diff options
| -rw-r--r-- | lib/compiler/src/beam_dead.erl | 71 |
1 files changed, 48 insertions, 23 deletions
diff --git a/lib/compiler/src/beam_dead.erl b/lib/compiler/src/beam_dead.erl index f57bed0658..901ef5dc39 100644 --- a/lib/compiler/src/beam_dead.erl +++ b/lib/compiler/src/beam_dead.erl @@ -101,39 +101,56 @@ forward([{bif,_,_,_,_}=Bif|[{label,L}|_]=Is], D, Lc, Acc) -> forward([{select,select_val,Reg,_,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). - Key = {Lbl,Dst}, - Block = case D of - #{Key := 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 maps:find({Lbl,Dst}, D) of - {ok,Lit} -> Is1; %Safe to remove move instruction. - _ -> Is0 %Keep move instruction. - end, - forward(Is, D, Lc, [LblI|Acc]); -forward([{test,_,_,_}=I|Is]=Is0, D, Lc, Acc) -> +forward([{label,Lbl},{block,[{set,[Dst],[Lit],move}|BlkIs]}=Blk0|Is], + D, Lc, Acc0) -> + Acc = [{label,Lbl}|Acc0], + case already_has_value(Lit, Lbl, Dst, D) andalso + no_fallthrough(Acc0) of + true -> + Blk = {block,BlkIs}, + forward([Blk|Is], D, Lc, Acc); + false -> + forward([Blk0|Is], D, Lc, Acc) + end; +forward([{label,Lbl},{move,Lit,Dst}=Move|Is], D, Lc, Acc0) -> + Acc = [{label,Lbl}|Acc0], + case already_has_value(Lit, Lbl, Dst, D) andalso + no_fallthrough(Acc0) of + true -> + %% Remove redundant 'move' instruction. + forward(Is, D, Lc, Acc); + false -> + %% Keep 'move' instruction. + forward([Move|Is], D, Lc, Acc) + end; +forward([{test,_,_,_}=I|Is]=Is0, D0, Lc, Acc) -> %% Help the second, backward pass to by inserting labels after %% relational operators so that they can be skipped if they are %% known to be true. + D = update_unsafe_labels(I, D0), case useful_to_insert_label(Is0) of false -> forward(Is, D, Lc, [I|Acc]); true -> forward(Is, D, Lc+1, [{label,Lc},I|Acc]) end; -forward([I|Is], D, Lc, Acc) -> +forward([I|Is], D0, Lc, Acc) -> + D = update_unsafe_labels(I, D0), forward(Is, D, Lc, [I|Acc]); forward([], _, Lc, Acc) -> {Acc,Lc}. +no_fallthrough([I|_]) -> + beam_jump:is_unreachable_after(I). + +already_has_value(Lit, Lbl, Reg, D) -> + Key = {Lbl,Reg}, + case D of + #{Lbl:=unsafe} -> + false; + #{Key:=Lit} -> + true; + #{} -> + false + end. + update_value_dict([Lit,{f,Lbl}|T], Reg, D0) -> Key = {Lbl,Reg}, D = case D0 of @@ -144,6 +161,14 @@ update_value_dict([Lit,{f,Lbl}|T], Reg, D0) -> update_value_dict(T, Reg, D); update_value_dict([], _, D) -> D. +update_unsafe_labels(I, D) -> + Ls = beam_jump:instr_labels(I), + update_unsafe_labels_1(Ls, D). + +update_unsafe_labels_1([L|Ls], D) -> + update_unsafe_labels_1(Ls, D#{L=>unsafe}); +update_unsafe_labels_1([], D) -> D. + useful_to_insert_label([_,{label,_}|_]) -> false; useful_to_insert_label([{test,Op,_,_}|_]) -> |