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(* getreg2.sml
*
* COPYRIGHT (c) 1996 Bell Laboratories.
*
*)
(** A simple first come/first serve register allocator **)
functor GetReg2(val first : int (* start from ``first'' *)
val nRegs : int (* n registers *)
val available : int list) : GETREG =
struct
exception GetReg
val size = first+nRegs
val allRegs = Array.array(size,false)
val preferred = Array.array(size,~1)
fun reset () = Array.modify(fn _ => ~1) preferred
val _ = app (fn r => Array.update(allRegs,r,true)) available
fun getreg{pref,stamp:int,proh} =
let (* use preferred registers whenever possible *)
fun checkPreferred [] = find(first)
| checkPreferred(r::rs) =
if Array.sub(proh,r) <> stamp andalso
Array.sub(allRegs,r) then r
else checkPreferred rs
and find(start) =
let val limit = Array.length allRegs
fun search r =
if Array.sub(proh,r) <> stamp andalso
Array.sub(allRegs,r) then r
else let val r = r+1
in if r >= limit then raise GetReg else search r
end
in search start
end
in checkPreferred pref end
fun getpair{pref,stamp:int,proh} = raise GetReg (* unimplemented *)
end
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