<html><body><p><font size="2">Passes implemented as a loop pass can still be good for this change.</font><br><font size="2">I am referring to passes implemented as a loop pass and used as a loop pass in a loop pipeline </font><b><font size="2">may </font></b><font size="2">not be a good candidate.</font><br><font size="2">Take the LoopFullUnrollPass as an example, LoopFullUnrollPass is added in LPM2 with other loop passes, e.g. LoopIdiomRecognizePass, IndVarSimplifyPass, ...</font><br><font size="2">Loops are processed from inner to outer loop, where each loop is processed by all the passes in LPM2, before process its outer loops.</font><br><font size="2">If we change LoopFullUnrollPass to a LoopNest pass, then there is no way we can preserve the same order of processing loops.</font><br><font size="2">It </font><b><font size="2">may </font></b><font size="2">still be good to change such passes, but there can be huge performance impact, which we need to analyze and handle, and probably not the best choice to look at first.</font><br><br><font size="2">```</font><br><a href="https://llvm.org/doxygen/classllvm_1_1PassManager_3_01Loop_00_01LoopAnalysisManager_00_01LoopStandardAnalysisResults_01_6_00_01LPMUpdater_01_6_01_4.html"><font color="#4665A2">LoopPassManager</font></a> LPM2(DebugLogging);<br><br>LPM2.addPass(<a href="https://llvm.org/doxygen/classllvm_1_1LoopIdiomRecognizePass.html"><font color="#4665A2">LoopIdiomRecognizePass</font></a>());<br>LPM2.addPass(<a href="https://llvm.org/doxygen/classllvm_1_1IndVarSimplifyPass.html"><font color="#4665A2">IndVarSimplifyPass</font></a>());<br><br><font color="#E08000">for</font> (<font color="#008000">auto</font> &<a href="https://llvm.org/doxygen/README__ALTIVEC_8txt.html#a9aacd9146afe44bf656cd664e2a88c8c"><font color="#4665A2">C</font></a> : LateLoopOptimizationsEPCallbacks)<br> <a href="https://llvm.org/doxygen/README__ALTIVEC_8txt.html#a9aacd9146afe44bf656cd664e2a88c8c"><font color="#4665A2">C</font></a>(LPM2, <a href="https://llvm.org/doxygen/namespacellvm_1_1PICLevel.html#a66ddbf1bb21f90ddc44260d1ca677b6b"><font color="#4665A2">Level</font></a>);<br><br>LPM2.addPass(<a href="https://llvm.org/doxygen/classllvm_1_1LoopDeletionPass.html"><font color="#4665A2">LoopDeletionPass</font></a>());<br><br><font color="#E08000">if</font> (<a href="https://llvm.org/doxygen/AArch64FalkorHWPFFix_8cpp.html#a780618ccf661aebc12f8d991d294c950"><font color="#4665A2">Phase</font></a> != <a href="https://llvm.org/doxygen/namespacellvm.html#a5d737fb4258bb27586a1bffd557fbb49ad94cc56b0a9155d607f2609b0f5c39d3"><font color="#4665A2">ThinOrFullLTOPhase::ThinLTOPreLink</font></a> || !PGOOpt ||<br> PGOOpt->Action != <a href="https://llvm.org/doxygen/structllvm_1_1PGOOptions.html#a13bd589bcabdfc073bac5711f76dd2b6a9cbf1cb1b0731fc75926a6930592968a"><font color="#4665A2">PGOOptions::SampleUse</font></a>)<br> LPM2.addPass(<a href="https://llvm.org/doxygen/classllvm_1_1LoopFullUnrollPass.html"><font color="#4665A2">LoopFullUnrollPass</font></a>(<a href="https://llvm.org/doxygen/namespacellvm_1_1PICLevel.html#a66ddbf1bb21f90ddc44260d1ca677b6b"><font color="#4665A2">Level</font></a>.getSpeedupLevel(),<br><font color="#800000"> /* OnlyWhenForced= */</font> !PTO.<a href="https://llvm.org/doxygen/classllvm_1_1PipelineTuningOptions.html#af5b2b612c2769e79040e34bc4be7a77f"><font color="#4665A2">LoopUnrolling</font></a>,<br> PTO.<a href="https://llvm.org/doxygen/classllvm_1_1PipelineTuningOptions.html#ac4261b710708d3ffd351693d268dbc2b"><font color="#4665A2">ForgetAllSCEVInLoopUnroll</font></a>));<br><br><font color="#E08000">for</font> (<font color="#008000">auto</font> &<a href="https://llvm.org/doxygen/README__ALTIVEC_8txt.html#a9aacd9146afe44bf656cd664e2a88c8c"><font color="#4665A2">C</font></a> : LoopOptimizerEndEPCallbacks)<br> (LPM2, <a href="https://llvm.org/doxygen/namespacellvm_1_1PICLevel.html#a66ddbf1bb21f90ddc44260d1ca677b6b"><font color="#4665A2">Level</font></a>);<br><br>FPM.<a href="https://llvm.org/doxygen/classllvm_1_1PassManager.html#a314ff184ce4ace8801e1158ef909e22e"><font color="#4665A2">addPass</font></a>(<a href="https://llvm.org/doxygen/namespacellvm.html#a5118c8cfac85abdec7366d89d023a1ef"><font color="#4665A2">createFunctionToLoopPassAdaptor</font></a>(<br> <a href="https://llvm.org/doxygen/lib_2Target_2ARM_2README_8txt.html#ad3a99906764c35b2694ae90fa57744a5"><font color="#4665A2">std::move</font></a>(LPM2), <font color="#800000">/*UseMemorySSA=*/</font><font color="#008000">false</font>, <font color="#800000">/*UseBlockFrequencyInfo=*/</font><font color="#008000">false</font>,<br> DebugLogging));<br><font size="2">```<br><br>Regards,</font><br><font size="2">Whitney Tsang</font><br><br><img width="16" height="16" src="cid:1__=8FBB0C0ADFD5287C8f9e8a93df938690918c8FB@" border="0" alt="Inactive hide details for uint256_t ---2021/03/14 08:48:39 PM---Hello, I have a question about finding good passes for utilizin"><font size="2" color="#424282">uint256_t ---2021/03/14 08:48:39 PM---Hello, I have a question about finding good passes for utilizing LoopNest pass.</font><br><br><font size="2" color="#5F5F5F">From: </font><font size="2">uint256_t <konndennsa@gmail.com></font><br><font size="2" color="#5F5F5F">To: </font><font size="2">Whitney T Tsang <whitneyt@ca.ibm.com></font><br><font size="2" color="#5F5F5F">Cc: </font><font size="2">etiotto@ca.ibm.com, llvm-dev <llvm-dev@lists.llvm.org></font><br><font size="2" color="#5F5F5F">Date: </font><font size="2">2021/03/14 08:48 PM</font><br><font size="2" color="#5F5F5F">Subject: </font><font size="2">[EXTERNAL] Re: [llvm-dev] [GSoC 2021] Utilize LoopNest Pass</font><br><hr width="100%" size="2" align="left" noshade style="color:#8091A5; "><br><br><br>Hello,<br><br>I have a question about finding good passes for utilizing LoopNest pass.<br><br>> The LoopFullUnrollPass is not a good candidate for the change, as it is a loop pass and it is being used as a loop pass.<br>Then you mean that passes which are implemented as not a loop pass (= function pass) and not already used as a loop pass are good for this change? <br>I didn't get that. Could you tell me why it is?<br><br>Thanks in advance,<br>Toshiki Maekawa<br><br>On Fri, Mar 12, 2021, 1:20 AM uint256_t <<a href="mailto:konndennsa@gmail.com"><u><font color="#0000FF">konndennsa@gmail.com</font></u></a>> wrote:
<ul>Thank you for your advice. As you mentioned, LoopUnrollAndJam seems to be a good candidate.<br>I'm going to find another analyse/transform pass suitable for loop nest pass.<br><br>Best,<br>Toshiki Maekawa<br><br>2021年3月10日(水) 23:32 Whitney T Tsang <<a href="mailto:whitneyt@ca.ibm.com" target="_blank"><u><font color="#0000FF">whitneyt@ca.ibm.com</font></u></a>>:<br><font size="2">Sure, in this project, we plan to utilize the LoopNest pass in some existing passes. <br>As an example, here is one of the patches to transform the loop interchange pass: </font><a href="https://urldefense.proofpoint.com/v2/url?u=https-3A__reviews.llvm.org_D97847&d=DwMFaQ&c=jf_iaSHvJObTbx-siA1ZOg&r=p0DGcdtx8-l1bvwJTLSk1zBTXpb78Y1slqHKTsTpRTE&m=jWroZycNsW6nd1M_1mY-ewIVdwzOlw5vCcjh1dbGSe4&s=EkAhMZOMb7Zi_Wl2c2bPJ96JVP-RJ4Pyr8TFI1w5e2g&e=" target="_blank"><u><font size="2" color="#0000FF">https://reviews.llvm.org/D97847</font></u></a><font size="2">.<br>On top of doing the code changes, we want to understand what are the pros and cons of the change.<br>We can do that by collecting some data, e.g. compile time.</font><br><font size="2"><br>There are two loop unroller, LoopFullUnrollPass and LoopUnrollPass.<br>The LoopFullUnrollPass is not a good candidate for the change, as it is a loop pass and it is being used as a loop pass.<br>It is written to be traverse from inner to outer loop, with other loop transformations in between in the loop pipeline. <br>The LoopUnrollPass could be a candidate, but the LoopUnrollAndJamPass can be an easier to understand candidate, <br>as unroll and jam transformation naturally operate on more than one loop (LoopNest).</font><br><font size="2"><br>Regards,<br>Whitney Tsang</font><br><br><img src="cid:1__=8FBB0C0ADFD5287C8f9e8a93df938690918c8FB@" width="16" height="16" alt="Inactive hide details for uint256_t ---2021/03/10 07:52:17 AM---I'm glad to get in touch with you two. I'm planning to utilize"><font size="2" color="#424282">uint256_t ---2021/03/10 07:52:17 AM---I'm glad to get in touch with you two. I'm planning to utilize LoopNest pass for some passes like lo</font><br><font size="2" color="#5F5F5F"><br>From: </font><font size="2">uint256_t <</font><a href="mailto:konndennsa@gmail.com" target="_blank"><u><font size="2" color="#0000FF">konndennsa@gmail.com</font></u></a><font size="2">></font><font size="2" color="#5F5F5F"><br>To: <br>Cc: </font><font size="2">llvm-dev <</font><a href="mailto:llvm-dev@lists.llvm.org" target="_blank"><u><font size="2" color="#0000FF">llvm-dev@lists.llvm.org</font></u></a><font size="2">>, </font><a href="mailto:etiotto@ca.ibm.com" target="_blank"><u><font size="2" color="#0000FF">etiotto@ca.ibm.com</font></u></a><font size="2">, </font><a href="mailto:whitneyt@ca.ibm.com" target="_blank"><u><font size="2" color="#0000FF">whitneyt@ca.ibm.com</font></u></a><font size="2" color="#5F5F5F"><br>Date: </font><font size="2">2021/03/10 07:52 AM</font><font size="2" color="#5F5F5F"><br>Subject: </font><font size="2">[EXTERNAL] Re: [llvm-dev] [GSoC 2021] Utilize LoopNest Pass</font><br><hr width="100%" size="2" align="left" noshade><br><font size="2" color="#FFFFFF"><br>ZjQcmQRYFpfptBannerEnd</font><br>I'm glad to get in touch with you two.<br>I'm planning to utilize LoopNest pass for some passes like loop unrolling.<br>Could you tell me more about this project if any?<br><br>2021年3月9日(火) 20:47 Whitney Tsang <<a href="mailto:whitney.uwaterloo@gmail.com" target="_blank"><u><font color="#0000FF">whitney.uwaterloo@gmail.com</font></u></a>>:
<ul><ul>+ Whitney, Ettore<br><br>On Tue, Mar 9, 2021, 3:00 AM uint256_t via llvm-dev <<a href="mailto:llvm-dev@lists.llvm.org" target="_blank"><u><font color="#0000FF">llvm-dev@lists.llvm.org</font></u></a>> wrote:<br>Hello,<br><br>I'm thinking of participating in GSoC at LLVM.<br>I've already talked about ideas with some project mentors but a newly added project idea "Utilize LoopNest Pass" attracted me. <br>I want to get in touch with its mentors (Whitney Tsang, Ettore Tiotto), whose email I couldn't find out.<br><br>Sincerely,<br>Toshiki Maekawa<br>_______________________________________________<br>LLVM Developers mailing list<u><font color="#0000FF"><br></font></u><a href="mailto:llvm-dev@lists.llvm.org" target="_blank"><u><font color="#0000FF">llvm-dev@lists.llvm.org</font></u></a><u><font color="#0000FF"><br></font></u><a href="https://urldefense.proofpoint.com/v2/url?u=https-3A__lists.llvm.org_cgi-2Dbin_mailman_listinfo_llvm-2Ddev&d=DwMFaQ&c=jf_iaSHvJObTbx-siA1ZOg&r=p0DGcdtx8-l1bvwJTLSk1zBTXpb78Y1slqHKTsTpRTE&m=xZta8ysMk2YLuaeN6hu48YbOcAibTj8EHetJ7EUKsC8&s=HbDn2cNobhWts-Cp8E5W7XgWSCD6ebFSWkwl_zDmusk&e=" target="_blank"><u><font color="#0000FF">https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev</font></u></a><br></ul></ul><br><br></ul><BR>
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