[llvm-dev] OptBisect implementation for new pass manager

Fedor Sergeev via llvm-dev
Wed, 26 Sep 2018 18:55:28 -0000

On 09/26/2018 08:13 PM, David Greene wrote:
 > Fedor Sergeev <fedor.sergeev at azul.com> writes:
 >
 >>         - 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 opt-bisect limiting?
 >
 > Ideally I would prefer an opt-out model.  Practiclaly speaking, I'm
not
 > sure that's possible.  Presumably opt-bisect doesn't apply to
analysis
 > passes.
Sure it doesnt.

 >   What happens if a transformation pass depends on another
 > transformation pass earlier in the pipeline?  If the earlier
 > transformation pass is bisected out, then...???
If we talk about current bisection scheme then the only passes that
are run after the bisection point are those required-to-run passes.
And that means required passes should not depend on anything else than
other required passes. Which seems to be a very reasonable restriction
to me.

 > It seems to me that optnone and opt-bisect are two different things and
 > therefore they should be handled orthogonally.
I have heard this opinion more than once :)
Makes sense to me as well.

regards,
   Fedor.