Re: [PATCH] Avoid some unnecessary set_cfun calls

[Richard Biener <rguenther at suse dot de>]

On Wed, 13 Nov 2013, Jakub Jelinek wrote:

> On Wed, Nov 13, 2013 at 11:27:10AM +0100, Richard Biener wrote:
> > > Also, I wonder if we couldn't defer the expensive ira_init, if the info
> > > computed by it is used only during RTL optimization passes (haven't verified
> > > it yet), then supposedly we could just remember using some target hook
> > > what the last state was when we did ira_init last time, and call ira_init
> > > again at the start of expansion or so if it is different from the last time.
> > > For i?86/x86_64/ppc* this would be whether the current function's
> > > DECL_FUNCTION_SPECIFIC_TARGET is the same as one for which ira_init has been
> > > called, for rx whether interrupt attribute is the same and for mips whatever
> > > is needed.
> > 
> > I wonder why we cannot move all the stuff we re-init to a member
> > of struct function (or rather have a pointer to that info there
> > to cache it across functions with the same options).  That is,
> > get rid of more global state?  That would make switching back
> > and forth cheaper.
> 
> Isn't that what the SWITCHABLE_TARGET stuff is all about?

Maybe - I didn't follow all the changes in this area.

> So, perhaps we should just define SWITCHABLE_TARGET on i?86/x86_64/powerpc*
> (and rx if maintainer cares) and tweak it to attach somehow
> struct target_globals * to TARGET_OPTION_NODE somehow.
> A problem might be that lots of the save_target_globals
> allocated structures are heap allocated rather than GC, so we might leak
> memory.  Wonder if save_target_globals couldn't just compute the
> aggregate size of all the structures it allocates with XCNEW right now
> (plus required alignment if needed) and just allocate them together
> with the ggc_alloc_target_globals after the target_globals structure
> itself.

If you want to re-use it from functions with same options don't you
have a hashtable anyway?  You could add a reference count.

Richard.