diff options
Diffstat (limited to 'lib/compiler/src/beam_dead.erl')
| -rw-r--r-- | lib/compiler/src/beam_dead.erl | 55 |
1 files changed, 51 insertions, 4 deletions
diff --git a/lib/compiler/src/beam_dead.erl b/lib/compiler/src/beam_dead.erl index 6f6d742293..9087586b58 100644 --- a/lib/compiler/src/beam_dead.erl +++ b/lib/compiler/src/beam_dead.erl @@ -266,20 +266,42 @@ backward([{jump,{f,To0}},{move,Src,Reg}=Move|Is], D, Acc) -> false -> backward([Move|Is], D, [Jump|Acc]); true -> backward([Jump|Is], D, Acc) end; -backward([{jump,{f,To}}=J|[{bif,Op,_,Ops,Reg}|Is]=Is0], D, Acc) -> +backward([{jump,{f,To}}=J|[{bif,Op,{f,BifFail},Ops,Reg}|Is]=Is0], D, Acc) -> try replace_comp_op(To, Reg, Op, Ops, D) of I -> backward(Is, D, I++Acc) catch - throw:not_possible -> backward(Is0, D, [J|Acc]) + throw:not_possible -> + case To =:= BifFail of + true -> + %% The bif instruction is redundant. See the comment + %% in the next clause for why there is no need to + %% test for liveness of Reg at label To. + backward([J|Is], D, Acc); + false -> + backward(Is0, D, [J|Acc]) + end end; -backward([{test,bs_start_match2,F,_,[R,_],Ctxt}=I|Is], D, +backward([{jump,{f,To}}=J|[{gc_bif,_,{f,To},_,_,_Dst}|Is]], D, Acc) -> + %% The gc_bif instruction is redundant, since either the gc_bif + %% instruction itself or the jump instruction will transfer control + %% to label To. Note that a gc_bif instruction does not assign its + %% destination register if the failure branch is taken; therefore, + %% the code at label To is not allowed to assume that the destination + %% register is initialized, and it is therefore no need to test + %% for liveness of the destination register at label To. + backward([J|Is], D, Acc); +backward([{test,bs_start_match2,F,Live,[R,_]=Args,Ctxt}|Is], D, [{test,bs_match_string,F,[Ctxt,Bs]}, {test,bs_test_tail2,F,[Ctxt,0]}|Acc0]=Acc) -> + {f,To0} = F, case beam_utils:is_killed(Ctxt, Acc0, D) of true -> - Eq = {test,is_eq_exact,F,[R,{literal,Bs}]}, + To = shortcut_bs_context_to_binary(To0, R, D), + Eq = {test,is_eq_exact,{f,To},[R,{literal,Bs}]}, backward(Is, D, [Eq|Acc0]); false -> + To = shortcut_bs_start_match(To0, R, D), + I = {test,bs_start_match2,{f,To},Live,Args,Ctxt}, backward(Is, D, [I|Acc]) end; backward([{test,bs_start_match2,{f,To0},Live,[Src|_]=Info,Dst}|Is], D, Acc) -> @@ -357,6 +379,14 @@ backward([{kill,_}=I|Is], D, [{line,_},Exit|_]=Acc) -> false -> backward(Is, D, [I|Acc]); true -> backward(Is, D, Acc) end; +backward([{bif,'or',{f,To0},[Dst,{atom,false}],Dst}=I|Is], D, + [{test,is_eq_exact,{f,To},[Dst,{atom,true}]}|_]=Acc) -> + case shortcut_label(To0, D) of + To -> + backward(Is, D, Acc); + _ -> + backward(Is, D, [I|Acc]) + end; backward([I|Is], D, Acc) -> backward(Is, D, [I|Acc]); backward([], _D, Acc) -> Acc. @@ -375,6 +405,8 @@ shortcut_select_list([Lit,{f,To0}|T], Reg, D, Acc) -> shortcut_select_list(T, Reg, D, [{f,To},Lit|Acc]); shortcut_select_list([], _, _, Acc) -> reverse(Acc). +shortcut_label(0, _) -> + 0; shortcut_label(To0, D) -> case beam_utils:code_at(To0, D) of [{jump,{f,To}}|_] -> shortcut_label(To, D); @@ -551,6 +583,21 @@ shortcut_bs_start_match_1([{test,bs_start_match2,{f,To},_,[Reg|_],_}|_], shortcut_bs_start_match_1(_, _, To, _) -> To. +%% shortcut_bs_context_to_binary(TargetLabel, Reg) -> TargetLabel +%% If a bs_start_match2 instruction has been eliminated, the +%% bs_context_to_binary instruction can be eliminated too. + +shortcut_bs_context_to_binary(To, Reg, D) -> + shortcut_bs_ctb_1(beam_utils:code_at(To, D), Reg, To, D). + +shortcut_bs_ctb_1([{bs_context_to_binary,Reg}|Is], Reg, To, D) -> + shortcut_bs_ctb_1(Is, Reg, To, D); +shortcut_bs_ctb_1([{jump,{f,To}}|_], Reg, _, D) -> + Code = beam_utils:code_at(To, D), + shortcut_bs_ctb_1(Code, Reg, To, D); +shortcut_bs_ctb_1(_, _, To, _) -> + To. + %% shortcut_rel_op(FailLabel, Operator, [Operand], D) -> FailLabel' %% Try to shortcut the given test instruction. Example: %% |