Re: [PATCH] Add operators / and * for profile_{count,probability}.

["Martin Liška" <mliska@suse.cz>]

PING^1

On 5/5/22 20:15, Martin Liška wrote:
> On 5/5/22 15:49, Jan Hubicka wrote:
>> Hi,
>>> The patch simplifies usage of the profile_{count,probability} types.
>>>
>>> Patch can bootstrap on x86_64-linux-gnu and survives regression tests.
>>>
>>> Ready to be installed?
>>
>> The reason I intentionally did not add * and / to the original API was
>> to detect situations where values that should be
>> profile_count/profile_probability are stored into integers, since
>> previous code used integers for everything.
>>
>> Having one to add apply_scale made him/her (mostly me :) to think if the
>> value is really just a fixed scale or it it should be better converted
>> to proper data type (count or probability).
>>
>> I guess now we completed the conversion so risk of this creeping in is
>> relatively low and the code indeed looks better.
> 
> Yes, that's my impression as well that the profiling code is quite settled down.
> 
>> It will make it bit
>> harder for me to backport jump threading profile updating fixes I plan
>> for 12.2 but it should not be hard.
> 
> You'll manage ;)
> 
>>> diff --git a/gcc/cfgloopmanip.cc b/gcc/cfgloopmanip.cc
>>> index b4357c03e86..a1ac1146445 100644
>>> --- a/gcc/cfgloopmanip.cc
>>> +++ b/gcc/cfgloopmanip.cc
>>> @@ -563,8 +563,7 @@ scale_loop_profile (class loop *loop, profile_probability p,
>>>  
>>>  	  /* Probability of exit must be 1/iterations.  */
>>>  	  count_delta = e->count ();
>>> -	  e->probability = profile_probability::always ()
>>> -				    .apply_scale (1, iteration_bound);
>>> +	  e->probability = profile_probability::always () / iteration_bound;
>> However this is kind of example of the problem. 
>> iteration_bound is gcov_type so we can get overflow here.
> 
> typedef int64_t gcov_type;
> 
> and apply_scale takes int64_t types as arguments. Similarly the newly added operators,
> so how can that change anything?
> 
>> I guess we want to downgrade iteration_bound since it is always either 0
>> or int.
>>> diff --git a/gcc/tree-switch-conversion.cc b/gcc/tree-switch-conversion.cc
>>> index e14b4e6c94a..cef26a9878e 100644
>>> --- a/gcc/tree-switch-conversion.cc
>>> +++ b/gcc/tree-switch-conversion.cc
>>> @@ -1782,7 +1782,7 @@ switch_decision_tree::analyze_switch_statement ()
>>>        tree high = CASE_HIGH (elt);
>>>  
>>>        profile_probability p
>>> -	= case_edge->probability.apply_scale (1, (intptr_t) (case_edge->aux));
>>> +	= case_edge->probability / ((intptr_t) (case_edge->aux));
>>
>> I think the switch ranges may be also in risk of overflow?
>>
>> We could make operators to accept gcov_type or int64_t.
> 
> As explained, they do.
> 
> Cheers,
> Martin
> 
>>
>> Thanks,
>> Honza
>