llvm dev - Jun 2018 - ModulePass cannot be registered as EarlyAsPossible

Hello all,

I've followed the example in
https://github.com/CompilerTeaching/SimplePass/blob/master/SimplePass.cc in
order to create a custom pass.

The pass needs to be added before any transformation, so I used
EP_EarlyAsPossible extension point to register it.  Furthermore, I need to
access to every GlobalVariable in the IR, so my pass has to be a
ModulePass, like this:

  struct MyPass : public ModulePass {
     static char ID;
     MyPass(): ModulePass(ID) {}
     virtual bool runOnModule(Module &M) {...}
  ...
  }

However, every time I try to access to the Module object M inside
runOnModule(), clang just crashes.  Even a debug message like *outs() <<
M.getName() << '\n';* would cause a segfault. So am I doing
something
wrong, like EP_EarlyAsPossible is really not to be used with ModulePasses,
or is this rather a bug?

In case this is not a bug, what would be the best way to manipulate an IR
Module as it is coming right out of the frontend?

Thanks for your help,

Son Tuan Vu
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Hi,

EP_EarlyAsPossible only works with FunctionPasses, yes. If you look at 
how it's used in PassManagerBuilder, it is only invoked from 
populateFunctionPassManager.

The earliest you can add ModulePasses is with EP_ModuleOptimizerEarly. 
However, those passes are not added on O0. If the OptLevel is 0, you can 
instead add the passes to EP_EnabledOnOptLevel0.

This might not be early enough for you, but those are the points that 
are available for module passes as far as I know.

Regards,
Bevin


On 2018-06-12 15:46, Son Tuan VU via llvm-dev wrote:
> Hello all,
>
> I've followed the example in 
> https://github.com/CompilerTeaching/SimplePass/blob/master/SimplePass.cc 
> in order to create a custom pass.
>
> The pass needs to be added before any transformation, so I used 
> EP_EarlyAsPossible extension point to register it. Furthermore, I need 
> to access to every GlobalVariable in the IR, so my pass has to be a 
> ModulePass, like this:
>
>   struct MyPass : public ModulePass {
>      static char ID;
>      MyPass(): ModulePass(ID) {}
>      virtual bool runOnModule(Module &M) {...}
>   ...
>   }
>
> However, every time I try to access to the Module object M inside 
> runOnModule(), clang just crashes.  Even a debug message like *outs() 
> << M.getName() << '\n';* would cause a segfault. So am
I doing
> something wrong, like EP_EarlyAsPossible is really not to be used with 
> ModulePasses, or is this rather a bug?
>
> In case this is not a bug, what would be the best way to manipulate an 
> IR Module as it is coming right out of the frontend?
>
> Thanks for your help,
>
> Son Tuan Vu
>
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
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Hi Bevin,

Thank you for your reply. Unfortunately, I was using
EP_ModuleOptimizerEarly and I just realized that it is not early enough,
since the FunctionPassManager does apply some basic optimization on the
functions before any Module optimizations...

So there's no way to insert a Module pass earlier than
ModuleOptimizerEarly? I will try to hack it as Björn pointed out then.

Thanks for your help,


Son Tuan Vu

On Wed, Jun 13, 2018 at 4:01 PM, Bevin Hansson via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> Hi,
>
> EP_EarlyAsPossible only works with FunctionPasses, yes. If you look at how
> it's used in PassManagerBuilder, it is only invoked from
> populateFunctionPassManager.
>
> The earliest you can add ModulePasses is with EP_ModuleOptimizerEarly.
> However, those passes are not added on O0. If the OptLevel is 0, you can
> instead add the passes to EP_EnabledOnOptLevel0.
>
> This might not be early enough for you, but those are the points that are
> available for module passes as far as I know.
>
> Regards,
> Bevin
>
> On 2018-06-12 15:46, Son Tuan VU via llvm-dev wrote:
>
> Hello all,
>
> I've followed the example in https://github.com/
> CompilerTeaching/SimplePass/blob/master/SimplePass.cc in order to create
> a custom pass.
>
> The pass needs to be added before any transformation, so I used
> EP_EarlyAsPossible extension point to register it.  Furthermore, I need to
> access to every GlobalVariable in the IR, so my pass has to be a
> ModulePass, like this:
>
>   struct MyPass : public ModulePass {
>      static char ID;
>      MyPass(): ModulePass(ID) {}
>      virtual bool runOnModule(Module &M) {...}
>   ...
>   }
>
> However, every time I try to access to the Module object M inside
> runOnModule(), clang just crashes.  Even a debug message like *outs()
<<
> M.getName() << '\n';* would cause a segfault. So am I doing
something
> wrong, like EP_EarlyAsPossible is really not to be used with ModulePasses,
> or is this rather a bug?
>
> In case this is not a bug, what would be the best way to manipulate an IR
> Module as it is coming right out of the frontend?
>
> Thanks for your help,
>
> Son Tuan Vu
>
>
> _______________________________________________
> LLVM Developers mailing listllvm-dev at
lists.llvm.orghttp://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
>
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
>
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