Re: [PATCH] Small type_hash_canon improvement

[Jakub Jelinek <jakub at redhat dot com>]

On Thu, May 04, 2017 at 06:21:17PM +0200, Richard Biener wrote:
> >the
> >only other user after all calls free_node in a loop, so it is highly
> >unlikely it would do anything there.
> >
> >If you mean the INTEGER_TYPE handling, then yes, I guess it could be
> >done in free_node too and can move it there.  If it was without
> >the && TREE_TYPE (TYPE_M*_VALUE (type)) == type extra checks, then it
> >is certainly unsafe and breaks bootstrap even, e.g. build_range_type
> >and other spots happily create INTEGER_TYPEs with min/max value that
> >have some other type.  But when the type of the INTEGER_CSTs is the
> >type we are ggc_freeing, anything that would refer to those constants
> >afterwards would be necessarily broken (as their TREE_TYPE would be
> >ggc_freed, possibly reused for something completely unrelated).
> >Thus I think it should be safe even in the LTO case and thus doable
> >in free_node.
> 
> OK.  OTOH LTO frees the whole SCC and thus doesn't expect any pointed to stuff
> to be freed.  Not sure if we allow double ggc_free of stuff.

We don't, that crashes miserably.

	Jakub