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

[Richard Biener <richard.guenther@gmail.com>]

> 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
>