diff options
Diffstat (limited to 'lib/compiler/src/beam_dead.erl')
| -rw-r--r-- | lib/compiler/src/beam_dead.erl | 676 |
1 files changed, 462 insertions, 214 deletions
diff --git a/lib/compiler/src/beam_dead.erl b/lib/compiler/src/beam_dead.erl index b15adfa889..7cd07dc3be 100644 --- a/lib/compiler/src/beam_dead.erl +++ b/lib/compiler/src/beam_dead.erl @@ -21,112 +21,10 @@ -export([module/2]). -%%% The following optimisations are done: -%%% -%%% (1) In this code -%%% -%%% move DeadValue {x,0} -%%% jump L2 -%%% . -%%% . -%%% . -%%% L2: move Anything {x,0} -%%% . -%%% . -%%% . -%%% -%%% the first assignment to {x,0} has no effect (is dead), -%%% so it can be removed. Besides removing a move instruction, -%%% if the move was preceeded by a label, the resulting code -%%% will look this -%%% -%%% L1: jump L2 -%%% . -%%% . -%%% . -%%% L2: move Anything {x,0} -%%% . -%%% . -%%% . -%%% -%%% which can be further optimized by the jump optimizer (beam_jump). -%%% -%%% (2) In this code -%%% -%%% L1: move AtomLiteral {x,0} -%%% jump L2 -%%% . -%%% . -%%% . -%%% L2: test is_atom FailLabel {x,0} -%%% select_val {x,0}, FailLabel [... AtomLiteral => L3...] -%%% . -%%% . -%%% . -%%% L3: ... -%%% -%%% FailLabel: ... -%%% -%%% the first code fragment can be changed to -%%% -%%% L1: move AtomLiteral {x,0} -%%% jump L3 -%%% -%%% If the literal is not included in the table of literals in the -%%% select_val instruction, the first code fragment will instead be -%%% rewritten as: -%%% -%%% L1: move AtomLiteral {x,0} -%%% jump FailLabel -%%% -%%% The move instruction will be removed by optimization (1) above, -%%% if the code following the L3 label overwrites {x,0}. -%%% -%%% The code following the L2 label will be kept, but it will be removed later -%%% by the jump optimizer. -%%% -%%% (3) In this code -%%% -%%% test is_eq_exact ALabel Src Dst -%%% move Src Dst -%%% -%%% the move instruction can be removed. -%%% Same thing for -%%% -%%% test is_nil ALabel Dst -%%% move [] Dst -%%% -%%% -%%% (4) In this code -%%% -%%% select_val {x,Reg}, ALabel [... Literal => L1...] -%%% . -%%% . -%%% . -%%% L1: move Literal {x,Reg} -%%% -%%% we can remove the move instruction. -%%% -%%% (5) In the following code -%%% -%%% bif '=:=' Fail Src1 Src2 {x,0} -%%% jump L1 -%%% . -%%% . -%%% . -%%% L1: select_val {x,0}, ALabel [... true => L2..., ...false => L3...] -%%% . -%%% . -%%% . -%%% L2: .... L3: .... -%%% -%%% the first two instructions can be replaced with -%%% -%%% test is_eq_exact L3 Src1 Src2 -%%% jump L2 -%%% -%%% provided that {x,0} is killed at both L2 and L3. -%%% +%%% Dead code is code that is executed but has no effect. This +%%% optimization pass either removes dead code or jumps around it, +%%% potentially making it unreachable and a target for the +%%% the beam_jump pass. -import(lists, [mapfoldl/3,reverse/1]). @@ -173,7 +71,28 @@ move_move_into_block([I|Is], Acc) -> move_move_into_block([], Acc) -> reverse(Acc). %%% -%%% Scan instructions in execution order and remove dead code. +%%% Scan instructions in execution order and remove redundant 'move' +%%% instructions. 'move' instructions are redundant if we know that +%%% the register already contains the value being assigned, as in the +%%% following code: +%%% +%%% test is_eq_exact SomeLabel Src Dst +%%% move Src Dst +%%% +%%% or in: +%%% +%%% test is_nil SomeLabel Dst +%%% move nil Dst +%%% +%%% or in: +%%% +%%% select_val Register FailLabel [... Literal => L1...] +%%% . +%%% . +%%% . +%%% L1: move Literal Register +%%% +%%% Also add extra labels to help the second backward pass. %%% forward(Is, Lc) -> @@ -215,15 +134,13 @@ forward([{test,is_eq_exact,_,[Dst,Src]}=I,{move,Src,Dst}|Is], D, Lc, Acc) -> forward([I|Is], D, Lc, Acc); forward([{test,is_nil,_,[Dst]}=I,{move,nil,Dst}|Is], D, Lc, Acc) -> forward([I|Is], D, Lc, Acc); -forward([{test,is_eq_exact,_,_}=I|Is], D, Lc, Acc) -> - case Is of - [{label,_}|_] -> forward(Is, D, Lc, [I|Acc]); - _ -> forward(Is, D, Lc+1, [{label,Lc},I|Acc]) - end; -forward([{test,is_ne_exact,_,_}=I|Is], D, Lc, Acc) -> - case Is of - [{label,_}|_] -> forward(Is, D, Lc, [I|Acc]); - _ -> forward(Is, D, Lc+1, [{label,Lc},I|Acc]) +forward([{test,_,_,_}=I|Is]=Is0, D, 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. + 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(Is, D, Lc, [I|Acc]); @@ -239,9 +156,49 @@ update_value_dict([Lit,{f,Lbl}|T], Reg, D0) -> update_value_dict(T, Reg, D); update_value_dict([], _, D) -> D. +useful_to_insert_label([_,{label,_}|_]) -> + false; +useful_to_insert_label([{test,Op,_,_}|_]) -> + case Op of + is_lt -> true; + is_ge -> true; + is_eq_exact -> true; + is_ne_exact -> true; + _ -> false + end. + +%%% +%%% Scan instructions in reverse execution order and try to +%%% shortcut branch instructions. +%%% +%%% For example, in this code: +%%% +%%% move Literal Register +%%% jump L1 +%%% . +%%% . +%%% . +%%% L1: test is_{integer,atom} FailLabel Register +%%% select_val {x,0} FailLabel [... Literal => L2...] +%%% . +%%% . +%%% . +%%% L2: ... %%% -%%% Scan instructions in reverse execution order and remove dead code. +%%% the 'selectval' instruction will always transfer control to L2, +%%% so we can just as well jump to L2 directly by rewriting the +%%% first part of the sequence like this: %%% +%%% move Literal Register +%%% jump L2 +%%% +%%% If register Register is killed at label L2, we can remove the +%%% 'move' instruction, leaving just the 'jump' instruction: +%%% +%%% jump L2 +%%% +%%% These transformations may leave parts of the code unreachable. +%%% The beam_jump pass will remove the unreachable code. backward(Is, D) -> backward(Is, D, []). @@ -277,15 +234,10 @@ backward([{select,select_val,Reg,{f,Fail0},List0}|Is], D, Acc) -> Fail = shortcut_bs_test(Fail1, Is, D), Sel = {select,select_val,Reg,{f,Fail},List}, backward(Is, D, [Sel|Acc]); -backward([{jump,{f,To0}},{move,Src,Reg}=Move0|Is], D, Acc) -> - {To,Move} = case Src of - {atom,Val0} -> - To1 = shortcut_select_label(To0, Reg, Val0, D), - {To2,Val} = shortcut_boolean_label(To1, Reg, Val0, D), - {To2,{move,{atom,Val},Reg}}; - _ -> - {shortcut_label(To0, D),Move0} - end, +backward([{jump,{f,To0}},{move,Src0,Reg}|Is], D, Acc) -> + To1 = shortcut_select_label(To0, Reg, Src0, D), + {To,Src} = shortcut_boolean_label(To1, Reg, Src0, D), + Move = {move,Src,Reg}, Jump = {jump,{f,To}}, case beam_utils:is_killed_at(Reg, To, D) of false -> backward([Move|Is], D, [Jump|Acc]); @@ -301,28 +253,25 @@ backward([{test,bs_start_match2,{f,To0},Live,[Src|_]=Info,Dst}|Is], D, Acc) -> To = shortcut_bs_start_match(To0, Src, D), I = {test,bs_start_match2,{f,To},Live,Info,Dst}, backward(Is, D, [I|Acc]); -backward([{test,is_eq_exact,{f,To0},[Reg,{atom,Val}]=Ops}|Is], D, Acc) -> - To1 = shortcut_bs_test(To0, Is, D), - To = shortcut_fail_label(To1, Reg, Val, D), - I = combine_eqs(To, Ops, D, Acc), - backward(Is, D, [I|Acc]); backward([{test,Op,{f,To0},Ops0}|Is], D, Acc) -> To1 = shortcut_bs_test(To0, Is, D), To2 = shortcut_label(To1, D), + To3 = shortcut_rel_op(To2, Op, Ops0, D), + %% Try to shortcut a repeated test: %% %% test Op {f,Fail1} Operands test Op {f,Fail2} Operands %% . . . ==> ... %% Fail1: test Op {f,Fail2} Operands Fail1: test Op {f,Fail2} Operands %% - To = case beam_utils:code_at(To2, D) of - [{test,Op,{f,To3},Ops}|_] -> + To = case beam_utils:code_at(To3, D) of + [{test,Op,{f,To4},Ops}|_] -> case equal_ops(Ops0, Ops) of - true -> To3; - false -> To2 + true -> To4; + false -> To3 end; _Code -> - To2 + To3 end, I = case Op of is_eq_exact -> combine_eqs(To, Ops0, D, Acc); @@ -367,8 +316,8 @@ equal_ops([Op|T0], [Op|T1]) -> equal_ops([], []) -> true; equal_ops(_, _) -> false. -shortcut_select_list([{_,Val}=Lit,{f,To0}|T], Reg, D, Acc) -> - To = shortcut_select_label(To0, Reg, Val, D), +shortcut_select_list([Lit,{f,To0}|T], Reg, D, Acc) -> + To = shortcut_select_label(To0, Reg, Lit, D), shortcut_select_list(T, Reg, D, [{f,To},Lit|Acc]); shortcut_select_list([], _, _, Acc) -> reverse(Acc). @@ -378,58 +327,39 @@ shortcut_label(To0, D) -> _ -> To0 end. -shortcut_select_label(To0, Reg, Val, D) -> - case beam_utils:code_at(To0, D) of - [{jump,{f,To}}|_] -> - shortcut_select_label(To, Reg, Val, D); - [{test,is_atom,_,[Reg]},{select,select_val,Reg,{f,Fail},Map}|_] -> - To = find_select_val(Map, Val, Fail), - shortcut_select_label(To, Reg, Val, D); - [{test,is_eq_exact,{f,_},[Reg,{atom,Val}]},{label,To}|_] when is_atom(Val) -> - shortcut_select_label(To, Reg, Val, D); - [{test,is_eq_exact,{f,_},[Reg,{atom,Val}]},{jump,{f,To}}|_] when is_atom(Val) -> - shortcut_select_label(To, Reg, Val, D); - [{test,is_eq_exact,{f,To},[Reg,{atom,AnotherVal}]}|_] - when is_atom(Val), Val =/= AnotherVal -> - shortcut_select_label(To, Reg, Val, D); - [{test,is_ne_exact,{f,To},[Reg,{atom,Val}]}|_] when is_atom(Val) -> - shortcut_select_label(To, Reg, Val, D); - [{test,is_ne_exact,{f,_},[Reg,{atom,_}]},{label,To}|_] when is_atom(Val) -> - shortcut_select_label(To, Reg, Val, D); - [{test,is_tuple,{f,To},[Reg]}|_] when is_atom(Val) -> - shortcut_select_label(To, Reg, Val, D); - _ -> - To0 - end. +shortcut_select_label(To, Reg, Lit, D) -> + shortcut_rel_op(To, is_ne_exact, [Reg,Lit], D). -shortcut_fail_label(To0, Reg, Val, D) -> - case beam_utils:code_at(To0, D) of - [{jump,{f,To}}|_] -> - shortcut_fail_label(To, Reg, Val, D); - [{test,is_eq_exact,{f,To},[Reg,{atom,Val}]}|_] when is_atom(Val) -> - shortcut_fail_label(To, Reg, Val, D); - _ -> - To0 - end. - -shortcut_boolean_label(To0, Reg, Bool0, D) when is_boolean(Bool0) -> +shortcut_boolean_label(To0, Reg, {atom,Bool0}=Lit, D) when is_boolean(Bool0) -> case beam_utils:code_at(To0, D) of [{line,_},{bif,'not',_,[Reg],Reg},{jump,{f,To}}|_] -> - Bool = not Bool0, + Bool = {atom,not Bool0}, {shortcut_select_label(To, Reg, Bool, D),Bool}; _ -> - {To0,Bool0} + {To0,Lit} end; shortcut_boolean_label(To, _, Bool, _) -> {To,Bool}. -find_select_val([{_,Val},{f,To}|_], Val, _) -> To; -find_select_val([{_,_}, {f,_}|T], Val, Fail) -> - find_select_val(T, Val, Fail); -find_select_val([], _, Fail) -> Fail. +%% Replace a comparison operator with a test instruction and a jump. +%% For example, if we have this code: +%% +%% bif '=:=' Fail Src1 Src2 {x,0} +%% jump L1 +%% . +%% . +%% . +%% L1: select_val {x,0} FailLabel [... true => L2..., ...false => L3...] +%% +%% the first two instructions can be replaced with +%% +%% test is_eq_exact L3 Src1 Src2 +%% jump L2 +%% +%% provided that {x,0} is killed at both L2 and L3. replace_comp_op(To, Reg, Op, Ops, D) -> - False = comp_op_find_shortcut(To, Reg, false, D), - True = comp_op_find_shortcut(To, Reg, true, D), + False = comp_op_find_shortcut(To, Reg, {atom,false}, D), + True = comp_op_find_shortcut(To, Reg, {atom,true}, D), [bif_to_test(Op, Ops, False),{jump,{f,True}}]. comp_op_find_shortcut(To0, Reg, Val, D) -> @@ -461,9 +391,9 @@ not_possible() -> throw(not_possible). %% %% is_eq_exact F1 Reg Lit1 select_val Reg F2 [ Lit1 L1 %% L1: . Lit2 L2 ] -%% . -%% . ==> -%% . +%% . +%% . ==> +%% . %% F1: is_eq_exact F2 Reg Lit2 F1: is_eq_exact F2 Reg Lit2 %% L2: .... L2: %% @@ -488,31 +418,26 @@ remove_from_list(Lit, [Val,{f,_}=Fail|T]) -> [Val,Fail|remove_from_list(Lit, T)]; remove_from_list(_, []) -> []. -%% shortcut_bs_test(TargetLabel, [Instruction], D) -> TargetLabel' -%% Try to shortcut the failure label for a bit syntax matching. -%% We know that the binary contains at least Bits bits after -%% the latest save point. +%% shortcut_bs_test(TargetLabel, ReversedInstructions, D) -> TargetLabel' +%% Try to shortcut the failure label for bit syntax matching. shortcut_bs_test(To, Is, D) -> shortcut_bs_test_1(beam_utils:code_at(To, D), Is, To, D). -shortcut_bs_test_1([{bs_restore2,Reg,SavePoint}|Is], PrevIs, To, D) -> - shortcut_bs_test_2(Is, {Reg,SavePoint}, PrevIs, To, D); -shortcut_bs_test_1([_|_], _, To, _) -> To. - -shortcut_bs_test_2([{label,_}|Is], Save, PrevIs, To, D) -> - shortcut_bs_test_2(Is, Save, PrevIs, To, D); -shortcut_bs_test_2([{test,bs_test_tail2,{f,To},[_,TailBits]}|_], - {Reg,_Point} = RP, PrevIs, To0, D) -> - case count_bits_matched(PrevIs, RP, 0) of +shortcut_bs_test_1([{bs_restore2,Reg,SavePoint}, + {label,_}, + {test,bs_test_tail2,{f,To},[_,TailBits]}|_], + PrevIs, To0, D) -> + case count_bits_matched(PrevIs, {Reg,SavePoint}, 0) of Bits when Bits > TailBits -> %% This instruction will fail. We know because a restore has been - %% done from the previous point SavePoint in the binary, and we also know - %% that the binary contains at least Bits bits from SavePoint. + %% done from the previous point SavePoint in the binary, and we + %% also know that the binary contains at least Bits bits from + %% SavePoint. %% %% Since we will skip a bs_restore2 if we shortcut to label To, - %% we must now make sure that code at To does not depend on the position - %% in the context in any way. + %% we must now make sure that code at To does not depend on + %% the position in the context in any way. case shortcut_bs_pos_used(To, Reg, D) of false -> To; true -> To0 @@ -520,8 +445,19 @@ shortcut_bs_test_2([{test,bs_test_tail2,{f,To},[_,TailBits]}|_], _Bits -> To0 end; -shortcut_bs_test_2([_|_], _, _, To, _) -> To. +shortcut_bs_test_1([_|_], _, To, _) -> To. +%% counts_bits_matched(ReversedInstructions, SavePoint, Bits) -> Bits' +%% Given a reversed instruction stream, determine the minimum number +%% of bits that will be matched by bit syntax instructions up to the +%% given save point. + +count_bits_matched([{test,bs_get_utf8,{f,_},_,_,_}|Is], SavePoint, Bits) -> + count_bits_matched(Is, SavePoint, Bits+8); +count_bits_matched([{test,bs_get_utf16,{f,_},_,_,_}|Is], SavePoint, Bits) -> + count_bits_matched(Is, SavePoint, Bits+16); +count_bits_matched([{test,bs_get_utf32,{f,_},_,_,_}|Is], SavePoint, Bits) -> + count_bits_matched(Is, SavePoint, Bits+32); count_bits_matched([{test,_,_,_,[_,Sz,U,{field_flags,_}],_}|Is], SavePoint, Bits) -> case Sz of {integer,N} -> count_bits_matched(Is, SavePoint, Bits+N*U); @@ -545,20 +481,332 @@ shortcut_bs_pos_used_1(Is, Reg, D) -> not beam_utils:is_killed(Reg, Is, D). %% shortcut_bs_start_match(TargetLabel, Reg) -> TargetLabel -%% A failing bs_start_match2 instruction means that the source -%% cannot be a binary, so there is no need to jump bs_context_to_binary/1 -%% or another bs_start_match2 instruction. +%% A failing bs_start_match2 instruction means that the source (Reg) +%% cannot be a binary. That means that it is safe to skip +%% bs_context_to_binary instructions operating on Reg, and +%% bs_start_match2 instructions operating on Reg. shortcut_bs_start_match(To, Reg, D) -> - shortcut_bs_start_match_1(beam_utils:code_at(To, D), Reg, To). + shortcut_bs_start_match_1(beam_utils:code_at(To, D), Reg, To, D). + +shortcut_bs_start_match_1([{bs_context_to_binary,Reg}|Is], Reg, To, D) -> + shortcut_bs_start_match_1(Is, Reg, To, D); +shortcut_bs_start_match_1([{jump,{f,To}}|_], Reg, _, D) -> + Code = beam_utils:code_at(To, D), + shortcut_bs_start_match_1(Code, Reg, To, D); +shortcut_bs_start_match_1([{test,bs_start_match2,{f,To},_,[Reg|_],_}|_], + Reg, _, D) -> + Code = beam_utils:code_at(To, D), + shortcut_bs_start_match_1(Code, Reg, To, D); +shortcut_bs_start_match_1(_, _, To, _) -> + To. -shortcut_bs_start_match_1([{bs_context_to_binary,Reg}|Is], Reg, To) -> - shortcut_bs_start_match_2(Is, Reg, To); -shortcut_bs_start_match_1(_, _, To) -> To. +%% shortcut_rel_op(FailLabel, Operator, [Operand], D) -> FailLabel' +%% Try to shortcut the given test instruction. Example: +%% +%% is_ge L1 {x,0} 48 +%% . +%% . +%% . +%% L1: is_ge L2 {x,0} 65 +%% +%% The first test instruction can be rewritten to "is_ge L2 {x,0} 48" +%% since the instruction at L1 will also fail. +%% +%% If there are instructions between L1 and the other test instruction +%% it may still be possible to do the shortcut. For example: +%% +%% L1: is_eq_exact L3 {x,0} 92 +%% is_ge L2 {x,0} 65 +%% +%% Since the first test instruction failed, we know that {x,0} must +%% be less than 48; therefore, we know that {x,0} cannot be equal to +%% 92 and the jump to L3 cannot happen. + +shortcut_rel_op(To, Op, Ops, D) -> + case normalize_op({test,Op,{f,To},Ops}) of + {{NormOp,A,B},_} -> + Normalized = {negate_op(NormOp),A,B}, + shortcut_rel_op_fp(To, Normalized, D); + {_,_} -> + To; + error -> + To + end. -shortcut_bs_start_match_2([{jump,{f,To}}|_], _, _) -> - To; -shortcut_bs_start_match_2([{test,bs_start_match2,{f,To},_,[Reg|_],_}|_], Reg, _) -> - To; -shortcut_bs_start_match_2(_Is, _Reg, To) -> - To. +shortcut_rel_op_fp(To0, Normalized, D) -> + Code = beam_utils:code_at(To0, D), + case shortcut_any_label(Code, Normalized) of + error -> + To0; + To -> + shortcut_rel_op_fp(To, Normalized, D) + end. + +%% shortcut_any_label([Instruction], PrevCondition) -> FailLabel | error +%% Using PrevCondition (a previous condition known to be true), +%% try to shortcut to another failure label. + +shortcut_any_label([{jump,{f,Lbl}}|_], _Prev) -> + Lbl; +shortcut_any_label([{label,Lbl}|_], _Prev) -> + Lbl; +shortcut_any_label([{select,select_val,R,{f,Fail},L}|_], Prev) -> + shortcut_selectval(L, R, Fail, Prev); +shortcut_any_label([I|Is], Prev) -> + case normalize_op(I) of + error -> + error; + {Normalized,Fail} -> + %% We have a relational operator. + case will_succeed(Prev, Normalized) of + no -> + %% This test instruction will always branch + %% to Fail. + Fail; + yes -> + %% This test instruction will never branch, + %% so we will look at the next instruction. + shortcut_any_label(Is, Prev); + maybe -> + %% May or may not branch. From now on, we can only + %% shortcut to the this specific failure label + %% Fail. + shortcut_specific_label(Is, Fail, Prev) + end + end. + +%% shortcut_specific_label([Instruction], FailLabel, PrevCondition) -> +%% FailLabel | error +%% We have previously encountered a test instruction that may or +%% may not branch to FailLabel. Therefore we are only allowed +%% to do the shortcut to the same fail label (FailLabel). + +shortcut_specific_label([{label,_}|Is], Fail, Prev) -> + shortcut_specific_label(Is, Fail, Prev); +shortcut_specific_label([{select,select_val,R,{f,F},L}|_], Fail, Prev) -> + case shortcut_selectval(L, R, F, Prev) of + Fail -> Fail; + _ -> error + end; +shortcut_specific_label([I|Is], Fail, Prev) -> + case normalize_op(I) of + error -> + error; + {Normalized,Fail} -> + case will_succeed(Prev, Normalized) of + no -> + %% Will branch to FailLabel. + Fail; + yes -> + %% Will definitely never branch. + shortcut_specific_label(Is, Fail, Prev); + maybe -> + %% May branch, but still OK since it will branch + %% to FailLabel. + shortcut_specific_label(Is, Fail, Prev) + end; + {Normalized,_} -> + %% This test instruction will branch to a different + %% fail label, if it branches at all. + case will_succeed(Prev, Normalized) of + yes -> + %% Still OK, since the branch will never be + %% taken. + shortcut_specific_label(Is, Fail, Prev); + no -> + %% Give up. The branch will definitely be taken + %% to a different fail label. + error; + maybe -> + %% Give up. If the branch is taken, it will be + %% to a different fail label. + error + end + end. + + +%% shortcut_selectval(List, Reg, Fail, PrevCond) -> FailLabel | error +%% Try to shortcut a selectval instruction. A selectval instruction +%% is equivalent to the following instruction sequence: +%% +%% is_ne_exact L1 Reg Value1 +%% . +%% . +%% . +%% is_ne_exact LN Reg ValueN +%% jump DefaultFailLabel +%% +shortcut_selectval([Val,{f,Lbl}|T], R, Fail, Prev) -> + case will_succeed(Prev, {'=/=',R,get_literal(Val)}) of + yes -> shortcut_selectval(T, R, Fail, Prev); + no -> Lbl; + maybe -> error + end; +shortcut_selectval([], _, Fail, _) -> Fail. + +%% will_succeed(PrevCondition, Condition) -> yes | no | maybe +%% PrevCondition is a condition known to be true. This function +%% will tell whether Condition will succeed. + +will_succeed({Op1,Reg,A}, {Op2,Reg,B}) -> + will_succeed_1(Op1, A, Op2, B); +will_succeed({'=:=',Reg,{literal,A}}, {TypeTest,Reg}) -> + case erlang:TypeTest(A) of + false -> no; + true -> yes + end; +will_succeed({_,_,_}, maybe) -> + maybe; +will_succeed({_,_,_}, Test) when is_tuple(Test) -> + maybe. + +will_succeed_1('=:=', A, '<', B) -> + if + B =< A -> no; + true -> yes + end; +will_succeed_1('=:=', A, '=<', B) -> + if + B < A -> no; + true -> yes + end; +will_succeed_1('=:=', A, '=:=', B) -> + if + A =:= B -> yes; + true -> no + end; +will_succeed_1('=:=', A, '=/=', B) -> + if + A =:= B -> no; + true -> yes + end; +will_succeed_1('=:=', A, '>=', B) -> + if + B > A -> no; + true -> yes + end; +will_succeed_1('=:=', A, '>', B) -> + if + B >= A -> no; + true -> yes + end; + +will_succeed_1('=/=', A, '=/=', B) when A =:= B -> yes; +will_succeed_1('=/=', A, '=:=', B) when A =:= B -> no; + +will_succeed_1('<', A, '=:=', B) when B >= A -> no; +will_succeed_1('<', A, '=/=', B) when B >= A -> yes; +will_succeed_1('<', A, '<', B) when B >= A -> yes; +will_succeed_1('<', A, '=<', B) when B > A -> yes; +will_succeed_1('<', A, '>=', B) when B > A -> no; +will_succeed_1('<', A, '>', B) when B >= A -> no; + +will_succeed_1('=<', A, '=:=', B) when B > A -> no; +will_succeed_1('=<', A, '=/=', B) when B > A -> yes; +will_succeed_1('=<', A, '<', B) when B > A -> yes; +will_succeed_1('=<', A, '=<', B) when B >= A -> yes; +will_succeed_1('=<', A, '>=', B) when B > A -> no; +will_succeed_1('=<', A, '>', B) when B >= A -> no; + +will_succeed_1('>=', A, '=:=', B) when B < A -> no; +will_succeed_1('>=', A, '=/=', B) when B < A -> yes; +will_succeed_1('>=', A, '<', B) when B =< A -> no; +will_succeed_1('>=', A, '=<', B) when B < A -> no; +will_succeed_1('>=', A, '>=', B) when B =< A -> yes; +will_succeed_1('>=', A, '>', B) when B < A -> yes; + +will_succeed_1('>', A, '=:=', B) when B =< A -> no; +will_succeed_1('>', A, '=/=', B) when B =< A -> yes; +will_succeed_1('>', A, '<', B) when B =< A -> no; +will_succeed_1('>', A, '=<', B) when B < A -> no; +will_succeed_1('>', A, '>=', B) when B =< A -> yes; +will_succeed_1('>', A, '>', B) when B < A -> yes; + +will_succeed_1(_, _, _, _) -> maybe. + +%% normalize_op(Instruction) -> {Normalized,FailLabel} | error +%% Normalized = {Operator,Register,Literal} | +%% {TypeTest,Register} | +%% maybe +%% Operation = '<' | '=<' | '=:=' | '=/=' | '>=' | '>' +%% TypeTest = is_atom | is_integer ... +%% Literal = {literal,Term} +%% +%% Normalize a relational operator to facilitate further +%% comparisons between operators. Always make the register +%% operand the first operand. Thus the following instruction: +%% +%% {test,is_ge,{f,99},{integer,13},{x,0}} +%% +%% will be normalized to: +%% +%% {'=<',{x,0},{literal,13}} +%% +%% NOTE: Bit syntax test instructions are scary. They may change the +%% state of match contexts and update registers, so we don't dare +%% mess with them. + +normalize_op({test,is_ge,{f,Fail},Ops}) -> + normalize_op_1('>=', Ops, Fail); +normalize_op({test,is_lt,{f,Fail},Ops}) -> + normalize_op_1('<', Ops, Fail); +normalize_op({test,is_eq_exact,{f,Fail},Ops}) -> + normalize_op_1('=:=', Ops, Fail); +normalize_op({test,is_ne_exact,{f,Fail},Ops}) -> + normalize_op_1('=/=', Ops, Fail); +normalize_op({test,is_nil,{f,Fail},[R]}) -> + normalize_op_1('=:=', [R,nil], Fail); +normalize_op({test,Op,{f,Fail},[R]}) -> + case erl_internal:new_type_test(Op, 1) of + true -> {{Op,R},Fail}; + false -> {maybe,Fail} + end; +normalize_op({test,_,{f,Fail},_}=I) -> + case beam_utils:is_pure_test(I) of + true -> {maybe,Fail}; + false -> error + end; +normalize_op(_) -> + error. + +normalize_op_1(Op, [Op1,Op2], Fail) -> + case {get_literal(Op1),get_literal(Op2)} of + {error,error} -> + %% Both operands are registers. + {maybe,Fail}; + {error,Lit} -> + {{Op,Op1,Lit},Fail}; + {Lit,error} -> + {{turn_op(Op),Op2,Lit},Fail}; + {_,_} -> + %% Both operands are literals. Can probably only + %% happen if the Core Erlang optimizations passes were + %% turned off, so don't bother trying to do something + %% smart here. + {maybe,Fail} + end. + +turn_op('<') -> '>'; +turn_op('>=') -> '=<'; +turn_op('=:='=Op) -> Op; +turn_op('=/='=Op) -> Op. + +negate_op('>=') -> '<'; +negate_op('<') -> '>='; +negate_op('=<') -> '>'; +negate_op('>') -> '=<'; +negate_op('=:=') -> '=/='; +negate_op('=/=') -> '=:='. + +get_literal({atom,Val}) -> + {literal,Val}; +get_literal({integer,Val}) -> + {literal,Val}; +get_literal({float,Val}) -> + {literal,Val}; +get_literal(nil) -> + {literal,[]}; +get_literal({literal,_}=Lit) -> + Lit; +get_literal({_,_}) -> error. |