aboutsummaryrefslogtreecommitdiffstats
path: root/lib/compiler/src/beam_peep.erl
blob: a199aa50ed3e3e5e8a0c3ff077c60bfcdde180e9 (plain) (blame)
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
%%
%% %CopyrightBegin%
%%
%% Copyright Ericsson AB 2008-2010. All Rights Reserved.
%%
%% The contents of this file are subject to the Erlang Public License,
%% Version 1.1, (the "License"); you may not use this file except in
%% compliance with the License. You should have received a copy of the
%% Erlang Public License along with this software. If not, it can be
%% retrieved online at http://www.erlang.org/.
%%
%% Software distributed under the License is distributed on an "AS IS"
%% basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
%% the License for the specific language governing rights 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 ->
%%
%% (2) A select_val/4 instruction that only verifies that
%%     its argument is either 'true' or 'false' can be
%%     be replaced with an is_boolean/2 instruction. That is:
%%
%%          select_val Reg Fail   [ true Next false Next ]
%%        Next: ...
%%         
%%     can be rewritten to
%%
%%          is_boolean Fail Reg
%%        Next: ...
%%

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([{test,is_boolean,{f,Fail},Ops}|_]=Is, SeenTests,
     [{test,is_atom,{f,Fail},Ops}|Acc]) ->
    %% The previous is_atom/2 test (with the same failure label) is redundant.
    %% (If is_boolean(Src) is true, is_atom(Src) is also true, so it is
    %% OK to still remember that we have seen is_atom/1.)
    peep(Is, SeenTests, Acc);
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 ->
	    Test = {Op,Ops},
	    case gb_sets:is_element(Test, SeenTests0) of
		true ->
		    %% This test has already succeeded and
		    %% is therefore redundant.
		    peep(Is, SeenTests0, Acc);
		false ->
		    %% Remember that we have seen this test.
		    SeenTests = gb_sets:insert(Test, SeenTests0),
		    peep(Is, SeenTests, [I|Acc])
	    end
    end;
peep([{select,select_val,Src,Fail,
       [{atom,false},{f,L},{atom,true},{f,L}]}|
      [{label,L}|_]=Is], SeenTests, Acc) ->
    I = {test,is_boolean,Fail,[Src]},
    peep([I|Is], SeenTests, Acc);
peep([{select,select_val,Src,Fail,
       [{atom,true},{f,L},{atom,false},{f,L}]}|
      [{label,L}|_]=Is], SeenTests, Acc) ->
    I = {test,is_boolean,Fail,[Src]},
    peep([I|Is], SeenTests, Acc);
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).

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([], _) -> [].