Re: [PATCH] middle-end/114604 - ranger allocates bitmap without initialized obstack

[Richard Biener <rguenther@suse.de>]

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On Tue, 9 Apr 2024, Aldy Hernandez wrote:

> BTW, I'm not opposed to this patch.  Thank you for tracking this down,
> and feel free to commit as is if y'all PMs agree it's OK.  I just
> wanted to know if there's a better way going forward.  I can certainly
> put it on my TODO list once stage1 opens again.
> 
> And no, there probably isn't an obstack for those classes, but I
> wonder if we should have a class local one, as we do for the rest of
> the classes.

OK, I pushed it now, it looks like the GCC 13 branch isn't affected
in obviously the same way (but I didn't try instrumenting there).

Feel free to improve next stage1.

Richard.

> Aldy
> 
> On Mon, Apr 8, 2024 at 7:47 PM Richard Biener
> <richard.guenther@gmail.com> wrote:
> >
> >
> >
> > > Am 08.04.2024 um 18:40 schrieb Aldy Hernandez <aldyh@redhat.com>:
> > >
> > > On Mon, Apr 8, 2024 at 6:29 PM Richard Biener <rguenther@suse.de> wrote:
> > >>
> > >>
> > >>
> > >>>> Am 08.04.2024 um 18:09 schrieb Aldy Hernandez <aldyh@redhat.com>:
> > >>>
> > >>> On Mon, Apr 8, 2024 at 5:54 PM Jakub Jelinek <jakub@redhat.com> wrote:
> > >>>>
> > >>>> On Mon, Apr 08, 2024 at 05:40:23PM +0200, Aldy Hernandez wrote:
> > >>>>>>       PR middle-end/114604
> > >>>>>>       * gimple-range.cc (enable_ranger): Initialize the global
> > >>>>>>       bitmap obstack.
> > >>>>>>       (disable_ranger): Release it.
> > >>>>>> ---
> > >>>>>> gcc/gimple-range.cc | 4 ++++
> > >>>>>> 1 file changed, 4 insertions(+)
> > >>>>>>
> > >>>>>> diff --git a/gcc/gimple-range.cc b/gcc/gimple-range.cc
> > >>>>>> index c16b776c1e3..4d3b1ce8588 100644
> > >>>>>> --- a/gcc/gimple-range.cc
> > >>>>>> +++ b/gcc/gimple-range.cc
> > >>>>>> @@ -689,6 +689,8 @@ enable_ranger (struct function *fun, bool use_imm_uses)
> > >>>>>> {
> > >>>>>>  gimple_ranger *r;
> > >>>>>>
> > >>>>>> +  bitmap_obstack_initialize (NULL);
> > >>>>>> +
> > >>>>>>  gcc_checking_assert (!fun->x_range_query);
> > >>>>>>  r = new gimple_ranger (use_imm_uses);
> > >>>>>>  fun->x_range_query = r;
> > >>>>>> @@ -705,6 +707,8 @@ disable_ranger (struct function *fun)
> > >>>>>>  gcc_checking_assert (fun->x_range_query);
> > >>>>>>  delete fun->x_range_query;
> > >>>>>>  fun->x_range_query = NULL;
> > >>>>>> +
> > >>>>>> +  bitmap_obstack_release (NULL);
> > >>>>>
> > >>>>> Are you not allowed to initialize/use obstacks unless
> > >>>>> bitmap_obstack_initialize(NULL) is called?
> > >>>>
> > >>>> You can use it with some other obstack, just not the default one.
> > >>>>
> > >>>>> If so, wouldn't it be
> > >>>>> better to lazily initialize it downstream (bitmap_alloc, or whomever
> > >>>>> needs it initialized)?
> > >>>>
> > >>>> No, you still need to decide where is the safe point to release it.
> > >>>> Unlike the non-default bitmap_obstack_initialize/bitmap_obstack_release,
> > >>>> the default one can nest (has associated nesting counter).  So, the above
> > >>>> patch just says that ranger starts using the default obstack in
> > >>>> enable_ranger and stops using it in disable_ranger and anything ranger
> > >>>> associated in the obstack can be freed at that point.
> > >>>
> > >>> I thought ranger never used the default one:
> > >>>
> > >>> $ grep bitmap_obstack_initialize *value* *range*
> > >>> value-relation.cc:  bitmap_obstack_initialize (&m_bitmaps);
> > >>> value-relation.cc:  bitmap_obstack_initialize (&m_bitmaps);
> > >>> gimple-range-cache.cc:  bitmap_obstack_initialize (&m_bitmaps);
> > >>> gimple-range-gori.cc:  bitmap_obstack_initialize (&m_bitmaps);
> > >>> gimple-range-infer.cc:  bitmap_obstack_initialize (&m_bitmaps);
> > >>> gimple-range-phi.cc:  bitmap_obstack_initialize (&m_bitmaps);
> > >>>
> > >>> or even:
> > >>>
> > >>> $ grep obstack.*NULL *value* *range*
> > >>> value-range-storage.cc:    obstack_free (&m_obstack, NULL);
> > >>> value-relation.cc:  obstack_free (&m_chain_obstack, NULL);
> > >>> value-relation.cc:  obstack_free (&m_chain_obstack, NULL);
> > >>> gimple-range-infer.cc:  obstack_free (&m_list_obstack, NULL);
> > >>> value-range-storage.cc:    obstack_free (&m_obstack, NULL);
> > >>>
> > >>> I'm obviously missing something here.
> > >>
> > >> Look for BITMAP_ALLOC (NULL) in the backtrace in the PR
> > >
> > > Ahh!  Thanks.
> > >
> > > A few default obstack uses snuck in while I wasn't looking.
> > >
> > > $ grep BITMAP_ALLOC.*NULL *range*
> > > gimple-range-cache.cc:  m_propfail = BITMAP_ALLOC (NULL);
> > > gimple-range-cache.h:  inline ssa_lazy_cache () { active_p =
> > > BITMAP_ALLOC (NULL); }
> > > gimple-range.cc:  m_pop_list = BITMAP_ALLOC (NULL);
> > >
> > > I wonder if it would be cleaner to just change these to use named obstacks.
> >
> > I didn’t find any obvious obstack to use, but sure.  This was the easiest fix ;)
> >
> > Richard
> >
> > > Andrew, is there a reason we were using the default obstack for these?
> > > For reference, they are  class update_list used in the ranger cache,
> > > ssa_lazy_cache, and dom_ranger.
> > >
> > > Aldy
> > >
> >
> 
> 

-- 
Richard Biener <rguenther@suse.de>
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