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Diffstat (limited to 'lib/compiler/src/beam_peep.erl')
| -rw-r--r-- | lib/compiler/src/beam_peep.erl | 191 |
1 files changed, 191 insertions, 0 deletions
diff --git a/lib/compiler/src/beam_peep.erl b/lib/compiler/src/beam_peep.erl new file mode 100644 index 0000000000..d03ac4b1f4 --- /dev/null +++ b/lib/compiler/src/beam_peep.erl @@ -0,0 +1,191 @@ +%% +%% %CopyrightBegin% +%% +%% Copyright Ericsson AB 2008-2009. 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) Code like +%% +%% is_ne_exact Fail Reg Literal1 +%% is_ne_exact Fail Reg Literal2 +%% is_ne_exact Fail Reg Literal3 +%% is_eq_exact UltimateFail Reg Literal4 +%% Fail: .... +%% +%% can be rewritten to +%% +%% select_val Reg UltimateFail [ Literal1 Fail +%% Literal2 Fail +%% Literal3 Fail +%% Literal4 Fail ] +%% +%% (3) 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), + make_select_val(I, Is, SeenTests, Acc) + end + end; +peep([{select_val,Src,Fail, + {list,[{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_val,Src,Fail, + {list,[{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). + +make_select_val({test,is_ne_exact,{f,Fail},[Val,Lit]}=I0, + Is0, SeenTests, Acc) -> + try + Type = case Lit of + {atom,_} -> atom; + {integer,_} -> integer; + _ -> throw(impossible) + end, + {I,Is} = make_select_val_1(Is0, Fail, Val, Type, [Lit,{f,Fail}]), + peep([I|Is], SeenTests, Acc) + catch + impossible -> + peep(Is0, SeenTests, [I0|Acc]) + end; +make_select_val(I, Is, SeenTests, Acc) -> + peep(Is, SeenTests, [I|Acc]). + +make_select_val_1([{test,is_ne_exact,{f,Fail},[Val,{Type,_}=Lit]}|Is], + Fail, Val, Type, Acc) -> + make_select_val_1(Is, Fail, Val, Type, [Lit,{f,Fail}|Acc]); +make_select_val_1([{test,is_eq_exact,{f,UltimateFail},[Val,{Type,_}=Lit]} | + [{label,Fail}|_]=Is], Fail, Val, Type, Acc) -> + Choices = [Lit,{f,Fail}|Acc], + I = {select_val,Val,{f,UltimateFail},{list,Choices}}, + {I,Is}; +make_select_val_1(_Is, _Fail, _Val, _Type, _Acc) -> throw(impossible). + +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([], _) -> []. + + |