Re: Continue stmt branch prediction

[Andrew MacLeod <amacleod@redhat.com>]

Jan Hubicka wrote:
>> Wouldn't it be easier to add a unlikely_goto stmt for all these and translate
>> that to edge probabilities once we build the cfg?  That is, stick the unlikely
>> bit onto the goto stmt instead of having an extra predict_expr floating around.
>>     
>
> We've disucussed this few mails back.  The problem is that if you have
> something like
>
> if (something)
>    something2
>    goto somewhere else
>
> somewhere else:
>    something_else
>
> then after gimplifing we get
>
>
> if (something) goto around
> something2
> somewehre_else
> around:
>
> and goto is gone.  It is really more a property of the some specific
>   
This example doesn't seem right. You've just changed the meaning of the 
'if' in your example... At least the way I read it. you are no longer 
executing 'something2' if 'something' is true, nor executing 'something 
else' on both paths as in the original case. There are too many 
different things you could have meant for me to guess exactly what you 
did mean :-)

I'll try tho :-)

Did you perhaps mean to reverse the condition to if (!something) in the 
latter case?  If so, then you seem to be arguing that since the original 
'if''s code segment contained an explicit GOTO, that the end result is 
we should predict that it is unlikely to be taken, and therefore we 
should predict that the  'if (!something) goto around' branch *will* be 
taken after gimplifying, and that we lose that info.

Is that correct or were you trying to say something else?

Andrew