[llvm-dev] Question about using LoopAccessLegacyAnalysis

Michael Meng via llvm-dev llvm-dev at lists.llvm.org
Fri Feb 9 12:04:47 PST 2018

Hi Wei-Ren,

Thanks for your reply.

I use --debug-pass=Structure and it says Loop access analysis pass is executed before my pass. The interesting part is when I use -mem2reg and -loop-rotate it returns dependence information. I have no idea how to explain that. I would be great if one could help me with it. Thanks in advance.



From: llvm-dev <llvm-dev-bounces at lists.llvm.org> on behalf of 陳韋任 via llvm-dev <llvm-dev at lists.llvm.org>
Sent: Thursday, February 8, 2018 7:06:30 AM
To: Kewen Meng
Cc: LLVM Developers Mailing List
Subject: Re: [llvm-dev] Question about using LoopAccessLegacyAnalysis

Have you check `LoopAccessLegacyAnalysis::runOnFunction` ran as you expect? Besides, I am not sure if `LoopAccessLegacyAnalysis::runOnFunction` does anything useful, have you check that, too?

2018-02-08 1:49 GMT+08:00 Kewen Meng via llvm-dev <llvm-dev at lists.llvm.org<mailto:llvm-dev at lists.llvm.org>>:
Hi LLVM community,

I am writing a custom pass for analyzing the dependence information for the memory access within a loop. I found “LoopAccessLegacyAnalysis” class useful, however I m not able to obtain information from that pass. Here is what I did to get the information:

// require pass
virtual void getAnalysisUsage(AnalysisUsage &AU) const

// processing
virtual bool runOnFunction(Function &F) {
         LoopInfo &li = getAnalysis<LoopInfoWrapperPass>().getLoopInfo();
         LoopAccessLegacyAnalysis &lala = getAnalysis<LoopAccessLegacyAnalysis>();

         for(LoopInfo::iterator lp = li.begin(); lp != li.end(); lp++)
             Loop *loop = *lp;
             const LoopAccessInfo &lai = lala.getInfo(loop);

              // need help here
              // I can’t get any information from the LoopAccessInfo instance.
              errs()<<lai.getNumLoads(); // return 0

// register
static RegisterPass<SkeletonPass> X("test", "test for using the existing pass",

I must be missing something important. Any response would be greatly appreciated!


Best regards,
LLVM Developers mailing list
llvm-dev at lists.llvm.org<mailto:llvm-dev at lists.llvm.org>

Wei-Ren Chen (陳韋任)
Homepage: https://people.cs.nctu.edu.tw/~chenwj
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