Re: RFA: Don't use obsavestring in dwarf2read

[Daniel Jacobowitz <drow@mvista.com>]

On Thu, Feb 05, 2004 at 03:34:30PM -0500, Elena Zannoni wrote:
>  > The obstacks themselves are probably a good idea.  Once upon a time,
>  > Peter informed me, there was a plan to free the psymbol obstack when
>  > all symbols had been read in; but that doesn't seem like a useful
>  > optimization, and I can't think offhand of any use for separate symbol
>  > and type obstacks.  I wouldn't object to having a per-objfile obstack
>  > instead, and un-seperating them.
> 
> I think it would be worthwhile to see how much doing that would save us.

Well, it wouldn't save anything by itself - there's immeasurable
overhead to the obstacks.  It would let us eliminate this sort of
duplication, but they're pretty tricky to identify; it took me a couple
of hours to convince myself about this set of 'em.

>  > > [BTW why are only few obstack properly initialized?]
>  > 
>  > Which do you mean?
>  > 
> 
> I grepped for obstack_init, and only a few obstacks call that
> function. Form the obstack doco, it seems that it needs to be
> called. I wonder if the function was introduced later on in libiberty,
> as an afterthought.

It looks like obstack_specify_allocation and obstack_init fill the same
role.  The objfile's obstacks use the former.

> Ah, ok, it's because of the nature of the program you were handling. I
> was trying to imagine how the overhead of obstack themselves could be
> that large. It seems to me that this is a good argument for an 'on
> demand' symbol reading implementaion.  But, yes the various dwarf2
> sections are already in the psymbol_obstack. And we are duplicating
> that again on the type_obstack. :-( 

Right.  I'm not sure how much of this can be done on demand that isn't
already; if I wasn't clear about this, the 100MB was a worst-case
number (-readnow).  Without -readnow it's much less.

>  > Another large portion comes from not duplicating the names of types in
>  > the typedef symbols associated with the type.  One was on type_obstack,
>  > the other on symbol_obstack.
>  > 
> 
> Right; this would also go away if we unify the obstacks.

-- 
Daniel Jacobowitz
MontaVista Software                         Debian GNU/Linux Developer