Re: [PATCH] Disable -fno-reorder-blocks-and-partition if no -fprofile-use to avoid unnecessary overhead

[Jan Hubicka <hubicka@ucw.cz>]

> > What has changed between then and now? Also, do we not use
> > estimates/heuristics when not using a profile?
> 
> Nothing has changed - splitting effectively never kicked in without a
> profile. Honza and I had discussed the idea that static profile
> heuristics could eventually be used to distinguish hot vs cold bbs,

Yep, the basic idea was to move EH clenaups to the cold section for start.  The
cleanup code can get surprisingly large for some C++ apps.

> but that hasn't happened. What I didn't notice until recently was the
> size increase in the .o files from varasm adding in unnecessary
> sections and labels when this option was on. Unless and until static

Perhaps we also may just teach varasm to not output those when function is not
split.  I am happy with the patch as it is because it is pointless to run the
code when no splitting happens.

Honza
> heuristics are used to distinguish cold bbs in
> probably_never_executed_bb_p, I don't think it makes sense to do
> anything finer grained that just disabling the option.
> 
> Teresa
> 
> >
> >
> > Bernd
> 
> 
> 
> -- 
> Teresa Johnson | Software Engineer | tejohnson@google.com | 408-460-2413