Re: Profiling on S390

[Jan Hubicka <jh@suse.cz>]

> On Tue, Apr 22, 2003 at 10:43:37PM +0200, Ulrich Weigand wrote:
> > >It looks very unsafe for me - GCC assumes at many places that CC is not
> > >live accross boundaries.
> > 
> > This is annoying.  Is there any fundamental reason for this restriction?
> 
> No, and it's not actually true.
> 
> What is true is that you can't generally move the thing around
> if most of your instructions clobber the flags.  So e.g. for x86
> this would be a Really Bad Idea, but for Sparc it can work out.

My impression is that s390 is x86-like when dealing with flags.
> 
> It's also true that some of the simplifiers (cse, combine) won't
> DTRT unless the compare and use are in the same block.
> 
> > Can't the profiler use special code to save/restore CC?
> 
> It could, but if you don't have add/load/store insns that don't
> clobber CC, then you'll get in trouble with reload too.  Of
We can conclude to use some named patterns.  For instance
"save_state" "restore_state" to fold profiler code in.  Does this sound
plausible?

Honza
> course, that brings up the issue of getting the right pattern
> emitted from the profiler.  Could be done with a special named
> add pattern, but that seems like a lot of overhead for very
> little return.
> 
> This is all about a movstrsi or cmpstrsi pattern?  Perhaps it
> would be better to keep this as one unit until after reload?
> 
> 
> r~