diff options
Diffstat (limited to 'lib/compiler/src/beam_dead.erl')
| -rw-r--r-- | lib/compiler/src/beam_dead.erl | 102 |
1 files changed, 61 insertions, 41 deletions
diff --git a/lib/compiler/src/beam_dead.erl b/lib/compiler/src/beam_dead.erl index 7b4cd814a2..1365f3d20a 100644 --- a/lib/compiler/src/beam_dead.erl +++ b/lib/compiler/src/beam_dead.erl @@ -1,19 +1,19 @@ %% %% %CopyrightBegin% -%% -%% Copyright Ericsson AB 2002-2009. All Rights Reserved. -%% +%% +%% Copyright Ericsson AB 2002-2011. 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% %% @@ -162,14 +162,11 @@ function({function,Name,Arity,CLabel,Is0}, Lc0) -> %% We must split the basic block when we encounter instructions with labels, %% such as catches and BIFs. All labels must be visible outside the blocks. -%% Also remove empty blocks. split_blocks({function,Name,Arity,CLabel,Is0}) -> Is = split_blocks(Is0, []), {function,Name,Arity,CLabel,Is}. -split_blocks([{block,[]}|Is], Acc) -> - split_blocks(Is, Acc); split_blocks([{block,Bl}|Is], Acc0) -> Acc = split_block(Bl, [], Acc0), split_blocks(Is, Acc); @@ -246,30 +243,24 @@ forward([{select_val,Reg,_,{list,List}}=I|Is], D0, Lc, Acc) -> D = update_value_dict(List, Reg, D0), forward(Is, D, Lc, [I|Acc]); forward([{label,Lbl}=LblI,{block,[{set,[Dst],[Lit],move}|BlkIs]}=Blk|Is], D, Lc, Acc) -> + %% Assumption: The target labels in a select_val/3 instruction + %% cannot be reached in any other way than through the select_val/3 + %% instruction (i.e. there can be no fallthrough to such label and + %% it cannot be referenced by, for example, a jump/1 instruction). Block = case gb_trees:lookup({Lbl,Dst}, D) of - {value,Lit} -> - %% The move instruction seems to be redundant, but also make - %% sure that the instruction preceeding the label - %% cannot fall through to the move instruction. - case is_unreachable_after(Acc) of - false -> Blk; %Must keep move instruction. - true -> {block,BlkIs} %Safe to remove move instruction. - end; - _ -> Blk %Keep move instruction. + {value,Lit} -> {block,BlkIs}; %Safe to remove move instruction. + _ -> Blk %Must keep move instruction. end, forward([Block|Is], D, Lc, [LblI|Acc]); forward([{label,Lbl}=LblI|[{move,Lit,Dst}|Is1]=Is0], D, Lc, Acc) -> + %% Assumption: The target labels in a select_val/3 instruction + %% cannot be reached in any other way than through the select_val/3 + %% instruction (i.e. there can be no fallthrough to such label and + %% it cannot be referenced by, for example, a jump/1 instruction). Is = case gb_trees:lookup({Lbl,Dst}, D) of - {value,Lit} -> - %% The move instruction seems to be redundant, but also make - %% sure that the instruction preceeding the label - %% cannot fall through to the move instruction. - case is_unreachable_after(Acc) of - false -> Is0; %Must keep move instruction. - true -> Is1 %Safe to remove move instruction. - end; - _ -> Is0 %Keep move instruction. - end, + {value,Lit} -> Is1; %Safe to remove move instruction. + _ -> Is0 %Keep move instruction. + end, forward(Is, D, Lc, [LblI|Acc]); forward([{test,is_eq_exact,_,[Dst,Src]}=I, {block,[{set,[Dst],[Src],move}|Bl]}|Is], D, Lc, Acc) -> @@ -281,12 +272,12 @@ forward([{test,is_eq_exact,_,[Dst,Src]}=I,{move,Src,Dst}|Is], D, Lc, Acc) -> forward([I|Is], D, Lc, Acc); forward([{test,is_nil,_,[Dst]}=I,{move,nil,Dst}|Is], D, Lc, Acc) -> forward([I|Is], D, Lc, Acc); -forward([{test,is_eq_exact,_,[_,{atom,_}]}=I|Is], D, Lc, [{label,_}|_]=Acc) -> +forward([{test,is_eq_exact,_,_}=I|Is], D, Lc, Acc) -> case Is of [{label,_}|_] -> forward(Is, D, Lc, [I|Acc]); _ -> forward(Is, D, Lc+1, [{label,Lc},I|Acc]) end; -forward([{test,is_ne_exact,_,[_,{atom,_}]}=I|Is], D, Lc, [{label,_}|_]=Acc) -> +forward([{test,is_ne_exact,_,_}=I|Is], D, Lc, Acc) -> case Is of [{label,_}|_] -> forward(Is, D, Lc, [I|Acc]); _ -> forward(Is, D, Lc+1, [{label,Lc},I|Acc]) @@ -299,16 +290,12 @@ update_value_dict([Lit,{f,Lbl}|T], Reg, D0) -> Key = {Lbl,Reg}, D = case gb_trees:lookup(Key, D0) of none -> gb_trees:insert(Key, Lit, D0); %New. - {value,Lit} -> D0; %Already correct. {value,inconsistent} -> D0; %Inconsistent. {value,_} -> gb_trees:update(Key, inconsistent, D0) end, update_value_dict(T, Reg, D); update_value_dict([], _, D) -> D. -is_unreachable_after([I|_]) -> - beam_jump:is_unreachable_after(I). - %%% %%% Scan instructions in reverse execution order and remove dead code. %%% @@ -371,10 +358,10 @@ backward([{test,bs_start_match2,{f,To0},Live,[Src|_]=Info,Dst}|Is], D, Acc) -> To = shortcut_bs_start_match(To0, Src, D), I = {test,bs_start_match2,{f,To},Live,Info,Dst}, backward(Is, D, [I|Acc]); -backward([{test,is_eq_exact=Op,{f,To0},[Reg,{atom,Val}]=Ops}|Is], D, Acc) -> +backward([{test,is_eq_exact,{f,To0},[Reg,{atom,Val}]=Ops}|Is], D, Acc) -> To1 = shortcut_bs_test(To0, Is, D), To = shortcut_fail_label(To1, Reg, Val, D), - I = {test,Op,{f,To},Ops}, + I = combine_eqs(To, Ops, D, Acc), backward(Is, D, [I|Acc]); backward([{test,Op,{f,To0},Ops0}|Is], D, Acc) -> To1 = shortcut_bs_test(To0, Is, D), @@ -394,7 +381,10 @@ backward([{test,Op,{f,To0},Ops0}|Is], D, Acc) -> _Code -> To2 end, - I = {test,Op,{f,To},Ops0}, + I = case Op of + is_eq_exact -> combine_eqs(To, Ops0, D, Acc); + _ -> {test,Op,{f,To},Ops0} + end, backward(Is, D, [I|Acc]); backward([{test,Op,{f,To0},Live,Ops0,Dst}|Is], D, Acc) -> To1 = shortcut_bs_test(To0, Is, D), @@ -519,6 +509,41 @@ bif_to_test(Name, Args, Fail) -> not_possible() -> throw(not_possible). +%% combine_eqs(To, Operands, Acc) -> Instruction. +%% Combine two is_eq_exact instructions or (an is_eq_exact +%% instruction and a select_val instruction) to a select_val +%% instruction if possible. +%% +%% Example: +%% +%% is_eq_exact F1 Reg Lit1 select_val Reg F2 [ Lit1 L1 +%% L1: . Lit2 L2 ] +%% . +%% . ==> +%% . +%% F1: is_eq_exact F2 Reg Lit2 F1: is_eq_exact F2 Reg Lit2 +%% L2: .... L2: +%% +combine_eqs(To, [Reg,{Type,_}=Lit1]=Ops, D, [{label,L1}|_]) + when Type =:= atom; Type =:= integer -> + case beam_utils:code_at(To, D) of + [{test,is_eq_exact,{f,F2},[Reg,{Type,_}=Lit2]}, + {label,L2}|_] when Lit1 =/= Lit2 -> + {select_val,Reg,{f,F2},{list,[Lit1,{f,L1},Lit2,{f,L2}]}}; + [{select_val,Reg,{f,F2},{list,[{Type,_}|_]=List0}}|_] -> + List = remove_from_list(Lit1, List0), + {select_val,Reg,{f,F2},{list,[Lit1,{f,L1}|List]}}; + _Is -> + {test,is_eq_exact,{f,To},Ops} + end; +combine_eqs(To, Ops, _D, _Acc) -> + {test,is_eq_exact,{f,To},Ops}. + +remove_from_list(Lit, [Lit,{f,_}|T]) -> + T; +remove_from_list(Lit, [Val,{f,_}=Fail|T]) -> + [Val,Fail|remove_from_list(Lit, T)]; +remove_from_list(_, []) -> []. %% shortcut_bs_test(TargetLabel, [Instruction], D) -> TargetLabel' %% Try to shortcut the failure label for a bit syntax matching. @@ -564,16 +589,11 @@ count_bits_matched([{test,_,_,_}|Is], SavePoint, Bits) -> count_bits_matched([{bs_save2,Reg,SavePoint}|_], {Reg,SavePoint}, Bits) -> %% The save point we are looking for - we are done. Bits; -count_bits_matched([{bs_save2,_,_}|Is], SavePoint, Bits) -> - %% Another save point - keep counting. - count_bits_matched(Is, SavePoint, Bits); count_bits_matched([_|_], _, Bits) -> Bits. shortcut_bs_pos_used(To, Reg, D) -> shortcut_bs_pos_used_1(beam_utils:code_at(To, D), Reg, D). -shortcut_bs_pos_used_1([{bs_restore2,Reg,_}|_], Reg, _) -> - false; shortcut_bs_pos_used_1([{bs_context_to_binary,Reg}|_], Reg, _) -> false; shortcut_bs_pos_used_1(Is, Reg, D) -> |