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<body><span class="vcard"><a class="email" href="mailto:max.kazantsev@azul.com" title="Max Kazantsev <max.kazantsev@azul.com>"> <span class="fn">Max Kazantsev</span></a>
</span> changed
<a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED FIXED - [SCEV] computeBackedgeTakenCount() returns incorrect BackedgeTakenInfo"
href="https://bugs.llvm.org/show_bug.cgi?id=48225">bug 48225</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>
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<td style="text-align:right;">Status</td>
<td>NEW
</td>
<td>RESOLVED
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<p>
<div>
<b><a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED FIXED - [SCEV] computeBackedgeTakenCount() returns incorrect BackedgeTakenInfo"
href="https://bugs.llvm.org/show_bug.cgi?id=48225#c6">Comment # 6</a>
on <a class="bz_bug_link
bz_status_RESOLVED bz_closed"
title="RESOLVED FIXED - [SCEV] computeBackedgeTakenCount() returns incorrect BackedgeTakenInfo"
href="https://bugs.llvm.org/show_bug.cgi?id=48225">bug 48225</a>
from <span class="vcard"><a class="email" href="mailto:max.kazantsev@azul.com" title="Max Kazantsev <max.kazantsev@azul.com>"> <span class="fn">Max Kazantsev</span></a>
</span></b>
<pre>Fix merged.
commit 48d7cc6ae23b0e5b1922457462d0f6e4582a1ae7
Author: Max Kazantsev <<a href="mailto:mkazantsev@azul.com">mkazantsev@azul.com</a>>
Date: Mon Nov 23 16:45:20 2020 +0700
[SCEV] Fix incorrect treatment of max taken count. PR48225
SCEV makes a logical mistake when handling EitherMayExit in
case when both conditions must be met to exit the loop. The
mistake looks like follows: "if condition `A` fails within at most `X`
first
iterations, and `B` fails within at most `Y` first iterations, then `A & B`
fails at most within `min (X, Y)` first iterations". This is wrong, because
both of them must fail at the same time.
Simple example illustrating this is following: we have an IV with step 1,
condition `A` = "IV is even", condition `B` = "IV is odd". Both `A` and `B`
will fail within first two iterations. But it doesn't mean that both of
them
will fail within first two first iterations at the same time, which would
mean
that IV is neither even nor odd at the same time within first 2 iterations.
We can only do so for known exact BE counts, but not for max.
Differential Revision: <a href="https://reviews.llvm.org/D91942">https://reviews.llvm.org/D91942</a>
Reviewed By: nikic</pre>
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