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%%
%% %CopyrightBegin%
%%
%% Copyright Ericsson AB 1999-2018. All Rights Reserved.
%%
%% Licensed under the Apache License, Version 2.0 (the "License");
%% you may not use this file except in compliance with the License.
%% You may obtain a copy of the License at
%%
%% http://www.apache.org/licenses/LICENSE-2.0
%%
%% Unless required by applicable law or agreed to in writing, software
%% distributed under the License is distributed on an "AS IS" BASIS,
%% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
%% See the License for the specific language governing permissions and
%% limitations under the License.
%%
%% %CopyrightEnd%
%%
%% Purpose: Partition BEAM instructions into basic blocks.
-module(beam_block).
-export([module/2]).
-import(lists, [keysort/2,reverse/1,reverse/2,splitwith/2]).
-spec module(beam_utils:module_code(), [compile:option()]) ->
{'ok',beam_utils:module_code()}.
module({Mod,Exp,Attr,Fs0,Lc}, _Opts) ->
Fs = [function(F) || F <- Fs0],
{ok,{Mod,Exp,Attr,Fs,Lc}}.
function({function,Name,Arity,CLabel,Is0}) ->
try
Is1 = swap_opt(Is0),
Is2 = blockify(Is1),
Is = embed_lines(Is2),
{function,Name,Arity,CLabel,Is}
catch
Class:Error:Stack ->
io:fwrite("Function: ~w/~w\n", [Name,Arity]),
erlang:raise(Class, Error, Stack)
end.
%%%
%%% Try to use a `swap` instruction instead of a sequence of moves.
%%%
%%% Note that beam_ssa_codegen generates `swap` instructions only for
%%% the moves within a single SSA instruction (such as `call`), not
%%% for the moves generated by a sequence of SSA instructions.
%%% Therefore, this optimization is needed.
%%%
%%% We'll need to handle non-consecutive sequences of moves, such
%%% as the following instruction sequence:
%%%
%%% move y2, x2
%%% move x0, y2
%%% move y1, x1
%%% init_yregs [y1]
%%% move x2, x0
%%%
%%% The first two `move` instructions and the last `move` instruction
%%% should be combined to a `swap` instruction:
%%%
%%% swap y2, x0
%%% move y1, x1
%%% init_yregs [y1]
%%%
%%% (Provided that x2 is killed in the code that follows.)
%%%
swap_opt([{move,Reg1,{x,_}=Temp}=Move1,
{move,Reg2,Reg1}=Move2|Is0]) when Reg1 =/= Temp ->
case swap_opt_end(Is0, Temp, Reg2, []) of
{yes,Is} ->
[{swap,Reg1,Reg2}|swap_opt(Is)];
no ->
[Move1|swap_opt([Move2|Is0])]
end;
swap_opt([I|Is]) ->
[I|swap_opt(Is)];
swap_opt([]) -> [].
swap_opt_end([{move,S,D}=I|Is], Temp, Dst, Acc) ->
case {S,D} of
{Temp,Dst} ->
{x,X} = Temp,
case is_unused(X, Is) of
true -> {yes,reverse(Acc, Is)};
false -> no
end;
{Temp,_} -> no;
{Dst,_} -> no;
{_,Temp} -> no;
{_,Dst} -> no;
{_,_} -> swap_opt_end(Is, Temp, Dst, [I|Acc])
end;
swap_opt_end([{init_yregs,_}=I|Is], Temp, Dst, Acc) ->
swap_opt_end(Is, Temp, Dst, [I|Acc]);
swap_opt_end(_, _, _, _) -> no.
is_unused(X, [{call,A,_}|_]) when A =< X -> true;
is_unused(X, [{call_ext,A,_}|_]) when A =< X -> true;
is_unused(X, [{make_fun2,_,_,_,A}|_]) when A =< X -> true;
is_unused(X, [{move,Src,Dst}|Is]) ->
case {Src,Dst} of
{{x,X},_} -> false;
{_,{x,X}} -> true;
{_,_} -> is_unused(X, Is)
end;
is_unused(X, [{line,_}|Is]) -> is_unused(X, Is);
is_unused(_, _) -> false.
%% blockify(Instructions0) -> Instructions
%% Collect sequences of instructions to basic blocks.
%% Also do some simple optimations on instructions outside the blocks.
blockify(Is) ->
blockify(Is, []).
blockify([I|Is0]=IsAll, Acc) ->
case collect(I) of
error -> blockify(Is0, [I|Acc]);
Instr when is_tuple(Instr) ->
{Block0,Is} = collect_block(IsAll),
Block = sort_moves(Block0),
blockify(Is, [{block,Block}|Acc])
end;
blockify([], Acc) -> reverse(Acc).
collect_block(Is) ->
collect_block(Is, []).
collect_block([{allocate,N,R}|Is0], Acc) ->
{Inits,Is} = splitwith(fun ({init,{y,_}}) -> true;
(_) -> false
end, Is0),
collect_block(Is, [{set,[],[],{alloc,R,{nozero,N,0,Inits}}}|Acc]);
collect_block([I|Is]=Is0, Acc) ->
case collect(I) of
error -> {reverse(Acc),Is0};
Instr -> collect_block(Is, [Instr|Acc])
end;
collect_block([], Acc) ->
{reverse(Acc),[]}.
collect({allocate,N,R}) -> {set,[],[],{alloc,R,{nozero,N,0,[]}}};
collect({allocate_heap,Ns,Nh,R}) -> {set,[],[],{alloc,R,{nozero,Ns,Nh,[]}}};
collect({test_heap,N,R}) -> {set,[],[],{alloc,R,{nozero,nostack,N,[]}}};
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,0},Op,S,D,R,{list,Puts}}) ->
{set,[D],[S|Puts],{alloc,R,{put_map,Op,{f,0}}}};
collect({fmove,S,D}) -> {set,[D],[S],fmove};
collect({fconv,S,D}) -> {set,[D],[S],fconv};
collect(_) -> error.
%% embed_lines([Instruction]) -> [Instruction]
%% Combine blocks that would be split by line/1 instructions.
%% Also move a line instruction before a block into the block,
%% but leave the line/1 instruction after a block outside.
embed_lines(Is) ->
embed_lines(reverse(Is), []).
embed_lines([{block,B2},{line,_}=Line,{block,B1}|T], Acc) ->
B = {block,B1++[{set,[],[],Line}]++B2},
embed_lines([B|T], Acc);
embed_lines([{block,B1},{line,_}=Line|T], Acc) ->
B = {block,[{set,[],[],Line}|B1]},
embed_lines([B|T], Acc);
embed_lines([I|Is], Acc) ->
embed_lines(Is, [I|Acc]);
embed_lines([], Acc) -> Acc.
%% sort_moves([Instruction]) -> [Instruction].
%% Sort move instructions on the Y register to give the loader
%% more opportunities for combining instructions.
sort_moves([{set,[{x,_}],[{y,_}],move}=I|Is0]) ->
{Moves,Is} = sort_moves_1(Is0, x, y, [I]),
Moves ++ sort_moves(Is);
sort_moves([{set,[{y,_}],[{x,_}],move}=I|Is0]) ->
{Moves,Is} = sort_moves_1(Is0, y, x, [I]),
Moves ++ sort_moves(Is);
sort_moves([I|Is]) ->
[I|sort_moves(Is)];
sort_moves([]) -> [].
sort_moves_1([{set,[{x,0}],[_],move}=I|Is], _DTag, _STag, Acc) ->
%% The loader sometimes combines a move to x0 with the
%% instruction that follows, producing, for example, a move_call
%% instruction. Therefore, we don't want include this move
%% instruction in the sorting.
{sort_on_yreg(Acc)++[I],Is};
sort_moves_1([{set,[{DTag,_}],[{STag,_}],move}=I|Is], DTag, STag, Acc) ->
sort_moves_1(Is, DTag, STag, [I|Acc]);
sort_moves_1(Is, _DTag, _STag, Acc) ->
{sort_on_yreg(Acc),Is}.
sort_on_yreg([{set,[Dst],[Src],move}|_]=Moves) ->
case {Dst,Src} of
{{y,_},{x,_}} ->
keysort(2, Moves);
{{x,_},{y,_}} ->
keysort(3, Moves)
end.
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