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<div class="moz-cite-prefix">On 6/19/16 4:28 AM, Mehdi Amini via
llvm-dev wrote:<br>
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<blockquote
cite="mid:0232184D-03EA-44D4-B689-2A7FB1BFCA4E@apple.com"
type="cite">
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<div class="">On Jun 18, 2016, at 10:44 PM, Yuxi Chen via
llvm-dev <<a moz-do-not-send="true"
href="mailto:llvm-dev@lists.llvm.org" class="">llvm-dev@lists.llvm.org</a>>
wrote:</div>
<br class="Apple-interchange-newline">
<div class="">
<div class="">Hi All,
<div class=""><br class="">
</div>
<div class="">When I use llvm, I encounter a problem like
"unable to schedule pass A required by C"</div>
<div class="">I investigated deeper. It's like:</div>
<div class="">I have three passes, say A, B, C(all are on
function level)</div>
<div class="">A would modify IR code. (change instruction
order)</div>
<div class=""><br class="">
</div>
<div class="">For pass B, </div>
<div class="">I would use the result of pass A, I use
addRequired<B>(), and &getAnalysis<B>(),
it works. </div>
<div class=""><br class="">
</div>
<div class="">void getAnalysisUsage(AU){</div>
<div class=""><span class="Apple-tab-span"></span>AU.addRequired<A>();</div>
<div class="">}</div>
<div class=""><br class="">
</div>
<div class=""><br class="">
</div>
<div class="">For pass C, it will use the results of pass
A and B. </div>
<div class="">I use the way as used for pass B, but it
failed, even for LoopInfo analysis pass(which is the
built-in analysis pass).</div>
<div class="">void getAnalysisUsage(AU){</div>
<div class=""><span class=""><span class="Apple-tab-span"></span>AU.addRequired<A>();</span></div>
<div class=""><span class=""><span class="Apple-tab-span"></span>AU.addRequired<B>();</span></div>
<div class=""><span class="">}</span></div>
<div class=""><br class="">
</div>
<div class=""><br class="">
</div>
<div class="">It seems because A would modify IR code, so
for pass C, I need first load pass A then pass B,
otherwise it will be invalidated. </div>
<div class="">However, when I change the using order, I
still got error "unable to schedule pass A required by
C".</div>
<div class=""><br class="">
</div>
<div class="">Does anyone encounter the same problem
before and have a solution?</div>
</div>
</div>
</blockquote>
<blockquote type="cite" class="">
<div class="">
<div class="">
<div class="">Any help is appreciated. </div>
</div>
</div>
</blockquote>
<div><br class="">
</div>
<div>Depending on other transformations isn’t recommended, and
isn’t supported by the soon-new-passmanager I believe.</div>
<div>The expectation is that the passes are added in order to
the pass manager by the client.</div>
</div>
</blockquote>
<br>
Depending on transformation passes isn't supported by the legacy
PassManager, either. Occasionally some passes can get away with it,
but it often results in unschedule-able pass pipelines as above.<br>
<br>
If your transform pass does something to the code, other passes
should either infer what it did by examining the IR. the IR
contains the definitive information about the program (because it is
the program).<br>
<br>
Alternatively, you could create an analysis pass upon which both
your transform and analysis passes depend. The transform pass would
update this new analysis pass with information on what it
transformed; your later analysis passes could then query this
information. This approach is fragile, but it could work.<br>
<br>
Regards,<br>
<br>
John Criswell<br>
<br>
<blockquote
cite="mid:0232184D-03EA-44D4-B689-2A7FB1BFCA4E@apple.com"
type="cite">
<div>
<div><br class="">
</div>
<div>In you case, I expect that it would “work” by removing the
dependency from C to A. If C requires B and B requires A, by
scheduling C you’ll get A, B, C in sequence.</div>
<div><br class="">
</div>
<div>— </div>
<div>Mehdi</div>
<div><br class="">
</div>
<div><br class="">
</div>
<br class="">
<blockquote type="cite" class="">
<div class="">
<div class="">
<div class=""><br class="">
</div>
<div class="">Best,</div>
<div class="">Yuxi</div>
</div>
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<br>
<p><br>
</p>
<pre class="moz-signature" cols="72">--
John Criswell
Assistant Professor
Department of Computer Science, University of Rochester
<a class="moz-txt-link-freetext" href="http://www.cs.rochester.edu/u/criswell">http://www.cs.rochester.edu/u/criswell</a></pre>
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