Dominators question

Dominators question

[Andrew MacLeod]

When something like the loop unswitching code adds elements to the CFGs, 
does this invalidate the dominators? or are they updated?  or is it in 
an in between state.

Im curious because a) the relation code uses it under the covers, and b) 
Im looking to add a ranger caching improvement which also uses 
dominators if they are available.

When blocks are added, I wonder what will happen to

   1) dom_info_available_p (CDI_DOMINATORS)  (is it still true), and 
then what happens to

   2) get_immediate_dominator (CDI_DOMINATORS, bb);  for one of the 
newly added BBs.

Thanks

Andrew

Re: Dominators question

[Richard Biener]

On December 3, 2021 3:15:25 PM GMT+01:00, Andrew MacLeod <amacleod@redhat.com> wrote:
>When something like the loop unswitching code adds elements to the CFGs, 
>does this invalidate the dominators? or are they updated?  or is it in 
>an in between state.
>
>Im curious because a) the relation code uses it under the covers, and b) 
>Im looking to add a ranger caching improvement which also uses 
>dominators if they are available.
>
>When blocks are added, I wonder what will happen to
>
>   1) dom_info_available_p (CDI_DOMINATORS)  (is it still true), and 
>then what happens to
>
>   2) get_immediate_dominator (CDI_DOMINATORS, bb);  for one of the 
>newly added BBs.

Dominators are generally updated by most high level CFG manipulations, just the fast queries are invalidated. If a pass uses CFG manipulation that does not update dominators you will get ICEs or silent wron code... 

Richard. 

>Thanks
>
>Andrew
>

Re: Dominators question

[Andrew MacLeod]

On 12/3/21 11:46, Richard Biener wrote:
> On December 3, 2021 3:15:25 PM GMT+01:00, Andrew MacLeod <amacleod@redhat.com> wrote:
>> When something like the loop unswitching code adds elements to the CFGs,
>> does this invalidate the dominators? or are they updated?  or is it in
>> an in between state.
>>
>> Im curious because a) the relation code uses it under the covers, and b)
>> Im looking to add a ranger caching improvement which also uses
>> dominators if they are available.
>>
>> When blocks are added, I wonder what will happen to
>>
>>    1) dom_info_available_p (CDI_DOMINATORS)  (is it still true), and
>> then what happens to
>>
>>    2) get_immediate_dominator (CDI_DOMINATORS, bb);  for one of the
>> newly added BBs.
> Dominators are generally updated by most high level CFG manipulations, just the fast queries are invalidated. If a pass uses CFG manipulation that does not update dominators you will get ICEs or silent wron code...
>
> Richard.
>
Are post dominators generally available as well?  ie, does the presence 
of one imply the other?  or do I need to call calculate_dominance _info 
with CDI_POST_DOMINATORS?

Thanks

Andrew

Re: Dominators question

[Jeff Law]

On 12/14/2021 12:51 PM, Andrew MacLeod via Gcc-patches wrote:
> On 12/3/21 11:46, Richard Biener wrote:
>> On December 3, 2021 3:15:25 PM GMT+01:00, Andrew MacLeod 
>> <amacleod@redhat.com> wrote:
>>> When something like the loop unswitching code adds elements to the 
>>> CFGs,
>>> does this invalidate the dominators? or are they updated?  or is it in
>>> an in between state.
>>>
>>> Im curious because a) the relation code uses it under the covers, 
>>> and b)
>>> Im looking to add a ranger caching improvement which also uses
>>> dominators if they are available.
>>>
>>> When blocks are added, I wonder what will happen to
>>>
>>>    1) dom_info_available_p (CDI_DOMINATORS)  (is it still true), and
>>> then what happens to
>>>
>>>    2) get_immediate_dominator (CDI_DOMINATORS, bb);  for one of the
>>> newly added BBs.
>> Dominators are generally updated by most high level CFG 
>> manipulations, just the fast queries are invalidated. If a pass uses 
>> CFG manipulation that does not update dominators you will get ICEs or 
>> silent wron code...
>>
>> Richard.
>>
> Are post dominators generally available as well?  ie, does the 
> presence of one imply the other?  or do I need to call 
> calculate_dominance _info with CDI_POST_DOMINATORS?
They're built and maintained separately.

jeff