[Bug middle-end/35544] Error with -fprofile-use

["xinliangli at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #4 from xinliangli at gmail dot com  2008-03-12 06:40 -------
(In reply to comment #3)
> (In reply to comment #2)
> > This model won't work well when -O4 (ipo) is in place. If instrumentation and
> > annotation happens at the same phase in the compiler pipeline, I don't see a
> > reason why such restriction is needed.
> 
> Why do you think it will not work well with LTO?

At least it is tricky with cross module inlining happening for instrumented
functions -- the inline instances should really updating counters in the
original routines.

Besides, this requirement will significantly slow down an instrumented compile
for IPO.


> 
> The instrumentation and annotation already happens at the same place which is
> why the same options are required. 

Sounds like 'same options' is sufficient for that to happen, but not necessary.

> They just happen after some inlining and
> other early optimization to make sure the profiling does not get too slow.

If the early optimizations always happen at -O1 and above, a more reasonable
requirement is that instrumentation compile must be done at -O1 and above.
Again, how much performance gain can be achieved with early optimization for
instrumented binary (which is slow anyway)?

David

> 
> -- Pinski
> 


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=35544