1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
|
(***********************************************************************)
(* *)
(* OCaml *)
(* *)
(* Xavier Leroy, projet Gallium, INRIA Rocquencourt *)
(* *)
(* Copyright 2014 Institut National de Recherche en Informatique et *)
(* en Automatique. All rights reserved. This file is distributed *)
(* under the terms of the Q Public License version 1.0. *)
(* *)
(***********************************************************************)
(* Dead code elimination: remove pure instructions whose results are
not used. *)
open Mach
(* [deadcode i] returns a pair of an optimized instruction [i']
and a set of registers live "before" instruction [i]. *)
let rec deadcode i =
match i.desc with
| Iend | Ireturn | Iop(Itailcall_ind) | Iop(Itailcall_imm _) | Iraise _ ->
(i, Reg.add_set_array i.live i.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 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)
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)
| 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)
| Iloop(body) ->
let (body', _) = deadcode body in
let (s, _) = deadcode i.next in
({i with desc = Iloop body'; next = s}, i.live)
| Icatch(nfail, body, handler) ->
let (body', _) = deadcode body in
let (handler', _) = deadcode handler in
let (s, _) = deadcode i.next in
({i with desc = Icatch(nfail, body', handler'); next = s}, i.live)
| Iexit nfail ->
(i, i.live)
| Itrywith(body, handler) ->
let (body', _) = deadcode body in
let (handler', _) = deadcode handler in
let (s, _) = deadcode i.next in
({i with desc = Itrywith(body', handler'); next = s}, i.live)
let fundecl f =
let (new_body, _) = deadcode f.fun_body in
{f with fun_body = new_body}
|
