diff options
Diffstat (limited to 'lib/compiler/src/beam_block.erl')
| -rw-r--r-- | lib/compiler/src/beam_block.erl | 604 |
1 files changed, 15 insertions, 589 deletions
diff --git a/lib/compiler/src/beam_block.erl b/lib/compiler/src/beam_block.erl index fe43163455..9d8d5b2b0c 100644 --- a/lib/compiler/src/beam_block.erl +++ b/lib/compiler/src/beam_block.erl @@ -17,39 +17,24 @@ %% %% %CopyrightEnd% %% -%% Purpose : Partitions assembly instructions into basic blocks and -%% optimizes them. +%% Purpose: Partition BEAM instructions into basic blocks. -module(beam_block). -export([module/2]). --import(lists, [reverse/1,reverse/2,member/2]). +-import(lists, [reverse/1,splitwith/2]). -spec module(beam_utils:module_code(), [compile:option()]) -> {'ok',beam_utils:module_code()}. -module({Mod,Exp,Attr,Fs0,Lc}, Opts) -> - Blockify = not member(no_blockify, Opts), - Fs = [function(F, Blockify) || F <- Fs0], +module({Mod,Exp,Attr,Fs0,Lc}, _Opts) -> + Fs = [function(F) || F <- Fs0], {ok,{Mod,Exp,Attr,Fs,Lc}}. -function({function,Name,Arity,CLabel,Is0}, Blockify) -> +function({function,Name,Arity,CLabel,Is0}) -> try - %% Collect basic blocks and optimize them. - Is1 = case Blockify of - false -> Is0; - true -> blockify(Is0) - end, - Is2 = embed_lines(Is1), - Is3 = local_cse(Is2), - Is4 = beam_utils:anno_defs(Is3), - Is5 = move_allocates(Is4), - Is6 = beam_utils:live_opt(Is5), - Is7 = opt_blocks(Is6), - Is8 = beam_utils:delete_annos(Is7), - Is = opt_allocs(Is8), - - %% Done. + Is1 = blockify(Is0), + Is = embed_lines(Is1), {function,Name,Arity,CLabel,Is} catch Class:Error:Stack -> @@ -64,9 +49,6 @@ function({function,Name,Arity,CLabel,Is0}, Blockify) -> blockify(Is) -> blockify(Is, []). -blockify([{loop_rec,{f,Fail},{x,0}},{loop_rec_end,_Lbl},{label,Fail}|Is], Acc) -> - %% Useless instruction sequence. - blockify(Is, Acc); blockify([I|Is0]=IsAll, Acc) -> case collect(I) of error -> blockify(Is0, [I|Acc]); @@ -80,12 +62,10 @@ collect_block(Is) -> collect_block(Is, []). collect_block([{allocate,N,R}|Is0], Acc) -> - {Inits,Is} = lists:splitwith(fun ({init,{y,_}}) -> true; - (_) -> false - end, Is0), + {Inits,Is} = splitwith(fun ({init,{y,_}}) -> true; + (_) -> false + end, Is0), collect_block(Is, [{set,[],[],{alloc,R,{nozero,N,0,Inits}}}|Acc]); -collect_block([{allocate_zero,Ns,R},{test_heap,Nh,R}|Is], Acc) -> - collect_block(Is, [{set,[],[],{alloc,R,{zero,Ns,Nh,[]}}}|Acc]); collect_block([I|Is]=Is0, Acc) -> case collect(I) of error -> {reverse(Acc),Is0}; @@ -100,23 +80,20 @@ collect({allocate_heap,Ns,Nh,R}) -> {set,[],[],{alloc,R,{nozero,Ns,Nh,[]}}}; collect({allocate_heap_zero,Ns,Nh,R}) -> {set,[],[],{alloc,R,{zero,Ns,Nh,[]}}}; collect({init,D}) -> {set,[D],[],init}; collect({test_heap,N,R}) -> {set,[],[],{alloc,R,{nozero,nostack,N,[]}}}; -collect({bif,N,F,As,D}) -> {set,[D],As,{bif,N,F}}; -collect({gc_bif,N,F,R,As,D}) -> {set,[D],As,{alloc,R,{gc_bif,N,F}}}; +collect({bif,N,{f,0},As,D}) -> {set,[D],As,{bif,N,{f,0}}}; +collect({gc_bif,N,{f,0},R,As,D}) -> {set,[D],As,{alloc,R,{gc_bif,N,{f,0}}}}; collect({move,S,D}) -> {set,[D],[S],move}; collect({put_list,S1,S2,D}) -> {set,[D],[S1,S2],put_list}; collect({put_tuple,A,D}) -> {set,[D],[],{put_tuple,A}}; collect({put,S}) -> {set,[],[S],put}; +collect({put_tuple2,D,{list,Els}}) -> {set,[D],Els,put_tuple2}; collect({get_tuple_element,S,I,D}) -> {set,[D],[S],{get_tuple_element,I}}; collect({set_tuple_element,S,D,I}) -> {set,[],[S,D],{set_tuple_element,I}}; collect({get_hd,S,D}) -> {set,[D],[S],get_hd}; collect({get_tl,S,D}) -> {set,[D],[S],get_tl}; collect(remove_message) -> {set,[],[],remove_message}; -collect({put_map,F,Op,S,D,R,{list,Puts}}) -> - {set,[D],[S|Puts],{alloc,R,{put_map,Op,F}}}; -collect({'catch'=Op,R,L}) -> - {set,[R],[],{try_catch,Op,L}}; -collect({'try'=Op,R,L}) -> - {set,[R],[],{try_catch,Op,L}}; +collect({put_map,{f,0},Op,S,D,R,{list,Puts}}) -> + {set,[D],[S|Puts],{alloc,R,{put_map,Op,{f,0}}}}; collect(fclearerror) -> {set,[],[],fclearerror}; collect({fcheckerror,{f,0}}) -> {set,[],[],fcheckerror}; collect({fmove,S,D}) -> {set,[D],[S],fmove}; @@ -137,557 +114,6 @@ embed_lines([{block,B2},{line,_}=Line,{block,B1}|T], Acc) -> embed_lines([{block,B1},{line,_}=Line|T], Acc) -> B = {block,[{set,[],[],Line}|B1]}, embed_lines([B|T], Acc); -embed_lines([{block,B2},{block,B1}|T], Acc) -> - %% This can only happen when beam_block is run for - %% the second time. - B = {block,B1++B2}, - embed_lines([B|T], Acc); embed_lines([I|Is], Acc) -> embed_lines(Is, [I|Acc]); embed_lines([], Acc) -> Acc. - -opt_blocks([{block,Bl0}|Is]) -> - %% The live annotation at the beginning is not useful. - [{'%anno',_}|Bl] = Bl0, - [{block,opt_block(Bl)}|opt_blocks(Is)]; -opt_blocks([I|Is]) -> - [I|opt_blocks(Is)]; -opt_blocks([]) -> []. - -opt_block(Is0) -> - find_fixpoint(fun(Is) -> - opt_tuple_element(opt(Is)) - end, Is0). - -find_fixpoint(OptFun, Is0) -> - case OptFun(Is0) of - Is0 -> Is0; - Is1 -> find_fixpoint(OptFun, Is1) - end. - -%% move_allocates(Is0) -> Is -%% Move allocate instructions upwards in the instruction stream -%% (within the same block), in the hope of getting more possibilities -%% for optimizing away moves later. -%% -%% For example, we can transform the following instructions: -%% -%% get_tuple_element x(1) Element => x(2) -%% allocate_zero StackSize 3 %% x(0), x(1), x(2) are live -%% -%% to the following instructions: -%% -%% allocate_zero StackSize 2 %% x(0) and x(1) are live -%% get_tuple_element x(1) Element => x(2) -%% -%% NOTE: Since the beam_reorder pass has been run, it is no longer -%% safe to assume that if x(N) is initialized, then all lower-numbered -%% x registers are also initialized. -%% -%% For example, we must be careful when transforming the following -%% instructions: -%% -%% get_tuple_element x(0) Element => x(1) -%% allocate_zero StackSize 3 %x(0), x(1), x(2) are live -%% -%% to the following instructions: -%% -%% allocate_zero StackSize 3 -%% get_tuple_element x(0) Element => x(1) -%% -%% The transformation is safe if and only if x(1) has been -%% initialized previously. We will use the annotations added by -%% beam_utils:anno_defs/1 to determine whether x(a) has been -%% initialized. - -move_allocates([{block,Bl0}|Is]) -> - Bl = move_allocates_1(reverse(Bl0), []), - [{block,Bl}|move_allocates(Is)]; -move_allocates([I|Is]) -> - [I|move_allocates(Is)]; -move_allocates([]) -> []. - -move_allocates_1([{'%anno',_}|Is], Acc) -> - move_allocates_1(Is, Acc); -move_allocates_1([I|Is], [{set,[],[],{alloc,Live0,Info0}}|Acc]=Acc0) -> - case alloc_may_pass(I) of - false -> - move_allocates_1(Is, [I|Acc0]); - true -> - case alloc_live_regs(I, Is, Live0) of - not_possible -> - move_allocates_1(Is, [I|Acc0]); - Live when is_integer(Live) -> - Info = safe_info(Info0), - A = {set,[],[],{alloc,Live,Info}}, - move_allocates_1(Is, [A,I|Acc]) - end - end; -move_allocates_1([I|Is], Acc) -> - move_allocates_1(Is, [I|Acc]); -move_allocates_1([], Acc) -> Acc. - -alloc_may_pass({set,_,[{fr,_}],fmove}) -> false; -alloc_may_pass({set,_,_,{alloc,_,_}}) -> false; -alloc_may_pass({set,_,_,{set_tuple_element,_}}) -> false; -alloc_may_pass({set,_,_,put_list}) -> false; -alloc_may_pass({set,_,_,put}) -> false; -alloc_may_pass({set,_,_,_}) -> true. - -safe_info({nozero,Stack,Heap,_}) -> - %% nozero is not safe if the allocation instruction is moved - %% upwards past an instruction that may throw an exception - %% (such as element/2). - {zero,Stack,Heap,[]}; -safe_info(Info) -> Info. - -%% opt([Instruction]) -> [Instruction] -%% Optimize the instruction stream inside a basic block. - -opt([{set,[X],[X],move}|Is]) -> opt(Is); -opt([{set,[Dst],_,move},{set,[Dst],[Src],move}=I|Is]) when Dst =/= Src -> - opt([I|Is]); -opt([{set,[{x,0}],[S1],move}=I1,{set,[D2],[{x,0}],move}|Is]) -> - opt([I1,{set,[D2],[S1],move}|Is]); -opt([{set,[{x,0}],[S1],move}=I1,{set,[D2],[S2],move}|Is0]) when S1 =/= D2 -> - %% Place move S x0 at the end of move sequences so that - %% loader can merge with the following instruction - {Ds,Is} = opt_moves([D2], Is0), - [{set,Ds,[S2],move}|opt([I1|Is])]; -opt([{set,_,_,{line,_}}=Line1, - {set,[D1],[{integer,Idx1},Reg],{bif,element,{f,0}}}=I1, - {set,_,_,{line,_}}=Line2, - {set,[D2],[{integer,Idx2},Reg],{bif,element,{f,0}}}=I2|Is]) - when Idx1 < Idx2, D1 =/= D2, D1 =/= Reg, D2 =/= Reg -> - opt([Line2,I2,Line1,I1|Is]); -opt([{set,[D1],[{integer,Idx1},Reg],{bif,element,{f,L}}}=I1, - {set,[D2],[{integer,Idx2},Reg],{bif,element,{f,L}}}=I2|Is]) - when Idx1 < Idx2, D1 =/= D2, D1 =/= Reg, D2 =/= Reg -> - opt([I2,I1|Is]); -opt([{set,Hd0,Cons,get_hd}=GetHd, - {set,Tl0,Cons,get_tl}=GetTl|Is0]) -> - case {opt_moves(Hd0, [GetTl|Is0]),opt_moves(Tl0, [GetHd|Is0])} of - {{Hd0,Is},{Tl0,_}} -> - [GetHd|opt(Is)]; - {{Hd,Is},{Tl0,_}} -> - [{set,Hd,Cons,get_hd}|opt(Is)]; - {{_,_},{Tl,Is}} -> - [{set,Tl,Cons,get_tl}|opt(Is)] - end; -opt([{set,Ds0,Ss,Op}|Is0]) -> - {Ds,Is} = opt_moves(Ds0, Is0), - [{set,Ds,Ss,Op}|opt(Is)]; -opt([{'%anno',_}=I|Is]) -> - [I|opt(Is)]; -opt([]) -> []. - -%% opt_moves([Dest], [Instruction]) -> {[Dest],[Instruction]} -%% For each Dest, does the optimization described in opt_move/2. - -opt_moves([], Is0) -> {[],Is0}; -opt_moves([D0]=Ds, Is0) -> - case opt_move(D0, Is0) of - not_possible -> {Ds,Is0}; - {D1,Is} -> {[D1],Is} - end. - -%% opt_move(Dest, [Instruction]) -> {UpdatedDest,[Instruction]} | not_possible -%% If there is a {move,Dest,FinalDest} instruction -%% in the instruction stream, remove the move instruction -%% and let FinalDest be the destination. - -opt_move(Dest, Is) -> - opt_move_1(Dest, Is, []). - -opt_move_1(R, [{set,[D],[R],move}|Is0], Acc) -> - %% Provided that the source register is killed by instructions - %% that follow, the optimization is safe. - case eliminate_use_of_from_reg(Is0, R, D) of - {yes,Is} -> opt_move_rev(D, Acc, Is); - no -> not_possible - end; -opt_move_1(_R, [{set,_,_,{alloc,_,_}}|_], _) -> - %% The optimization is either not possible or not safe. - %% - %% If R is an X register killed by allocation, the optimization is - %% not safe. On the other hand, if the X register is killed, there - %% will not follow a 'move' instruction with this X register as - %% the source. - %% - %% If R is a Y register, the optimization is still not safe - %% because the new target register is an X register that cannot - %% safely pass the alloc instruction. - not_possible; -opt_move_1(R, [{set,_,_,_}=I|Is], Acc) -> - %% If the source register is either killed or used by this - %% instruction, the optimimization is not possible. - case is_killed_or_used(R, I) of - true -> not_possible; - false -> opt_move_1(R, Is, [I|Acc]) - end; -opt_move_1(_, _, _) -> - not_possible. - -%% opt_tuple_element([Instruction]) -> [Instruction] -%% If possible, move get_tuple_element instructions forward -%% in the instruction stream to a move instruction, eliminating -%% the move instruction. Example: -%% -%% get_tuple_element Tuple Pos Dst1 -%% ... -%% move Dst1 Dst2 -%% -%% This code may be possible to rewrite to: -%% -%% %%(Moved get_tuple_element instruction) -%% ... -%% get_tuple_element Tuple Pos Dst2 -%% - -opt_tuple_element([{set,[D],[S],{get_tuple_element,_}}=I|Is0]) -> - case opt_tuple_element_1(Is0, I, {S,D}, []) of - no -> - [I|opt_tuple_element(Is0)]; - {yes,Is} -> - opt_tuple_element(Is) - end; -opt_tuple_element([I|Is]) -> - [I|opt_tuple_element(Is)]; -opt_tuple_element([]) -> []. - -opt_tuple_element_1([{set,_,_,{alloc,_,_}}|_], _, _, _) -> - no; -opt_tuple_element_1([{set,_,_,{try_catch,_,_}}|_], _, _, _) -> - no; -opt_tuple_element_1([{set,[D],[S],move}|Is0], I0, {_,S}, Acc) -> - case eliminate_use_of_from_reg(Is0, S, D) of - no -> - no; - {yes,Is1} -> - {set,[S],Ss,Op} = I0, - I = {set,[D],Ss,Op}, - case opt_move_rev(S, Acc, [I|Is1]) of - not_possible -> - %% Not safe because the move of the - %% get_tuple_element instruction would cause the - %% result of a previous instruction to be ignored. - no; - {_,Is} -> - {yes,Is} - end - end; -opt_tuple_element_1([{set,Ds,Ss,_}=I|Is], MovedI, {S,D}=Regs, Acc) -> - case member(S, Ds) orelse member(D, Ss) of - true -> - no; - false -> - opt_tuple_element_1(Is, MovedI, Regs, [I|Acc]) - end; -opt_tuple_element_1(_, _, _, _) -> no. - -%% Reverse the instructions, while checking that there are no -%% instructions that would interfere with using the new destination -%% register (D). - -opt_move_rev(D, [I|Is], Acc) -> - case is_killed_or_used(D, I) of - true -> not_possible; - false -> opt_move_rev(D, Is, [I|Acc]) - end; -opt_move_rev(D, [], Acc) -> {D,Acc}. - -%% is_killed_or_used(Register, {set,_,_,_}) -> bool() -%% Test whether the register is used by the instruction. - -is_killed_or_used(R, {set,Ss,Ds,_}) -> - member(R, Ds) orelse member(R, Ss). - -%% eliminate_use_of_from_reg([Instruction], FromRegister, ToRegister, Acc) -> -%% {yes,Is} | no -%% Eliminate any use of FromRegister in the instruction sequence -%% by replacing uses of FromRegister with ToRegister. If FromRegister -%% is referenced by an allocation instruction, return 'no' to indicate -%% that FromRegister is still used and that the optimization is not -%% possible. - -eliminate_use_of_from_reg(Is, From, To) -> - try - eliminate_use_of_from_reg(Is, From, To, []) - catch - throw:not_possible -> - no - end. - -eliminate_use_of_from_reg([{set,_,_,{alloc,Live,_}}|_]=Is0, {x,X}, _, Acc) -> - if - X < Live -> - no; - true -> - {yes,reverse(Acc, Is0)} - end; -eliminate_use_of_from_reg([{set,Ds,Ss0,Op}=I0|Is], From, To, Acc) -> - ensure_safe_tuple(I0, To), - I = case member(From, Ss0) of - true -> - Ss = [case S of - From -> To; - _ -> S - end || S <- Ss0], - {set,Ds,Ss,Op}; - false -> - I0 - end, - case member(From, Ds) of - true -> - {yes,reverse(Acc, [I|Is])}; - false -> - case member(To, Ds) of - true -> - case beam_utils:is_killed_block(From, Is) of - true -> - {yes,reverse(Acc, [I|Is])}; - false -> - no - end; - false -> - eliminate_use_of_from_reg(Is, From, To, [I|Acc]) - end - end; -eliminate_use_of_from_reg([I]=Is, From, _To, Acc) -> - case beam_utils:is_killed_block(From, [I]) of - true -> - {yes,reverse(Acc, Is)}; - false -> - no - end. - -ensure_safe_tuple({set,[To],[],{put_tuple,_}}, To) -> - throw(not_possible); -ensure_safe_tuple(_, _) -> ok. - -%% opt_allocs(Instructions) -> Instructions. Optimize allocate -%% instructions inside blocks. If safe, replace an allocate_zero -%% instruction with the slightly cheaper allocate instruction. - -opt_allocs(Is) -> - D = beam_utils:index_labels(Is), - opt_allocs_1(Is, D). - -opt_allocs_1([{block,Bl0}|Is], D) -> - Bl = opt_alloc(Bl0, {D,Is}), - [{block,Bl}|opt_allocs_1(Is, D)]; -opt_allocs_1([I|Is], D) -> - [I|opt_allocs_1(Is, D)]; -opt_allocs_1([], _) -> []. - -%% opt_alloc(Instructions) -> Instructions' -%% Optimises all allocate instructions. - -opt_alloc([{set,[],[],{alloc,Live0,Info0}}, - {set,[],[],{alloc,Live,Info}}|Is], D) -> - Live = Live0, %Assertion. - Alloc = combine_alloc(Info0, Info), - I = {set,[],[],{alloc,Live,Alloc}}, - opt_alloc([I|Is], D); -opt_alloc([{set,[],[],{alloc,R,{_,Ns,Nh,[]}}}|Is], D) -> - [{set,[],[],opt_alloc(Is, D, Ns, Nh, R)}|Is]; -opt_alloc([I|Is], D) -> [I|opt_alloc(Is, D)]; -opt_alloc([], _) -> []. - -combine_alloc({_,Ns,Nh1,Init}, {_,nostack,Nh2,[]}) -> - {zero,Ns,beam_utils:combine_heap_needs(Nh1, Nh2),Init}. - -%% opt_alloc(Instructions, FrameSize, HeapNeed, LivingRegs) -> [Instr] -%% Generates the optimal sequence of instructions for -%% allocating and initalizing the stack frame and needed heap. - -opt_alloc(_Is, _D, nostack, Nh, LivingRegs) -> - {alloc,LivingRegs,{nozero,nostack,Nh,[]}}; -opt_alloc(Bl, {D,OuterIs}, Ns, Nh, LivingRegs) -> - Is = [{block,Bl}|OuterIs], - InitRegs = init_yregs(Ns, Is, D), - case count_ones(InitRegs) of - N when N*2 > Ns -> - {alloc,LivingRegs,{nozero,Ns,Nh,gen_init(Ns, InitRegs)}}; - _ -> - {alloc,LivingRegs,{zero,Ns,Nh,[]}} - end. - -gen_init(Fs, Regs) -> gen_init(Fs, Regs, 0, []). - -gen_init(SameFs, _Regs, SameFs, Acc) -> reverse(Acc); -gen_init(Fs, Regs, Y, Acc) when Regs band 1 =:= 0 -> - gen_init(Fs, Regs bsr 1, Y+1, [{init,{y,Y}}|Acc]); -gen_init(Fs, Regs, Y, Acc) -> - gen_init(Fs, Regs bsr 1, Y+1, Acc). - -init_yregs(Y, Is, D) when Y >= 0 -> - case beam_utils:is_killed({y,Y}, Is, D) of - true -> - (1 bsl Y) bor init_yregs(Y-1, Is, D); - false -> - init_yregs(Y-1, Is, D) - end; -init_yregs(_, _, _) -> 0. - -count_ones(Bits) -> count_ones(Bits, 0). -count_ones(0, Acc) -> Acc; -count_ones(Bits, Acc) -> - count_ones(Bits bsr 1, Acc + (Bits band 1)). - -%% Calculate the new number of live registers when we move an allocate -%% instruction upwards, passing a 'set' instruction. - -alloc_live_regs({set,Ds,Ss,_}, Is, Regs0) -> - Rset = x_live(Ss, x_dead(Ds, (1 bsl Regs0)-1)), - Live = live_regs(0, Rset), - case ensure_contiguous(Rset, Live) of - not_possible -> - %% Liveness information (looking forward in the - %% instruction stream) can't prove that moving this - %% allocation instruction is safe. Now use the annotation - %% of defined registers at the beginning of the current - %% block to see whether moving would be safe. - Def0 = defined_regs(Is, 0), - Def = Def0 band ((1 bsl Live) - 1), - ensure_contiguous(Rset bor Def, Live); - Live -> - %% Safe based on liveness information. - Live - end. - -live_regs(N, 0) -> - N; -live_regs(N, Regs) -> - live_regs(N+1, Regs bsr 1). - -ensure_contiguous(Regs, Live) -> - case (1 bsl Live) - 1 of - Regs -> Live; - _ -> not_possible - end. - -x_dead([{x,N}|Rs], Regs) -> x_dead(Rs, Regs band (bnot (1 bsl N))); -x_dead([_|Rs], Regs) -> x_dead(Rs, Regs); -x_dead([], Regs) -> Regs. - -x_live([{x,N}|Rs], Regs) -> x_live(Rs, Regs bor (1 bsl N)); -x_live([_|Rs], Regs) -> x_live(Rs, Regs); -x_live([], Regs) -> Regs. - -%% defined_regs(ReversedInstructions) -> RegBitmap. -%% Given a reversed instruction stream, determine the -%% the registers that are defined. - -defined_regs([{'%anno',{def,Def}}|_], Regs) -> - Def bor Regs; -defined_regs([{set,Ds,_,{alloc,Live,_}}|_], Regs) -> - x_live(Ds, Regs bor ((1 bsl Live) - 1)); -defined_regs([{set,Ds,_,_}|Is], Regs) -> - defined_regs(Is, x_live(Ds, Regs)). - -%%% -%%% Do local common sub expression elimination (CSE) in each block. -%%% - -local_cse([{block,Bl0}|Is]) -> - Bl = cse_block(Bl0, orddict:new(), []), - [{block,Bl}|local_cse(Is)]; -local_cse([I|Is]) -> - [I|local_cse(Is)]; -local_cse([]) -> []. - -cse_block([I|Is], Es0, Acc0) -> - Es1 = cse_clear(I, Es0), - case cse_expr(I) of - none -> - %% Instruction is not suitable for CSE. - cse_block(Is, Es1, [I|Acc0]); - {ok,D,Expr} -> - %% Suitable instruction. First update the dictionary of - %% suitable expressions for the next iteration. - Es = cse_add(D, Expr, Es1), - - %% Search for a previous identical expression. - case cse_find(Expr, Es0) of - error -> - %% Nothing found - cse_block(Is, Es, [I|Acc0]); - Src -> - %% Use the previously calculated result. - %% Also eliminate any line instruction. - Move = {set,[D],[Src],move}, - case Acc0 of - [{set,_,_,{line,_}}|Acc] -> - cse_block(Is, Es, [Move|Acc]); - [_|_] -> - cse_block(Is, Es, [Move|Acc0]) - end - end - end; -cse_block([], _, Acc) -> - reverse(Acc). - -%% cse_find(Expr, Expressions) -> error | Register. -%% Find a previously evaluated expression whose result can be reused, -%% or return 'error' if no such expression is found. - -cse_find(Expr, Es) -> - case orddict:find(Expr, Es) of - {ok,{Src,_}} -> Src; - error -> error - end. - -cse_expr({set,[D],Ss,{bif,N,_}}) -> - case D of - {fr,_} -> - %% There are too many things that can go wrong. - none; - _ -> - {ok,D,{{bif,N},Ss}} - end; -cse_expr({set,[D],Ss,{alloc,_,{gc_bif,N,_}}}) -> - {ok,D,{{gc_bif,N},Ss}}; -cse_expr({set,[D],Ss,put_list}) -> - {ok,D,{put_list,Ss}}; -cse_expr(_) -> none. - -%% cse_clear(Instr, Expressions0) -> Expressions. -%% Remove all previous expressions that will become -%% invalid when this instruction is executed. Basically, -%% an expression is no longer safe to reuse when the -%% register it has been stored to has been modified, killed, -%% or if any of the source operands have changed. - -cse_clear({set,Ds,_,{alloc,Live,_}}, Es) -> - cse_clear_1(Es, Live, Ds); -cse_clear({set,Ds,_,_}, Es) -> - cse_clear_1(Es, all, Ds). - -cse_clear_1(Es, Live, Ds0) -> - Ds = ordsets:from_list(Ds0), - [E || E <- Es, cse_is_safe(E, Live, Ds)]. - -cse_is_safe({_,{Dst,Interfering}}, Live, Ds) -> - ordsets:is_disjoint(Interfering, Ds) andalso - case Dst of - {x,X} -> - X < Live; - _ -> - true - end. - -%% cse_add(Dest, Expr, Expressions0) -> Expressions. -%% Provided that it is safe, add a new expression to the dictionary -%% of already evaluated expressions. - -cse_add(D, {_,Ss}=Expr, Es) -> - case member(D, Ss) of - false -> - Interfering = ordsets:from_list([D|Ss]), - orddict:store(Expr, {D,Interfering}, Es); - true -> - %% Unsafe because the instruction overwrites one of - %% source operands. - Es - end. |