Re: Continue stmt branch prediction

["Richard Guenther" <richard.guenther@gmail.com>]

On Thu, Feb 14, 2008 at 4:11 PM, Jan Hubicka <jh@suse.cz> wrote:
>
> > Jan Hubicka wrote:
>  > >The prediction is implemented via high level predictors that used also to
>  > >predict,
>  > >for example, that explicit goto statements are not taken (this is helping
>  > >kernel) and can be used for other stuff in other languages too.
>  > >I will re-introduce the other predictors by followups later, this patch was
>  > >developed while looking into the gzip regression as predicting continue
>  > >formed
>  > >
>  >
>  > What are the other predictors?  It might help to understand it better if
>  > we had a better overview of everything PREDICT_EXPR was going to do.
>
>  I was mostly looking into following stuff:
>   1) the continue bit
>   2) explicit goto statements are usually not executed
>   3) default path of C switch statement on emum with all named fields
>   explicit is unlikely
>   4) expanded bounds checks (ie arrays tends to be in bounds. We used to
>   have PRED_MUDLFAP here but it was dropped and Java has similar logic)
>   5) expanded openMP constructs
>   6) higher level constructs from non-C frontends we have.  There are
>   cases where we produce control flow expanding stuff like fortran
>   vectors where we have unlikely paths through. Though I didn't look
>   into great detail into this yet.
>
>  We already handle same way the calls to noreturn functions and functions
>  marked via cold attribute, but those are easilly recognized on gimple
>  and don't need extra marker.

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.

Richard.