diff options
| -rw-r--r-- | lib/compiler/src/beam_jump.erl | 62 |
1 files changed, 58 insertions, 4 deletions
diff --git a/lib/compiler/src/beam_jump.erl b/lib/compiler/src/beam_jump.erl index 427f605ce2..72bf1e21dd 100644 --- a/lib/compiler/src/beam_jump.erl +++ b/lib/compiler/src/beam_jump.erl @@ -291,13 +291,14 @@ extract_seq_1(_, _) -> no. { entry :: beam_asm:label(), %Entry label (must not be moved). mlbl :: #{beam_asm:label() := [beam_asm:label()]}, %Moved labels. - labels :: cerl_sets:set() %Set of referenced labels. + labels :: cerl_sets:set(), %Set of referenced labels. + index :: beam_utils:code_index() | {lazy,[beam_utils:instruction()]} %Index build lazily only if needed }). opt(Is0, CLabel) -> find_fixpoint(fun(Is) -> Lbls = initial_labels(Is), - St = #st{entry=CLabel,mlbl=#{},labels=Lbls}, + St = #st{entry=CLabel,mlbl=#{},labels=Lbls,index={lazy,Is}}, opt(Is, [], St) end, Is0). @@ -307,7 +308,7 @@ find_fixpoint(OptFun, Is0) -> Is -> find_fixpoint(OptFun, Is) end. -opt([{test,_,{f,L}=Lbl,_}=I|[{jump,{f,L}}|_]=Is], Acc, St) -> +opt([{test,_,{f,L}=Lbl,_}=I|[{jump,{f,L}}|_]=Is], Acc0, St0) -> %% We have %% Test Label Ops %% jump Label @@ -316,10 +317,23 @@ opt([{test,_,{f,L}=Lbl,_}=I|[{jump,{f,L}}|_]=Is], Acc, St) -> case beam_utils:is_pure_test(I) of false -> %% Test is not pure; we must keep it. - opt(Is, [I|Acc], label_used(Lbl, St)); + opt(Is, [I|Acc0], label_used(Lbl, St0)); true -> %% The test is pure and its failure label is the same %% as in the jump that follows -- thus it is not needed. + %% Check if any of the previous instructions could also be eliminated. + {Acc,St} = opt_useless_loads(Acc0, L, St0), + opt(Is, Acc, St) + end; +opt([{test,_,{f,L}=Lbl,_}=I|[{label,L}|_]=Is], Acc0, St0) -> + %% 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|Acc0], label_used(Lbl, St0)); + true -> + {Acc,St} = opt_useless_loads(Acc0, L, St0), opt(Is, Acc, St) end; opt([{test,Test0,{f,L}=Lbl,Ops}=I|[{jump,To}|Is]=Is0], Acc, St) -> @@ -398,6 +412,46 @@ insert_fc_labels([{label,L}=I|Is0], Mlbl) -> end; insert_fc_labels([_|_]=Is, _) -> Is. +%% After eliminating a test, it might happen, that a register was only used +%% in this test. Let's check if that was the case and if it was so, we can +%% eliminate the load into the register completely. +opt_useless_loads([{block,_}|_]=Is, L, #st{index={lazy,FIs}}=St) -> + opt_useless_loads(Is, L, St#st{index=beam_utils:index_labels(FIs)}); +opt_useless_loads([{block,Block0}|Is], L, #st{index=Index}=St) -> + case opt_useless_block_loads(Block0, L, Index) of + [] -> + opt_useless_loads(Is, L, St); + [_|_]=Block -> + {[{block,Block}|Is],St} + end; +%% After eliminating the test and useless blocks, it might happen, +%% that the previous test could also be eliminated. +%% It might be that the label was already marked as used, even if ultimately, +%% it never will be - we can't do much about it at that point, though +opt_useless_loads([{test,_,{f,L},_}=I|Is], L, St) -> + case beam_utils:is_pure_test(I) of + false -> + {[I|Is],St}; + true -> + opt_useless_loads(Is, L, St) + end; +opt_useless_loads(Is, _L, St) -> + {Is,St}. + +opt_useless_block_loads([{set,[Dst],_,_}=I|Is], L, Index) -> + BlockJump = [{block,Is},{jump,{f,L}}], + case beam_utils:is_killed(Dst, BlockJump, Index) of + true -> + %% The register is killed and not used, we can remove the load + opt_useless_block_loads(Is, L, Index); + false -> + [I|opt_useless_block_loads(Is, L, Index)] + end; +opt_useless_block_loads([I|Is], L, Index) -> + [I|opt_useless_block_loads(Is, L, Index)]; +opt_useless_block_loads([], _L, _Index) -> + []. + maps_append_list(K,Vs,M) -> case M of #{K:=Vs0} -> M#{K:=Vs0++Vs}; % same order as dict |