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
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
|
%%
%% %CopyrightBegin%
%%
%% Copyright Ericsson AB 2008-2013. All Rights Reserved.
%%
%% Licensed under the Apache License, Version 2.0 (the "License");
%% you may not use this file except in compliance with the License.
%% You may obtain a copy of the License at
%%
%% http://www.apache.org/licenses/LICENSE-2.0
%%
%% Unless required by applicable law or agreed to in writing, software
%% distributed under the License is distributed on an "AS IS" BASIS,
%% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
%% See the License for the specific language governing permissions and
%% limitations under the License.
%%
%% %CopyrightEnd%
%%
-module(beam_peep).
-export([module/2]).
-import(lists, [reverse/1,member/2]).
module({Mod,Exp,Attr,Fs0,_}, _Opts) ->
%% First coalesce adjacent labels.
{Fs1,Lc} = beam_clean:clean_labels(Fs0),
%% Do the peep hole optimizations.
Fs = [function(F) || F <- Fs1],
{ok,{Mod,Exp,Attr,Fs,Lc}}.
function({function,Name,Arity,CLabel,Is0}) ->
try
Is1 = peep(Is0),
Is = beam_jump:remove_unused_labels(Is1),
{function,Name,Arity,CLabel,Is}
catch
Class:Error ->
Stack = erlang:get_stacktrace(),
io:fwrite("Function: ~w/~w\n", [Name,Arity]),
erlang:raise(Class, Error, Stack)
end.
%% Peep-hole optimizations suitable to perform when most of the
%% optimations passes have been run.
%%
%% (1) In a sequence of tests, we can remove any test instruction
%% that has been previously seen, because it will certainly
%% succeed.
%%
%% For instance, in the following code sequence
%%
%% is_eq_exact _Fail SomeRegister SomeLiteral
%% is_ne_exact _Fail SomeOtherRegister SomeOtherLiteral
%% is_eq_exact _Fail SomeRegister SomeLiteral
%% is_ne_exact _Fail SomeOtherRegister StillSomeOtherLiteral
%%
%% the third test is redundant. The code sequence will be produced
%% by a combination of semicolon and command guards, such as
%%
%% InEncoding =:= latin1, OutEncoding =:= unicode;
%% InEncoding =:= latin1, OutEncoding =:= utf8 ->
%%
peep(Is) ->
peep(Is, gb_sets:empty(), []).
peep([{bif,tuple_size,_,[_]=Ops,Dst}=I|Is], SeenTests0, Acc) ->
%% Pretend that we have seen {test,is_tuple,_,Ops}.
SeenTests1 = gb_sets:add({is_tuple,Ops}, SeenTests0),
%% Kill all remembered tests that depend on the destination register.
SeenTests = kill_seen(Dst, SeenTests1),
peep(Is, SeenTests, [I|Acc]);
peep([{bif,_,_,_,Dst}=I|Is], SeenTests0, Acc) ->
%% Kill all remembered tests that depend on the destination register.
SeenTests = kill_seen(Dst, SeenTests0),
peep(Is, SeenTests, [I|Acc]);
peep([{gc_bif,_,_,_,_,Dst}=I|Is], SeenTests0, Acc) ->
%% Kill all remembered tests that depend on the destination register.
SeenTests = kill_seen(Dst, SeenTests0),
peep(Is, SeenTests, [I|Acc]);
peep([{jump,{f,L}},{label,L}=I|Is], _, Acc) ->
%% Sometimes beam_jump has missed this optimization.
peep(Is, gb_sets:empty(), [I|Acc]);
peep([{select,Op,R,F,Vls0}|Is], _, Acc) ->
case prune_redundant_values(Vls0, F) of
[] ->
%% No values left. Must convert to plain jump.
I = {jump,F},
peep(Is, gb_sets:empty(), [I|Acc]);
[_|_]=Vls ->
I = {select,Op,R,F,Vls},
peep(Is, gb_sets:empty(), [I|Acc])
end;
peep([{test,Op,_,Ops}=I|Is], SeenTests0, Acc) ->
case beam_utils:is_pure_test(I) of
false ->
%% Bit syntax matching, which may modify registers and/or
%% match state. Clear all information about tests that
%% has succeeded.
peep(Is, gb_sets:empty(), [I|Acc]);
true ->
case is_test_redundant(Op, Ops, SeenTests0) of
true ->
%% This test or a similar test has already succeeded and
%% is therefore redundant.
peep(Is, SeenTests0, Acc);
false ->
%% Remember that we have seen this test.
Test = {Op,Ops},
SeenTests = gb_sets:insert(Test, SeenTests0),
peep(Is, SeenTests, [I|Acc])
end
end;
peep([I|Is], _, Acc) ->
%% An unknown instruction. Throw away all information we
%% have collected about test instructions.
peep(Is, gb_sets:empty(), [I|Acc]);
peep([], _, Acc) -> reverse(Acc).
is_test_redundant(Op, Ops, Seen) ->
gb_sets:is_element({Op,Ops}, Seen) orelse
is_test_redundant_1(Op, Ops, Seen).
is_test_redundant_1(is_boolean, [R], Seen) ->
gb_sets:is_element({is_eq_exact,[R,{atom,false}]}, Seen) orelse
gb_sets:is_element({is_eq_exact,[R,{atom,true}]}, Seen);
is_test_redundant_1(_, _, _) -> false.
kill_seen(Dst, Seen0) ->
gb_sets:from_ordset(kill_seen_1(gb_sets:to_list(Seen0), Dst)).
kill_seen_1([{_,Ops}=Test|T], Dst) ->
case member(Dst, Ops) of
true -> kill_seen_1(T, Dst);
false -> [Test|kill_seen_1(T, Dst)]
end;
kill_seen_1([], _) -> [].
prune_redundant_values([_Val,F|Vls], F) ->
prune_redundant_values(Vls, F);
prune_redundant_values([Val,Lbl|Vls], F) ->
[Val,Lbl|prune_redundant_values(Vls, F)];
prune_redundant_values([], _) -> [].
|
