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We have an interface for estimating this, although it depends on the targets providing appropriate information through the TargetTransformInfo interface.</div>
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Call TTI->getInstructionCost with the kind parameter set to TCK_Latency.</div>
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-Hal</div>
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<div class="PlainText">Hal Finkel<br>
Lead, Compiler Technology and Programming Languages<br>
Leadership Computing Facility<br>
Argonne National Laboratory</div>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" color="#000000" style="font-size:11pt"><b>From:</b> llvm-dev <llvm-dev-bounces@lists.llvm.org> on behalf of Matt Davis via llvm-dev <llvm-dev@lists.llvm.org><br>
<b>Sent:</b> Monday, May 13, 2019 10:04 AM<br>
<b>To:</b> Duan Bing; LLVM Developers Mailing List<br>
<b>Subject:</b> Re: [llvm-dev] How shall I evaluate the latency of each instruction in LLVM IR?</font>
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Hi Duan,</p>
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It sounds like you might be interested in llvm’s Machine Code Analyzer. It’s an llvm tool that can calculate reciprocal throughput by simulating an out-of-order instruction pipeline. It also provides other useful cycle information:</p>
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<a href="https://llvm.org/docs/CommandGuide/llvm-mca.html">https://llvm.org/docs/CommandGuide/llvm-mca.html</a></p>
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Your question asks about IR. llvm-mca currently only works on assembly. However, you can easily generate assembly from IR or make use of MCA as a library. I suggest just converting your IR to assembly and running that through llvm-mca.</p>
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MCA is built on LLVM instruction scheduling information which contains cycle latency information. If you’re curious of what that data looks like, outside of MCA, take a peek at the X86 instruction scheduling information located around: ‘llvm/lib/Target/X86/X86Schedule.td’</p>
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-Matt</p>
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<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 Duan Bing via llvm-dev <llvm-dev@lists.llvm.org><br>
<b>Reply-To: </b>Duan Bing <hibduan@gmail.com><br>
<b>Date: </b>Sunday, May 12, 2019 at 6:59 PM<br>
<b>To: </b>LLVM Developers Mailing List <llvm-dev@lists.llvm.org><br>
<b>Subject: </b>[llvm-dev] How shall I evaluate the latency of each instruction in LLVM IR?</span></p>
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Inspired by <a href="https://urldefense.proofpoint.com/v2/url?u=https-3A__www.agner.org_optimize_instruction-5Ftables.pdf&d=DwMFaQ&c=5VD0RTtNlTh3ycd41b3MUw&r=UilupKr8sbkenSLlythLNg&m=DWhb3uSjfkI09NsIvzdD_gqnlaI7VN0NpDYUdEvguDw&s=g7xcpplySDXjLzySPYQQjj3BbmDZdSgQtcKxwgCOh9s&e=">https://www.agner.org/optimize/instruction_tables.pdf</a>,
which gives us the latency and reciprocal throughput of each instruction in the different architecture of X86, Is there anybody taking the effort to do a similar job for LLVM IR?
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Thanks!</p>
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