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

[Richard Biener <rguenther@suse.de>]

> 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

Richard 


> Aldy
>