diff options
| -rw-r--r-- | lib/compiler/src/beam_dead.erl | 35 |
1 files changed, 13 insertions, 22 deletions
diff --git a/lib/compiler/src/beam_dead.erl b/lib/compiler/src/beam_dead.erl index bb93110176..135c7757c5 100644 --- a/lib/compiler/src/beam_dead.erl +++ b/lib/compiler/src/beam_dead.erl @@ -246,30 +246,24 @@ 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) -> @@ -306,9 +300,6 @@ update_value_dict([Lit,{f,Lbl}|T], Reg, D0) -> 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. %%% |