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Re: WHOPR bootstrap, when/how?


> Well, I think this is independent.
> It makes a lot of sense to make profiling to work in a way so instrumentation
> happens at linktime with LTO and we can read stuff back.  This is relatively
> easy to do: we need to rewrite profiling pass to work on SSA (that is easy and
> desirable anyway and on my TODO for a while).  Then we need to split gcov and
> -fprofile-generate profiling passes.  Gcov needs to happen early since early
> optimization will optimize out dead code and we want to count it.
> Profile generation needs to be done late since we want it at linktime.
> 
> Then we will be able to do profiling at LTO.
> 
> With WHOPR I expect situation to be bit funnier, since one does not have
> the function bodies and thus it is difficult to read in the profile,
> get callgraph profile and do something about it.

And as for profiling, I would hope WHOPR to be solution for building large application
with whole program optimization.  LIPO or any sort of profile driven partitioning is not
that.  Just very few users will bother with profiling, while LTO/WHOPR has chance to be
transparent enough to be widely adopted.
So I think tying WHOPR and profile feedback too close together is a mistake.

Honza


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