Re: basic-block and profile-based optimizing (was Re: New attribute"infrequent"?)

[Andreas Jaeger <aj at suse dot de>]

John Levon <moz@compsoc.man.ac.uk> writes:

> On Fri, Aug 31, 2001 at 02:11:01PM +0200, Andreas Jaeger wrote:
>
>> Profile driven optimizations won't help directly in the case of
>> libraries where you can't profile.
>
> when can this happen ? What libraries can't be profiled ?

You cannot profile accuratly the C library.  It can be profiled - but
I don't expect that it's realistic:

- What kind of application will you use?  This needs to be a
  self-written application that calls all calls with typical
  arguments.
- How will you handle exceptional stuff?  Should those be called by
  the special application?  For example should strerror be called - or
  not?
- There're plenty of different types of applications and it's
  difficult to model even some of them.

For some small libraries you might get good results but not for
something complex like the GNU C library,

Andreas
-- 
 Andreas Jaeger
  SuSE Labs aj@suse.de
   private aj@arthur.inka.de
    http://www.suse.de/~aj