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-rw-r--r--lib/compiler/src/beam_dead.erl71
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,_,_}|_]) ->