instruction.
I guess that means the input to `%r` needs to be one-use (or %x a constant.)</pre>
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