Re: Scheduler and GCC CFG

[Jan Hubicka <jh at suse dot cz>]

> >>>>> Jan Hubicka writes:
> 
> Jan> ... it already should be
> Jan> enough to test whether superblock scheduling can bring us something over
> Jan> region based scheduler we have right now.  I tried that on Athlon and
> Jan> the results are mostly random.  This is partly due to exact CPU model
> Jan> (that has improved by DFA now), abd the fact that Athlon is not very
> Jan> sensitive to scheduling.
> 
> 	On the cfg-branch, you run EBB scheduler instead of the
> post-reload region scheduler.  The tracer pass is run before the first
> scheduling pass, so why not run EBB scheduler instead of first scheduling
> pass?  Is this because first scheduling pass is disabled for x86?  I would
Yes, I just wanted to get something working on x86 first and test it.
It is all unfinished, sorry for that.  Soon, I hope, I will have ready
the Athlon model taking into account FIFO in between decoder and
execution units and then I would like to give it another shot.

I don't see any major reason why the EBB scheduling won't work before
reload.  However since traces may get large and it does a lot of
intrablock motion, number of it not necesary, it may increase register
liveness and turn many registers from local to global ones so this needs
experimentation.

Honza
> expect the first scheduling pass to have much more freedom to move
> instructions within the superblocks.
> 
> David