<div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr">I think this has to do with how the pass manager is populated when we give -O3 vs when we give particular pass names.<div>Some passes have multiple createXYZPass() methods that accept arguments too. These methods call non-default pass constructors, which in turn cause the passes to behave in a different manner.</div><div>eg:</div><div><div>Pass *llvm::createLICMPass() { return new LegacyLICMPass(); }</div><div>Pass *llvm::createLICMPass(unsigned LicmMssaOptCap,</div><div> unsigned LicmMssaNoAccForPromotionCap) {</div><div> return new LegacyLICMPass(LicmMssaOptCap, LicmMssaNoAccForPromotionCap);</div><div>}</div></div><div>or</div><div><div>Pass *createLoopVectorizePass() { return new LoopVectorize(); }</div><div>Pass *createLoopVectorizePass(bool InterleaveOnlyWhenForced,</div><div> bool VectorizeOnlyWhenForced) {</div><div> return new LoopVectorize(InterleaveOnlyWhenForced, VectorizeOnlyWhenForced);</div><div>}</div></div><div>When we give pass names, opt calls the default constructor (eg: LoopVectorize()) whereas when we give O3, it can call a different version.</div><div>You can check in PassManagerBuilder.cpp (populateModulePassManager, populateFunctionPassManager) to see where different versions are being populated. Those must be the points in the pipeline where the IR starts differing. </div></div></div></div></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Sat, May 11, 2019 at 10:09 PM Mehdi AMINI via llvm-dev <<a href="mailto:llvm-dev@lists.llvm.org" target="_blank">llvm-dev@lists.llvm.org</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div dir="ltr">Hi,</div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Thu, May 9, 2019 at 5:20 PM Rahim Mammadli via llvm-dev <<a href="mailto:llvm-dev@lists.llvm.org" target="_blank">llvm-dev@lists.llvm.org</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr">Dear developers,<div><br></div><div>I am trying to reproduce the results of applying opt -O3 to a source file in the form of LLVM IR. I want to get the same IR by manually ordering the passes used by O3 and passing them to opt. </div><div><br></div><div>To illustrate what I am doing on an example, as an input I use linpack benchmark from the LLVM test suite[1]:</div><div><br></div><div>1. First I produce the intermediate representation using clang:</div><div>clang -O3 -Xclang -disable-llvm-optzns -emit-llvm -S linpack-pc.c -o linpack-pc.ll<br></div><div><br></div><div>2. Then I use opt to optimize the IR:</div><div>opt -S -O3 -o linpack-pc-3.ll linpack-pc.ll<br></div><div><br></div><div>Now my goal is to produce the IR identical to linpack-pc-3.ll by passing a sequence of optimizations to opt. To get the list of optimizations used by opt for O3, I run this:</div><div>opt -O3 -disable-output -debug-pass=Arguments linpack-pc.ll<br></div><div><br></div><div>Which produces (shortened to avoid wasting space):</div><div><div>Pass Arguments: -tti -targetlibinfo -tbaa ...</div><div>Pass Arguments: -targetlibinfo -tti -tbaa ...</div><div>Pass Arguments: -domtree</div><div><br></div></div><div>So apparently there are three sequences of passes applied to IR as part of O3. I wasn't able to reproduce the same IR as linpack-pc-3.ll using these passes, I tried applying passes sequentially or concatenating them and passing as a single sequence to opt. Neither produced the needed output. Moreover the performance of the final executable downgraded by about 35%. I'm using LLVM 3.8 and my OS is Ubuntu 16.04.</div><div><br></div><div>[1] <a href="https://github.com/llvm/llvm-test-suite/blob/master/SingleSource/Benchmarks/Linpack/linpack-pc.c" target="_blank">https://github.com/llvm/llvm-test-suite/blob/master/SingleSource/Benchmarks/Linpack/linpack-pc.c</a></div><div> <br></div></div></div></div></div></div></blockquote><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div></div><div>I'd very much appreciate if you could help me with this. Thank you.</div></div></div></div></div></div></blockquote><div><br></div><div>Your approach seems sensible to me. I usually have been debugging this kind of problem by piping the output of the two runs with `-print-after-all` to files and diff them to find out where the difference pops in.</div><div><br></div><div>-- </div><div>Mehdi</div><div><br></div></div></div>
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</blockquote></div><br clear="all"><div><br></div>-- <br><div dir="ltr" class="gmail-m_3753848777816909818gmail_signature"><div dir="ltr"><div><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div dir="ltr"><div><font size="1"><span style="color:rgb(84,141,212);font-family:arial,helvetica,sans-serif">Regards</span><br></font></div><div><div dir="ltr"><font color="#000000" face="arial, helvetica, sans-serif" size="1"><font color="#548dd4">Bhatu</font></font></div></div></div></div></div></div></div></div></div></div>