<html><head><meta http-equiv="Content-Type" content="text/html; charset=us-ascii"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;" class="">Hi Armand,<div class=""><br class=""></div><div class="">You can print the frequency of the blocks at the machine level.</div><div class="">If that frequency comes from pgo, these numbers should be accurate.</div><div class=""><br class=""></div><div class="">Take a look at <span style="font-family: Menlo; font-size: 11px;" class="">-view-machine-block-freq-propagation-dags=fraction </span>for instance.</div><div class=""><br class=""></div><div class="">Then, you should be able to just use the assembly file annotation like you were doing.</div><div class=""><br class=""></div><div class="">Cheers,</div><div class="">-Quentin</div><div class=""><br class=""><div><blockquote type="cite" class=""><div class="">On Nov 30, 2020, at 3:30 PM, Armand Behroozi via llvm-dev <<a href="mailto:llvm-dev@lists.llvm.org" class="">llvm-dev@lists.llvm.org</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div dir="ltr" class="">Hello,<div class=""><br class=""></div><div class="">How would people recommend using LLVM (if at all) to get the dynamic spill/reload count and total number of instructions for a program? Speed and efficiency are unimportant. I just want it to be correct.</div><div class=""><br class=""></div><div class="">I'm using a debug build of LLVM 12 "clang version 12.0.0" on an x86_64-unknown-linux-gnu cpu.<br class=""></div><div class=""><br class=""></div><div class=""><br class=""></div><div class=""><div class=""><b class=""><u class="">What I've tried:</u></b></div></div><div class=""><div class="">I thought I'd use llvm's pgo to get asm BB counts and then multiply by the number of static spills and reloads in each asm BB. <br class=""></div><div class=""><br class=""></div><div class="">LLC annotates lines in the assembly file that result in spills and reloads i.e.:</div><div class="">movq %rax, -24(%rsp) # 8-byte Spill<br class=""> movq -16(%rsp), %rax # 8-byte Reload<br class=""></div><div class=""><br class=""></div><div class="">I couldn't find a way to instrument asm BBs w/ pgo using LLC, so I'm doing it at the IR level like this:</div><div class="">clang -emit-llvm -gline-tables-only -O3 file1.c file1.bc</div><div class="">opt -pgo-instr-gen -instrprof file1.bc -o file1.prof.bc </div><div class="">clang -fprofile-instr-generate file1.prof.bc file2.prof.bc etc.</div><div class="">-run it-</div><div class="">llvm-profdata merge -output=pgo.profdata default.profraw</div><div class="">opt -pgo-instr-use -pgo-test-profile-file=pgo.profdata -load mypass file.bc</div><div class=""><br class=""></div><div class="">Where "mypass" iterates through all the IR BBs and prints out the label and block frequency info.</div><div class=""><br class=""></div><div class="">I've quickly realized that asm BBs don't directly correspond to IR BBs b/c the CFG changes during code generation. Although I've managed to make a mostly correct mapping between IR BBs and asm BBs using their debug labels, it's been kind of messy. For example:</div><div class="">There is the odd situation where I'll find 2 asm BBs with the same debug label w/ pgo counters to different memory addresses.</div></div><div class=""><br class=""></div><div class="">There are also other complications where the pgo CFG is different from the original CFG, so I'm not convinced this is the correct way to go about it.</div><div class=""><br class=""></div><div class=""><br class=""></div><div class=""><b class=""><u class="">What I thought I'd try next</u></b></div><div class="">I wanted to write a MachineFunctionPass that gets a BB's static spill/reload count and then inserts a function call to keep track of its execution frequency. The pass would be run after all CFG changes have been made. There's a comment in X86TargetMachine.cpp that says: </div><div class="">" </div><div class="">// The X86 Speculative Execution Pass must run after all control</div>// flow graph modifying passes.<div class="">"</div><div class="">This is in void X86PassConfig::addPreEmitPass2(), and I was going to add my pass here. Since the function call would clobber registers, I was going to either re-run register allocation or callee save all the registers the function would use.</div><div class=""><br class=""></div><div class="">Any help/feedback would be appreciated.</div><div class=""><br class=""></div><div class="">Thank you.</div><div class=""><br class=""></div><div class="">Regards,</div><div class=""><br class=""></div><div class="">Armand Behroozi</div></div>
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