[llvm-dev] OptBisect implementation for new pass manager
Fedor Sergeev via llvm-dev
llvm-dev at lists.llvm.org
Wed Sep 26 09:53:52 PDT 2018
As the generic Pass Instrumentation framework for new pass manager is
I'm glad to start the discussion on implementation of -opt-bisect
through that framework.
As it has already been discovered while porting other features (namely,
blindly copying the currently existing legacy implementation is most
likely not a perfect
way forward. Now is a chance to take a fresh look at the overall
approach and perhaps
do better, without the restrictions that legacy pass manager framework
Kind of a summary of what we have now:
- There is a single OptBisect object, requested through LLVMContext
(managed as ManagedStatic).
- OptBisect is defined in lib/IR, but does use analyses,
which is a known layering issue
- Pass hierarchy provides skipModule etc helper functions
- Individual passes opt-in to OptBisect activities by manually
calling skip* helper functions
With current state of new-pm PassInstrumentation potential OptBisect
will have the following properties/issues:
- OptBisect object that exists per compilation pipeline, managed
similar to PassBuilder/PassManagers
(which makes it more suitable for use in parallel compilations)
- no more layering issues imposed by implementation since
instrumentations by design
can live anywhere - lib/Analysis, lib/Passes etc
- since Codegen is still legacy-only we will have to make a joint
provides a sequential passes numbering through both new-PM IR and
legacy Codegen pipelines
- as of right now there is no mechanism for opt-in/opt-out, so it
needs to be designed/implemented
Here I would like to ask:
- what would be preferable - opt-in or opt-out?
- with legacy implementation passes opt-in both for bisect and
attribute-optnone support at once.
Do we need to follow that in new-pm implementation?
Also, I would like to ask whether people see current user interface for
Do we need better controls for more sophisticated bisection?
Basically I'm looking for any ideas on improving opt-bisect user
experience that might
affect design approaches we take on the initial implementation.
More information about the llvm-dev