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<p class="MsoNormal">Hi Lorenzo,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I’ll answer the first question you have:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span style="font-family:"Helvetica Neue"">> I would like to use llvm-mca to estimate the IPC of a given code region. I am interested in the library version (<a href="https://urldefense.proofpoint.com/v2/url?u=https-3A__reviews.llvm.org_D50929-3Fid-3D162210&d=DwMFAg&c=5VD0RTtNlTh3ycd41b3MUw&r=o3kDXzdBUE3ljQXKeTWOMw&m=Ehy5cbFrTOTrtNpj4jTjwnMXspCxyoUuKpn3m8pxGpg&s=iEwPb0T8FqcGV-IscWqa3SAw64L-buGNLYvMLOgWoi4&e=">https://reviews.llvm.org/D50929?id=162210</a>)
 but I have troubles understanding how to use it. Could you please point me to some documentations or (better) some code examples if any?</span><o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">The best example of the llvm-mca library being used is the actual llvm-mca tool itself.  If you look in llvm/tools/llvm-mca/llvm-mca.cpp you’ll see that it is just a large program that uses the llvm-mca API and library.  You’ll want to
 look at main() where the default pipline is created and the viewers are associated to that pipeline instance.<o:p></o:p></p>
<ol style="margin-top:0in" start="1" type="1">
<li class="MsoListParagraph" style="margin-left:0in;mso-list:l1 level1 lfo2">You’ll need to construct an mca::Context and use that to create a mca::Pipeline instance.  For starters, I suggest just using the default “out-of-order” pipeline.  “createDefaultPipeline”<o:p></o:p></li><li class="MsoListParagraph" style="margin-left:0in;mso-list:l1 level1 lfo2">Next, register some handlers take a look at the HWEventListener class in include/llvm/MCA.  Use “Pipeline::addEventListener” to register for the events you might be interested in,
 such as pipeline stalls.<o:p></o:p></li></ol>
<p class="MsoNormal" style="margin-left:.5in">llvm-mca.cpp does this on behalf of the Viewers.  If you trace what the viewers are doing in the source file, you’ll probably<o:p></o:p></p>
<p class="MsoNormal" style="margin-left:.5in">want to do something similar. <o:p>
</o:p></p>
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<li class="MsoListParagraph" style="margin-left:0in;mso-list:l1 level1 lfo2">Call “Pipeline::run” to start your experiment and collect performance information.<o:p></o:p></li></ol>
<p class="MsoListParagraph"><o:p> </o:p></p>
<p class="MsoNormal">Your second question:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span style="font-family:"Helvetica Neue"">> Reading the documentation (<a href="https://urldefense.proofpoint.com/v2/url?u=https-3A__llvm.org_docs_CommandGuide_llvm-2Dmca.html&d=DwMFAg&c=5VD0RTtNlTh3ycd41b3MUw&r=o3kDXzdBUE3ljQXKeTWOMw&m=Ehy5cbFrTOTrtNpj4jTjwnMXspCxyoUuKpn3m8pxGpg&s=5845DcPA4uSN_lgPE_SlH6XwRSShIfPIvYR1t8AZHpU&e=">https://llvm.org/docs/CommandGuide/llvm-mca.html</a>)
 it also seems that llvm-mca does not take into account the cache hierarchy. Does this mean that the tool assumes all the loads/stores hit the L1 cache?</span><o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">As you pointed out, MCA does not really model the cache hierarchy.  You might want to take a look at the Load/Store unit documentation as well:
<a href="http://llvm.org/doxygen/classllvm_1_1mca_1_1LSUnit.html">http://llvm.org/doxygen/classllvm_1_1mca_1_1LSUnit.html</a><o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">You probably already saw this from the CommandGuide for llvm-mca, but I’ll repeat it here:<o:p></o:p></p>
<p class="MsoNormal">“The LSUnit does not attempt to predict if a load or store hits or misses the L1 cache. It only knows if an instruction “MayLoad” and/or “MayStore.” For loads, the scheduling model provides an “optimistic” load-to-use latency (which usually
 matches the load-to-use latency for when there is a hit in the L1D).”<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Hope that helps,<o:p></o:p></p>
<p class="MsoNormal">-Matt<o:p></o:p></p>
<p class="MsoListParagraph" style="margin-left:0in"><span style="font-size:10.5pt;font-family:"Lucida Grande",sans-serif;color:black;background:white"><o:p> </o:p></span></p>
<p class="MsoListParagraph" style="margin-left:0in"><o:p> </o:p></p>
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<p class="MsoNormal"><b><span style="font-size:12.0pt;color:black">From: </span></b><span style="font-size:12.0pt;color:black">Shoaib Meenai <smeenai@fb.com><br>
<b>Date: </b>Thursday, May 2, 2019 at 11:34 AM<br>
<b>To: </b>lorenzo chelini <l.chelini@icloud.com>, "llvm-dev@lists.llvm.org" <llvm-dev@lists.llvm.org>, Matt Davis <nullptr@fb.com><br>
<b>Subject: </b>Re: [llvm-dev] Llvm-mca library.<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal">(Adding Matt Davis, who should be able to help out here.)<o:p></o:p></p>
<p class="MsoNormal"> <o:p></o:p></p>
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<p class="MsoNormal"><b><span style="font-size:12.0pt;color:black">From: </span></b><span style="font-size:12.0pt;color:black">llvm-dev <llvm-dev-bounces@lists.llvm.org> on behalf of lorenzo chelini via llvm-dev <llvm-dev@lists.llvm.org><br>
<b>Reply-To: </b>lorenzo chelini <l.chelini@icloud.com><br>
<b>Date: </b>Thursday, May 2, 2019 at 4:15 AM<br>
<b>To: </b>"llvm-dev@lists.llvm.org" <llvm-dev@lists.llvm.org><br>
<b>Subject: </b>[llvm-dev] Llvm-mca library.</span><o:p></o:p></p>
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<p class="MsoNormal"> <o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Helvetica Neue"">Hi All,</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Helvetica Neue""> </span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Helvetica Neue"">I would like to use llvm-mca to estimate the IPC of a given code region. I am interested in the library version (<a href="https://urldefense.proofpoint.com/v2/url?u=https-3A__reviews.llvm.org_D50929-3Fid-3D162210&d=DwMFAg&c=5VD0RTtNlTh3ycd41b3MUw&r=o3kDXzdBUE3ljQXKeTWOMw&m=Ehy5cbFrTOTrtNpj4jTjwnMXspCxyoUuKpn3m8pxGpg&s=iEwPb0T8FqcGV-IscWqa3SAw64L-buGNLYvMLOgWoi4&e=">https://reviews.llvm.org/D50929?id=162210</a>)
 but I have troubles understanding how to use it. Could you please point me to some documentations or (better) some code examples if any?</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Helvetica Neue""> </span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Helvetica Neue"">Reading the documentation (<a href="https://urldefense.proofpoint.com/v2/url?u=https-3A__llvm.org_docs_CommandGuide_llvm-2Dmca.html&d=DwMFAg&c=5VD0RTtNlTh3ycd41b3MUw&r=o3kDXzdBUE3ljQXKeTWOMw&m=Ehy5cbFrTOTrtNpj4jTjwnMXspCxyoUuKpn3m8pxGpg&s=5845DcPA4uSN_lgPE_SlH6XwRSShIfPIvYR1t8AZHpU&e=">https://llvm.org/docs/CommandGuide/llvm-mca.html</a>)
 it also seems that llvm-mca does not take into account the cache hierarchy. Does this mean that the tool assumes all the loads/stores hit the L1 cache?</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Helvetica Neue""> </span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Helvetica Neue"">Looking forward to hearing from you.</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Helvetica Neue"">Best regards,</span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Helvetica Neue""> </span><o:p></o:p></p>
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<p class="MsoNormal"><span style="font-family:"Helvetica Neue"">Lorenzo Chelini.</span><o:p></o:p></p>
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