Re: [PATCH][RFC] Less TODO_remove_unused_locals

[Jan Hubicka <jh at suse dot cz>]

> > Hunting for the "we're getting slower" bits I noticed that
> > TODO_remove_unused_locals is a big part of execute_function_todo
> > (and accounts for 1% of compile-time of ac.f90).
> > The following patch removes most of the remove_unused_locals
> > calls based on the fact that with anonymous SSA names now available
> > we should never create new locals (wishful thinking of course ...)

We still can kill references to existing ones.

> > and the important places to remove unused stuff are driven by
> > 1) avoid creating yet another copy of the unused stuff, thus do
> > it before inlining, on the callee;  2) avoid pinning unused memory
> > while we operate on other function bodies, thus, do it at the end
> > of non-IPA pass pipelines
> >
> > In the end this asks for more explicit placement and thus a
> > real pass ... but the following should be enough as a RFC and
> > be good enough for 4.8.

Yes, it looks good to me.  I introduced this remove_unused_locals stuff
and I was aware it is executed quite too often. I meant to get some  
data on this
but never got around that and moreover the number of execution has increased
over the years as we increased number of passes...

My recollection is that at that time the pass also did dropping of  
some flags (ADDRESSABLE?) promoting into Gimple registers.  This was  
motivation to keep it working often since it was code quality thing  
too. I suppose this is now done elsewhere.

Honza