llvm dev - Dec 2014 - [LLVMdev] Keeping a std::vector<Loop*> in a ModulePass

To whom it may concern,

I'm writing a LLVM ModulePass as a part of my undergraduate dissertation
and I need to keep a list of pointers to all Loops within a Module.
I've tried the following bit of code (inside a runOnModule() method in my
ModulePass, I also have getAnalysisUsage setup properly with LoopInfo added
as required)

  std::vector<Loop*> loops;

  for (Module::iterator F = M.begin(), FEND = M.end(); F != FEND; ++F){
    if (!(*F).isDeclaration()){
      LoopInfo& LI = getAnalysis<LoopInfo>(*F);
      for(LoopInfo::iterator l = LI.begin(), lend = LI.end(); l != lend;
++l){
        loops.push_back(*l);
      }
    }
  }

However, if I try to print out the loops with

  for(auto l: loops){
    errs() << *l << "\n";
  }

I get runtime errors. Now, I understand why this is happening - the
LoopInfo object is not living between iterations of the outermost loop and
thus all pointers are invalidated. I tried keep a pair std::pair<Function*,
int> of a function pointer and the corresponding position of the loop in
the list from LI.begin() to LI.end() but this causes runtime exceptions as
well. The code for that looks like this:

  std::vector<std::pair<Function*,int>> loops;
  for (Module::iterator F = M.begin(), FEND = M.end(); F != FEND; ++F){
    if (!(*F).isDeclaration()){
      LoopInfo& LI = getAnalysis<LoopInfo>(*F);
      int count = 0;
      for(LoopInfo::iterator l = LI.begin(), lend = LI.end(); l != lend;
++l){
        if ((*l)->getLoopDepth() == 0) errs() << **l
<<"\n";
        loops.push_back(std::make_pair(F,count));
        ++count;
      }
    }
  }
  for(auto l: loops){
    LoopInfo& LI = getAnalysis<LoopInfo>(*l.first);
    errs() << *(*(LI.begin()) + l.second) << "\n";
  }

However, no luck again. Is there any way to keep pointers to all loops in a
Module Pass?

Thanks,

Bilyan
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Hi Bilyan,

I believe there is no easy way to do this.

Please check this thread in which they discuss this exact problem:
http://lists.cs.uiuc.edu/pipermail/llvmdev/2012-March/048138.html

Regards,
Victor.

2014-12-13 12:20 GMT-02:00 Bilyan Borisov <bilyan.borisov at
gmail.com>:
>
> To whom it may concern,
>
> I'm writing a LLVM ModulePass as a part of my undergraduate
dissertation
> and I need to keep a list of pointers to all Loops within a Module.
> I've tried the following bit of code (inside a runOnModule() method in
my
> ModulePass, I also have getAnalysisUsage setup properly with LoopInfo added
> as required)
>
>   std::vector<Loop*> loops;
>
>   for (Module::iterator F = M.begin(), FEND = M.end(); F != FEND; ++F){
>     if (!(*F).isDeclaration()){
>       LoopInfo& LI = getAnalysis<LoopInfo>(*F);
>       for(LoopInfo::iterator l = LI.begin(), lend = LI.end(); l != lend;
> ++l){
>         loops.push_back(*l);
>       }
>     }
>   }
>
> However, if I try to print out the loops with
>
>   for(auto l: loops){
>     errs() << *l << "\n";
>   }
>
> I get runtime errors. Now, I understand why this is happening - the
> LoopInfo object is not living between iterations of the outermost loop and
> thus all pointers are invalidated. I tried keep a pair
std::pair<Function*,
> int> of a function pointer and the corresponding position of the loop in
> the list from LI.begin() to LI.end() but this causes runtime exceptions as
> well. The code for that looks like this:
>
>   std::vector<std::pair<Function*,int>> loops;
>   for (Module::iterator F = M.begin(), FEND = M.end(); F != FEND; ++F){
>     if (!(*F).isDeclaration()){
>       LoopInfo& LI = getAnalysis<LoopInfo>(*F);
>       int count = 0;
>       for(LoopInfo::iterator l = LI.begin(), lend = LI.end(); l != lend;
> ++l){
>         if ((*l)->getLoopDepth() == 0) errs() << **l
<<"\n";
>         loops.push_back(std::make_pair(F,count));
>         ++count;
>       }
>     }
>   }
>   for(auto l: loops){
>     LoopInfo& LI = getAnalysis<LoopInfo>(*l.first);
>     errs() << *(*(LI.begin()) + l.second) << "\n";
>   }
>
> However, no luck again. Is there any way to keep pointers to all loops in
> a Module Pass?
>
> Thanks,
>
> Bilyan
>
> _______________________________________________
> LLVM Developers mailing list
> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>
>
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