%%
%% %CopyrightBegin%
%%
%% Copyright Ericsson AB 2008-2013. 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 ->
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([{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).
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([], _) -> [].
