diff options
Diffstat (limited to 'lib/compiler/src/beam_jump.erl')
| -rw-r--r-- | lib/compiler/src/beam_jump.erl | 55 |
1 files changed, 41 insertions, 14 deletions
diff --git a/lib/compiler/src/beam_jump.erl b/lib/compiler/src/beam_jump.erl index d3a618d211..8b0e3e32f8 100644 --- a/lib/compiler/src/beam_jump.erl +++ b/lib/compiler/src/beam_jump.erl @@ -101,6 +101,10 @@ %%% always keep the label. (beam_clean will remove any unused %%% labels.) %%% +%%% (7) Replace a jump to a return instruction with a return instruction. +%%% Similarly, replace a jump to deallocate + return with those +%%% instructions. +%%% %%% Note: This modules depends on (almost) all branches and jumps only %%% going forward, so that we can remove instructions (including definition %%% of labels) after any label that has not been referenced by the code @@ -150,7 +154,8 @@ function({function,Name,Arity,CLabel,Asm0}, Lc0) -> Asm3 = share(Asm2), Asm4 = move(Asm3), Asm5 = opt(Asm4, CLabel), - Asm = remove_unused_labels(Asm5), + Asm6 = unshare(Asm5), + Asm = remove_unused_labels(Asm6), {{function,Name,Arity,CLabel,Asm},Lc} catch Class:Error:Stack -> @@ -393,14 +398,13 @@ extract_seq_1(_, _) -> no. { entry :: beam_asm:label(), %Entry label (must not be moved). replace :: #{beam_asm:label() := beam_asm:label()}, %Labels to replace. - labels :: cerl_sets:set(), %Set of referenced labels. - index :: beam_utils:code_index() | {lazy,[beam_utils:instruction()]} %Index built lazily only if needed + labels :: cerl_sets:set() %Set of referenced labels. }). opt(Is0, CLabel) -> find_fixpoint(fun(Is) -> Lbls = initial_labels(Is), - St = #st{entry=CLabel,replace=#{},labels=Lbls,index={lazy,Is}}, + St = #st{entry=CLabel,replace=#{},labels=Lbls}, opt(Is, [], St) end, Is0). @@ -425,16 +429,6 @@ opt([{test,_,{f,L}=Lbl,_}=I|[{jump,{f,L}}|_]=Is], Acc, St) -> %% as in the jump that follows -- thus it is not needed. opt(Is, Acc, St) end; -opt([{test,_,{f,L}=Lbl,_}=I|[{label,L}|_]=Is], Acc, St) -> - %% Similar to the above, except we have a fall-through rather than jump - %% Test Label Ops - %% label Label - case beam_utils:is_pure_test(I) of - false -> - opt(Is, [I|Acc], label_used(Lbl, St)); - true -> - opt(Is, Acc, St) - end; opt([{test,Test0,{f,L}=Lbl,Ops}=I|[{jump,To}|Is]=Is0], Acc, St) -> case is_label_defined(Is, L) of false -> @@ -625,6 +619,39 @@ drop_upto_label([{label,_}|_]=Is) -> Is; drop_upto_label([_|Is]) -> drop_upto_label(Is); drop_upto_label([]) -> []. +%% unshare([Instruction]) -> [Instruction]. +%% Replace a jump to a return sequence (a `return` instruction +%% optionally preced by a `deallocate` instruction) with the return +%% sequence. This always saves execution time and may also save code +%% space (depending on the architecture). Eliminating `jump` +%% instructions also gives beam_trim more opportunities to trim the +%% stack. + +unshare(Is) -> + Short = unshare_collect_short(Is, #{}), + unshare_short(Is, Short). + +unshare_collect_short([{label,L},return|Is], Map) -> + unshare_collect_short(Is, Map#{L=>[return]}); +unshare_collect_short([{label,L},{deallocate,_}=D,return|Is], Map) -> + %% `deallocate` and `return` are combined into one instruction by + %% the loader. + unshare_collect_short(Is, Map#{L=>[D,return]}); +unshare_collect_short([_|Is], Map) -> + unshare_collect_short(Is, Map); +unshare_collect_short([], Map) -> Map. + +unshare_short([{jump,{f,F}}=I|Is], Map) -> + case Map of + #{F:=Seq} -> + Seq ++ unshare_short(Is, Map); + #{} -> + [I|unshare_short(Is, Map)] + end; +unshare_short([I|Is], Map) -> + [I|unshare_short(Is, Map)]; +unshare_short([], _Map) -> []. + %% ulbl(Instruction, UsedCerlSet) -> UsedCerlSet' %% Update the cerl_set UsedCerlSet with any function-local labels %% (i.e. not with labels in call instructions) referenced by |