Re: [PATCH] Fix inaccurate estimation of probabilities in the scheduler

[Vladimir Makarov <vmakarov at redhat dot com>]

Andrey Belevantsev wrote:

> Hello,
>
> This patch fixes inaccurate calculation of basic block execution 
> probabilities in the scheduler. The old code assumed the probability 
> of leaving a loop as 10%, and distributed the rest evenly among all 
> other outgoing edges. The patch fixes this by using frequency field of 
> basic block structure, either when branch guessing is working or 
> profile information is available.
>
> The patch also introduces two parameters instead of hard-coded 
> scheduler values. These are maximal latency of the instruction, which 
> is to be considered for interblock code motion, and minimal relative 
> basic block probability. The default values are 3 and 40%, respectively.
>
> The patch also sets these parameters to 2 and 20% for IA-64 platform. 
> These settings were chosen as the best one during SPEC testing done 
> back in March. That time, the change was practically neutral with 
> exception of bzip2, which had 2,7% speedup at -O2. I was going to redo 
> the tests with the mainline, but unfortunately, gcc and galgel do not 
> work on ia64 as of June 29 mainline. I can either submit these values 
> or redo the tests and send the new values as a followup.
>
> Bootstrapped and regtested on i686-linux and ia64-linux. Bootstrap 
> times practically haven't changed.
>
> OK for mainline?
Next time if you need an approval, please put RFA in the subject.  As I 
know you need a copyright assignment in order to commit your patch (and 
probably futiure patches) into gcc.  Please get it first.  You can find 
information how to do it on gcc mailing lists.

As for the patch.  In general it is ok.  Finaly, haifa scheduler will 
use gcc infrastracture for the frequencies.

Although I have some minor remarks

o You missed changelog entry for your patch.
o I think it is better use word scheduler in "historic evaluation" 
instead of historic.
o You should always put two blanks after the end of sentence (after the 
period).  It is requirement of Gnu coding standard.
o You don't need to put one statement in {}.
o Some comment lines are 80-char length.  It is better to use maximum 79 
characters on a line.

When you get the copyright assignment, please submit the patch again 
(with changes I mentioned above) and I'll commit the patch into mainline 
because, as I see, you have no write access to the repository.

And thanks for the patch.

Vlad