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<div class="moz-cite-prefix">On 1/16/19 6:59 PM, Dmitriev, Serguei N via llvm-dev wrote:<br>
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<p class="MsoNormal"><span lang="EN-US">Hi all,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><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.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">The problem can be reproduced on the attached file as follows (many thanks to Andy Kaylor for creating this reproducer)<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">$ opt -slp-vectorizer -hotcoldsplit -slp-vectorizer -S -o - extract.ll<o:p></o:p></span></p>
<p class="MsoNormal"><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.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">...<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><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.<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><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></p>
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<p>I don't, on first impression, have a better idea.<br>
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<p class="MsoNormal"><span lang="EN-US"><o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><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></p>
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<p>I don't think that our current ValueHandle callbacks will give us this functionality. We'd need a new callback?</p>
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<p>Thanks again,</p>
<p>Hal<br>
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<p class="MsoNormal"><span lang="EN-US"><o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US"><o:p> </o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Thanks,<o:p></o:p></span></p>
<p class="MsoNormal"><span lang="EN-US">Sergey<o:p></o:p></span></p>
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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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