Re: [commited] Reduce memory overhead of PRE bitmaps

[Michael Matz <matz at suse dot de>]

Hi,

On Tue, 7 Sep 2004, Devang Patel wrote:

> > Hi,
> > the attached patch move bitmaps used by PRE to obstacks to conserve
> > roughly 10% of GGC allocated memory.  I've bootstrapped and regtested it
> > on i686-pc-gnu-linux and will commit it shortly.  It has been approved
> > by Daniel on IRC.
> 
> I thought GCC is moving away from obstacks ?

For stuff with complicated lifetime.  But for things which come in big 
number and are small itself, and have a very constrained lifetime 
(especially the end of life has to be a defined point, like for instance 
the end of a certain optimization pass), obstacks (or allocpool) are just 
perfect.

> Side note: All these memory managers makes me dizzy sometimes :). It'd
> be helpful if there is one document describing which one to use in which
> situations.

complicated lifetime -> ggc
defined end-of-life, many small  -> obstacks/allocpool
defined end-of-life, few big -> malloc/free

It's complicated by the fact, that ggc stuff can't easily stay just inside 
non-ggc stuff (you have to register some roots).


Ciao,
Michael.