Re: Generalize ready list sorting via heuristics in rank_for_schedule.

[Maxim Kuvyrkov <mkuvyrkov at ispras dot ru>]

Peter Steinmetz wrote:
> Currently, within the ready_sort macro in haifa-sched.c, the call to qsort
> is passed "rank_for_schedule" to help it decide which of two instructions
> should be placed further towards the front of the ready list.
> Rank_for_schedule uses a set of ordered heuristics (rank, priority, etc.)
> to make this decision.  The set of heuristics is fixed for all target
> machines.
There already are two target hooks specifically for this purpose: 
targetm.sched.{reorder, reorder2}. They both have higher priority, than 
ready_sort ().

> There can be cases, however, where a target machine may want to define
> heuristics driven by specific characteristics of that machine.  Those
> heuristics may be meaningless on other targets.
In rank_for_schedule () only machine independent heuristics are 
gathered; the rest of the haifa scheduler is no less machine dependent, 
than these heuristics are. Machine dependent things are separated in 
reorder hooks (which, btw, are defined on 3 targets only).

--
Maxim