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<div class="moz-cite-prefix">On 1/17/19 11:19 AM, Dmitriev, Serguei N wrote:<br>
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<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US">Hi Hal,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US"><o:p> </o:p></span></p>
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<p class="MsoNormal" style="text-indent:35.4pt"><span lang="EN-US">On 1/16/19 6:59 PM, Dmitriev, Serguei N via llvm-dev wrote:<o:p></o:p></span></p>
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<p class="MsoNormal" style="margin-left:34.8pt"><span lang="EN-US">Hi all,</span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:34.8pt"><span lang="EN-US"> </span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:34.8pt"><span lang="EN-US">We have recently encountered a problem with AssumptionCache that it does not get updated when a block with llvm.assume calls gets outlined by the CodeExtractor. As a result we end up with stale
references to the llvm.assume calls that were moved to the outlined function in the parent function’s cache.</span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:34.8pt"><span lang="EN-US"> </span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:34.8pt"><span lang="EN-US">The problem can be reproduced on the attached file as follows (many thanks to Andy Kaylor for creating this reproducer)</span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:34.8pt"><span lang="EN-US"> </span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:34.8pt"><span lang="EN-US">$ opt -slp-vectorizer -hotcoldsplit -slp-vectorizer -S -o - extract.ll</span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:34.8pt"><span lang="EN-US">opt: .../llvm/lib/Analysis/CodeMetrics.cpp:107: static void llvm::CodeMetrics::collectEphemeralValues(const llvm::Function*, llvm::AssumptionCache*, llvm::SmallPtrSetImpl<const llvm::Value*>&):
Assertion `I->getParent()->getParent() == F && "Found assumption for the wrong function!"' failed.</span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:34.8pt"><span lang="EN-US">...</span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:34.8pt"><span lang="EN-US"> </span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:34.8pt"><span lang="EN-US">The comments in the AssumptionCache seem to indicate that we should never get into this situation because AssumptionCache is supposed to be self-updating, but the case when a block with llvm.assume
call is moved from one function to another is not correctly handled now. I wonder what the right way to fix this problem is.</span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:34.8pt"><span lang="EN-US"> </span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:34.8pt"><span lang="EN-US">I guess a straightforward solution would be just changing CodeExtractor to clear function’s assumption cache right after extracting blocks from it, but that would require adding assumption analysis
as a dependency to every pass that uses CodeExtractor.</span><o:p></o:p></p>
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<p style="margin-left:34.8pt"><o:p> </o:p></p>
<p style="margin-left:34.8pt">I don't, on first impression, have a better idea.<o:p></o:p></p>
<p style="margin-left:34.8pt"><span style="color:windowtext"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US">Ok, I will probably implement this solution so far.</span><span style="color:windowtext" lang="EN-US"><o:p></o:p></span></p>
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<p class="MsoNormal" style="margin-left:34.8pt"><span lang="EN-US"> <o:p></o:p></span></p>
<p class="MsoNormal" style="margin-left:34.8pt"><span lang="EN-US">Or maybe there could be other solutions like for example somehow extending callback mechanism to handle updates of the basic block parent. Can you please suggest any ideas?</span><o:p></o:p></p>
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<p style="margin-left:34.8pt"><o:p> </o:p></p>
<p style="margin-left:34.8pt">I don't think that our current ValueHandle callbacks will give us this functionality. We'd need a new callback?<o:p></o:p></p>
<p style="margin-left:34.8pt"><span style="color:windowtext"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US">I also think that existing callbacks cannot handle the case when block’s parent is changed, so something new will be needed. AssumptionCache as I understand was designed to be self-updating, so maybe
it would be nice to maintain this property.</span></p>
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<p>I agree. Unfortunately, when writing the code I didn't think about this use case. Also, we need to weigh the cost of adding the callback vs. updating the more-rare transformation code. If the callback would appear on an otherwise hot path, it might not be
the right trade off.</p>
<p> -Hal<br>
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<p><br>
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<blockquote type="cite" cite="mid:1112AE43C04F2E428633A4D42126DB32ACBCE7E8@ORSMSX111.amr.corp.intel.com">
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<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D" lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:RU" lang="EN-US">Thanks,<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D;mso-fareast-language:RU" lang="EN-US">Sergey<o:p></o:p></span></p>
<p class="MsoNormal"><span style="color:windowtext"><o:p> </o:p></span></p>
<p style="margin-left:34.8pt">Thanks again,<o:p></o:p></p>
<p style="margin-left:34.8pt">Hal<o:p></o:p></p>
<p style="margin-left:34.8pt"><o:p> </o:p></p>
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<p class="MsoNormal" style="margin-left:34.8pt"><span lang="EN-US"> </span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:34.8pt"><span lang="EN-US">Thanks,</span><o:p></o:p></p>
<p class="MsoNormal" style="margin-left:34.8pt"><span lang="EN-US">Sergey</span><o:p></o:p></p>
<p class="MsoNormal"><span style="font-size:12.0pt;font-family:"Times New
Roman",serif;mso-fareast-language:RU"><br>
<br>
<o:p></o:p></span></p>
<pre>_______________________________________________<o:p></o:p></pre>
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<pre>-- <o:p></o:p></pre>
<pre>Hal Finkel<o:p></o:p></pre>
<pre>Lead, Compiler Technology and Programming Languages<o:p></o:p></pre>
<pre>Leadership Computing Facility<o:p></o:p></pre>
<pre>Argonne National Laboratory<o:p></o:p></pre>
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<pre class="moz-signature" cols="72">--
Hal Finkel
Lead, Compiler Technology and Programming Languages
Leadership Computing Facility
Argonne National Laboratory</pre>
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