[Bug rtl-optimization/56921] [4.9 Regression] ICE in rtx_cost called by doloop_optimize_loops for PPC

["rguenther at suse dot de" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56921

--- Comment #9 from rguenther at suse dot de <rguenther at suse dot de> 2013-04-12 08:45:46 UTC ---
On Fri, 12 Apr 2013, steven at gcc dot gnu.org wrote:

> 
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56921
> 
> --- Comment #8 from Steven Bosscher <steven at gcc dot gnu.org> 2013-04-12 08:36:04 UTC ---
> (In reply to comment #7)
> > niter_desc is not marked GTY(()) but is cached from struct loop aux field.
> > niter_desc uses heap memory but points to GC memory.  Thus, caching of this
> > across passes is not safe.
> > I suppose passes are missing free_simple_loop_desc, loop-doloop.c calls
> > get_simple_loop_desc but never free_simple_loop_desc for example (which
> > then at least leaks the niter_desc memory).
> 
> Another, IMHO better, solution would be to not use loop->aux but make
> a GC-safe vec indexed by loop->num. Maybe add checking in the loop
> verifier that no struct niter_desc is left pending if its parent loop
> is removed.
> 
> That should make the loop passes GC safe.
> 
> Then mark all "aux" fields as GC unsafe and document that every pass is
> responsible for cleaning up after itself.

Yes, definitely.  I was bit once by this ->aux usage which is
not really obvious.

Richard.