[Haifa Scheduler] Fix latent bug in macro-fusion/instruction grouping

[Jeff Law]

On 02/06/15 05:24, James Greenhalgh wrote:
>
> ---
> 2015-02-06  James Greenhalgh  <james.greenhalgh@arm.com>
>
> 	* haifa-sched.c (recompute_todo_spec): After applying a
> 	replacement and cancelling a dependency, also clear the
> 	SCHED_GROUP_P flag.
My worry here would be that we might be clearing a SCHED_GROUP_P that 
had been set for some reason other than macro-fusion.

It makes me wonder if we really want another bit to carry the "these 
must remain consecutive for correctness" vs "please keep these together 
so something later can optimize better" characteristics.

I'm also tracking a bug where we mis-handle SCHED_GROUP_P when there's a 
hazard of some sort between the first and second in the group.  In that 
case we fire the first insn, then queue the second.  If some other insn 
that had been queued earlier becomes ready during the cycles between 
where the first insn fired and 2nd insn is scheduled to fire, then we'll 
break the SCHED_GROUP_P relationship.  For the particular case I'm 
looking at, it's a correctness issue (cc0 machine and we end up 
splitting the cc0-setter and cc0-user).


Jeff