Re: CFG merge part 7 - superblock/trace scheduling

[Jan Hubicka <jh at suse dot cz>]

> Hi,
> This patch adds option to enable superblock scheduling (aka EBB scheduler) for
> non-IA-64 targets as well as "trace scheduling" (aka EBB scheduler preceeded by
> the trace formation).
> My experience with this feature are bit mixed - by default it causes 2%
> regression on Athlon.  By significantly improving MD description I was able to

This regression seems to go away after changing the superblock choice
algorithm I sent in merge patch 11.
> get about 0.3%/0.8% speedup on Specint/Specfp, that is about the 1/3rd of
> effect of scheduling overall on this target.  I hope I will have time to
> cleanup and send this part soon too as well.  The improvements are noticeable
> in local scheduler as well, but since the basic blocks are small they are much
> less visible.
> --- 3495,3516 ----
>   
>         split_all_insns (1);
>   
> !       if (flag_sched2_use_superblocks || flag_sched2_use_traces)
> ! 	{
> !  	  if (!flag_sched2_use_traces)
> ! 	    reorder_basic_blocks ();
> ! 	  else
> ! 	    tracer ();
> ! 	  cleanup_cfg (CLEANUP_EXPENSIVE | CLEANUP_UPDATE_LIFE);
> ! 	  schedule_ebbs (rtl_dump_file);
> ! 	  /* No liveness updating code yet, but it should be easy to do  */
> ! 	  count_or_remove_death_notes (NULL, 1);
> ! 	  life_analysis (get_insns (), rtl_dump_file, PROP_DEATH_NOTES);
> ! 	  cleanup_cfg (CLEANUP_EXPENSIVE | CLEANUP_UPDATE_LIFE
> ! 		       | (flag_crossjumping ? CLEANUP_CROSSJUMP : 0));
> ! 	}
> !       else
> !         schedule_insns (rtl_dump_file);

We've chatted briefly about this.  Should I change it to move
reorder_basic_block pass in front of sched2 pass and re-do
reordering only in case we did eigher some cleanup_cfg or reg-stack
conversion?
Since trace scheduling can make blocks to be empty, it is not that
incommon that cleanup_cfg match after it.  I am not quite sure that this
is desirable at all.  Perhaps we can avoid any cfg_cleanup post
scheduling and do it only for i386 reg-stack where we do have pass
ordering problem?

It results in bigger binaries and don't help for Athlon, but on in-order
architectures this may be different.

Honza