Re: [RFC] two-phase marking in gt_cleare_cache

[Richard Biener <richard dot guenther at gmail dot com>]

On Mon, Jul 6, 2015 at 10:57 AM, Tom de Vries <Tom_deVries@mentor.com> wrote:
> Hi,
>
> Using attached untested patch, I managed to minimize a test-case failure for
> PR 66714.
>
> The patch introduces two-phase marking in gt_cleare_cache:
> - first phase, it loops over all the hash table entries and removes
>   those which are dead
> - second phase, it runs over all the live hash table entries and marks
>   live items that are reachable from those live entries
>
> By doing so, we make the behaviour of gt_cleare_cache independent of the
> order in which the entries are visited, turning:
> - hard-to-trigger bugs which trigger for one visiting order but not for
>   another, into
> - more easily triggered bugs which trigger for any visiting order.
>
> Any comments?

I think it is only half-way correct in your proposed change.  You only
fix the issue for hashes of the same kind.  To truly fix the issue you'd
have to change generated code for gt_clear_caches () and provide
a clearing-only implementation (or pass a operation mode bool to
the core worker in hash-table.h).

Thanks,
Richard.

> Thanks,
> - Tom