On Thu, 14 Mar 2019, Jakub Jelinek wrote:
> On Wed, Mar 13, 2019 at 10:08:09PM -0400, Jason Merrill wrote:
> > > The following testcase ICEs since my recent cxx_eval_loop_expr changes.
> > > The problem is that the Forget saved values of SAVE_EXPRs. inside of the
> > > loop can remove SAVE_EXPRs from new_ctx.values and if that is the last
> > > iteration, we can also do the loop at the end of function (which has been
> > > added there mainly to handle cases where the main loop breaks earlier)
> > > and new_ctx.values->remove ICEs because *iter is already not in the table.
> >
> > It shouldn't ICE, remove_elt_with_hash is documented to do nothing if the
> > element is not in the table.
> >
> > Does this untested patch fix the test?
>
> This changed in https://gcc.gnu.org/ml/gcc-patches/2000-02/msg00988.html
> Before that change, it has been documented that:
> "Naturally the hash table must already exist."
> That patch changed it to do
> slot = htab_find_slot (htab, element, 0);
> if (*slot == EMPTY_ENTRY)
> return;
> but htab_find_slot actually never returns *slot == EMPTY_ENTRY if called
> with insert 0:
> + if (!insert)
> + return NULL;
> It can return *slot == EMPTY_ENTRY only if insert is non-zero, and
> otherwise it must be (for both cases) a non-deleted non-empty entry equal to
> the one we are looking for.
>
> Thus, I believe what is documented since that patch has never worked and we
> are wasting cycles (if not optimized out) testing something impossible.
>
> So, I think our options are either to make it work, like below (untested),
> or remove those ifs altogether and put back the
> "Naturally the hash table must already exist." comment.
I'd say make it work, thus your patch below is OK.
Richard.
> 2019-03-14 Jason Merrill <ja...@redhat.com>
> Jakub Jelinek <ja...@redhat.com>
>
> * hash-table.h (remove_elt_with_hash): Return if slot is NULL rather
> than if is_empty (*slot).
>
> * hashtab.c (htab_remove_elt_with_hash): Return if slot is NULL rather
> than if *slot is HTAB_EMPTY_ENTRY.
>
> --- gcc/hash-table.h.jj 2019-01-01 12:37:17.446970209 +0100
> +++ gcc/hash-table.h 2019-03-14 08:48:18.861131498 +0100
> @@ -940,7 +940,7 @@ hash_table<Descriptor, Allocator>
> ::remove_elt_with_hash (const compare_type &comparable, hashval_t hash)
> {
> value_type *slot = find_slot_with_hash (comparable, hash, NO_INSERT);
> - if (is_empty (*slot))
> + if (slot == NULL)
> return;
>
> Descriptor::remove (*slot);
> --- libiberty/hashtab.c.jj 2019-01-01 12:38:46.868503025 +0100
> +++ libiberty/hashtab.c 2019-03-14 08:47:49.172612001 +0100
> @@ -725,7 +725,7 @@ htab_remove_elt_with_hash (htab_t htab,
> PTR *slot;
>
> slot = htab_find_slot_with_hash (htab, element, hash, NO_INSERT);
> - if (*slot == HTAB_EMPTY_ENTRY)
> + if (slot == NULL)
> return;
>
> if (htab->del_f)
>
>
> Jakub
>
--
Richard Biener <rguent...@suse.de>
SUSE LINUX GmbH, GF: Felix Imendoerffer, Jane Smithard, Graham Norton, HRB
21284 (AG Nuernberg)
