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
