llvm dev - Dec 2020 - registering passes at the beginning/end of opt passes (new pass manager)

Hello all,

Can I register passes at the beginning/end of opt passes (new pass manager)?

I found that
registerPipelineStartEPCallback/registerOptimizerLastEPCallback work
successfully for clang, but they don't fire when opt -passes="" is
used.

Thanks,
Juneyoung
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I’m not sure what’s your context. I think  `-passes` is only used for specify
the entire pipeline instead of inserting callbacks into an existing pipeline.

You can either directly modify PassBuilder’s code to run Passes before/after a
Pass.
Or writing a new PassManager PassPlugin and use the PassBuilder instance in
there (see the comments in include/llvm/Passes/PassPlugin.h [1]) to call
registerPipelineStartEPCallback. Then load that plugin using opt.

[1]
https://github.com/llvm/llvm-project/blob/master/llvm/include/llvm/Passes/PassPlugin.h#L96
<https://github.com/llvm/llvm-project/blob/master/llvm/include/llvm/Passes/PassPlugin.h#L96>

Best
-Min
> On Dec 3, 2020, at 8:28 PM, Juneyoung Lee via llvm-dev <llvm-dev at
lists.llvm.org> wrote:
> 
> Hello all,
> 
> Can I register passes at the beginning/end of opt passes (new pass
manager)?
> 
> I found that
registerPipelineStartEPCallback/registerOptimizerLastEPCallback work
successfully for clang, but they don't fire when opt -passes="" is
used.
> 
> Thanks,
> Juneyoung
> 
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
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There are various opt options [1] that let you specify passes to add at
specific points in the pipeline. Also, specifying a target may cause the
corresponding TargetMachine to register pass callbacks.
Something like "-passes=default<O2>" that creates a full
pipeline will add
those passes to the pipeline. Otherwise they aren't invoked.

[1]:
https://github.com/llvm/llvm-project/blob/f5f1a5c2448e31f3c7e6f85b378372a02f8d3e43/llvm/tools/opt/NewPMDriver.cpp#L73

On Thu, Dec 3, 2020 at 8:29 PM Juneyoung Lee via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> Hello all,
>
> Can I register passes at the beginning/end of opt passes (new pass
> manager)?
>
> I found that
> registerPipelineStartEPCallback/registerOptimizerLastEPCallback work
> successfully for clang, but they don't fire when opt
-passes="" is used.
>
> Thanks,
> Juneyoung
>
> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
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Okay, I tried something like this:

Given opt -passes='...', my bash script strips the quotes, puts
module(mypass) at the begin/end, put quotes again, and runs it. mypass is a
module-level pass.

ex) Given opt -passes='sroa' , it emits opt
-passes='module(mypass),sroa,module(mypass)'

The emitted command seems working in this case, but I found that it breaks
when loop-level passes are there:

ex) Running opt
-passes='module(mypass),loop(unswitch<nontrivial>),module(mypass)'
shows:
build/bin/opt: invalid use of 'loop' pass as module pipeline


Is there a way to correctly add 'mypass' to the begin/end of the passes
regardless of the level of the pipeline?

Thanks,
Juneyoung

On Fri, Dec 4, 2020 at 1:28 PM Juneyoung Lee <juneyoung.lee at
sf.snu.ac.kr>
wrote:
> Hello all,
>
> Can I register passes at the beginning/end of opt passes (new pass
> manager)?
>
> I found that
> registerPipelineStartEPCallback/registerOptimizerLastEPCallback work
> successfully for clang, but they don't fire when opt
-passes="" is used.
>
> Thanks,
> Juneyoung
>
>
-- 

Juneyoung Lee
Software Foundation Lab, Seoul National University
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