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Liveness and Deadcode refactoring (#670)

master
Mark Shinwell 2016-07-07 10:15:36 +01:00 committed by GitHub
parent 9d77b268ed
commit 5af8dc6ad6
2 changed files with 13 additions and 11 deletions
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11
asmcomp/deadcode.ml
View File

@ -22,32 +22,33 @@ open Mach
and a set of registers live "before" instruction [i]. *)
let rec deadcode i =
let arg = i.arg in
match i.desc with
| Iend | Ireturn | Iop(Itailcall_ind _) | Iop(Itailcall_imm _) | Iraise _ ->
(i, Reg.add_set_array i.live i.arg)
(i, Reg.add_set_array i.live arg)
| Iop op ->
let (s, before) = deadcode i.next in
if Proc.op_is_pure op (* no side effects *)
&& Reg.disjoint_set_array before i.res (* results are not used after *)
&& not (Proc.regs_are_volatile i.arg) (* no stack-like hard reg *)
&& not (Proc.regs_are_volatile arg) (* no stack-like hard reg *)
&& not (Proc.regs_are_volatile i.res) (* is involved *)
then begin
assert (Array.length i.res > 0); (* sanity check *)
(s, before)
end else begin
({i with next = s}, Reg.add_set_array i.live i.arg)
({i with next = s}, Reg.add_set_array i.live arg)
end
| Iifthenelse(test, ifso, ifnot) ->
let (ifso', _) = deadcode ifso in
let (ifnot', _) = deadcode ifnot in
let (s, _) = deadcode i.next in
({i with desc = Iifthenelse(test, ifso', ifnot'); next = s},
Reg.add_set_array i.live i.arg)
Reg.add_set_array i.live arg)
| Iswitch(index, cases) ->
let cases' = Array.map (fun c -> fst (deadcode c)) cases in
let (s, _) = deadcode i.next in
({i with desc = Iswitch(index, cases'); next = s},
Reg.add_set_array i.live i.arg)
Reg.add_set_array i.live arg)
| Iloop(body) ->
let (body', _) = deadcode body in
let (s, _) = deadcode i.next in

13
asmcomp/liveness.ml
View File

@ -35,18 +35,19 @@ let rec live i finally =
before the instruction sequence.
The instruction i is annotated by the set of registers live across
the instruction. *)
let arg = i.arg in
match i.desc with
Iend ->
i.live <- finally;
finally
| Ireturn | Iop(Itailcall_ind _) | Iop(Itailcall_imm _) ->
i.live <- Reg.Set.empty; (* no regs are live across *)
Reg.set_of_array i.arg
Reg.set_of_array arg
| Iop op ->
let after = live i.next finally in
if Proc.op_is_pure op (* no side effects *)
&& Reg.disjoint_set_array after i.res (* results are not used after *)
&& not (Proc.regs_are_volatile i.arg) (* no stack-like hard reg *)
&& not (Proc.regs_are_volatile arg) (* no stack-like hard reg *)
&& not (Proc.regs_are_volatile i.res) (* is involved *)
then begin
(* This operation is dead code. Ignore its arguments. *)
@ -66,13 +67,13 @@ let rec live i finally =
| _ ->
across_after in
i.live <- across;
Reg.add_set_array across i.arg
Reg.add_set_array across arg
end
| Iifthenelse(_test, ifso, ifnot) ->
let at_join = live i.next finally in
let at_fork = Reg.Set.union (live ifso at_join) (live ifnot at_join) in
i.live <- at_fork;
Reg.add_set_array at_fork i.arg
Reg.add_set_array at_fork arg
| Iswitch(_index, cases) ->
let at_join = live i.next finally in
let at_fork = ref Reg.Set.empty in
@ -80,7 +81,7 @@ let rec live i finally =
at_fork := Reg.Set.union !at_fork (live cases.(i) at_join)
done;
i.live <- !at_fork;
Reg.add_set_array !at_fork i.arg
Reg.add_set_array !at_fork arg
| Iloop(body) ->
let at_top = ref Reg.Set.empty in
(* Yes, there are better algorithms, but we'll just iterate till
@ -120,7 +121,7 @@ let rec live i finally =
before_body
| Iraise _ ->
i.live <- !live_at_raise;
Reg.add_set_array !live_at_raise i.arg
Reg.add_set_array !live_at_raise arg
let reset () =
live_at_raise := Reg.Set.empty;