%%
%% %CopyrightBegin%
%%
%% Copyright Ericsson AB 2004-2016. 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: Optimizes booleans in guards.
-module(beam_bool).
-export([module/2]).
-import(lists, [reverse/1,reverse/2,foldl/3,mapfoldl/3,map/2]).
-record(st,
{next, %Next label number.
ll %Live regs at labels.
}).
module({Mod,Exp,Attr,Fs0,Lc}, _Opts) ->
%%io:format("~p:\n", [Mod]),
{Fs,_} = mapfoldl(fun(Fn, Lbl) -> function(Fn, Lbl) end, 100000000, Fs0),
{ok,{Mod,Exp,Attr,Fs,Lc}}.
function({function,Name,Arity,CLabel,Is0}, Lbl0) ->
try
{Is,#st{next=Lbl}} = bool_opt(Is0, Lbl0),
{{function,Name,Arity,CLabel,Is},Lbl}
catch
Class:Error ->
Stack = erlang:get_stacktrace(),
io:fwrite("Function: ~w/~w\n", [Name,Arity]),
erlang:raise(Class, Error, Stack)
end.
%%
%% Optimize boolean expressions that use guard bifs. Rewrite to
%% use test instructions if possible.
%%
bool_opt(Asm, Lbl) ->
LiveInfo = beam_utils:index_labels(Asm),
bopt(Asm, [], #st{next=Lbl,ll=LiveInfo}).
bopt([{block,Bl0}=Block|
[{jump,{f,Succ}},
{label,Fail},
{block,[{set,[Dst],[{atom,false}],move}]},
{label,Succ}|Is]=Is0], Acc0, St) ->
case split_block(Bl0, Dst, Fail, Acc0, true) of
failed ->
bopt(Is0, [Block|Acc0], St);
{Bl,PreBlock} ->
Acc1 = case PreBlock of
[] -> Acc0;
_ -> [{block,PreBlock}|Acc0]
end,
Acc = [{protected,[Dst],Bl,{Fail,Succ}}|Acc1],
bopt(Is, Acc, St)
end;
bopt([{test,is_eq_exact,{f,Fail},[Reg,{atom,true}]}=I|Is], [{block,_}|_]=Acc0, St0) ->
case bopt_block(Reg, Fail, Is, Acc0, St0) of
failed -> bopt(Is, [I|Acc0], St0);
{Acc,St} -> bopt(Is, Acc, St)
end;
bopt([I|Is], Acc, St) ->
bopt(Is, [I|Acc], St);
bopt([], Acc, St) ->
{bopt_reverse(Acc, []),St}.
bopt_reverse([{protected,[Dst],Block,{Fail,Succ}}|Is], Acc0) ->
Acc = [{block,Block},{jump,{f,Succ}},
{label,Fail},
{block,[{set,[Dst],[{atom,false}],move}]},
{label,Succ}|Acc0],
bopt_reverse(Is, Acc);
bopt_reverse([I|Is], Acc) ->
bopt_reverse(Is, [I|Acc]);
bopt_reverse([], Acc) -> Acc.
%% bopt_block(Reg, Fail, OldIs, Accumulator, St) -> failed | {NewAcc,St}
%% Attempt to optimized a block of guard BIFs followed by a test
%% instruction.
bopt_block(Reg, Fail, OldIs, [{block,Bl0}|Acc0], St0) ->
case split_block(Bl0, Reg, Fail, Acc0, false) of
failed ->
%% Reason for failure: The block either contained no
%% guard BIFs with the failure label Fail, or the final
%% instruction in the block did not assign the Reg register.
%%io:format("split ~p: ~P\n", [Reg,Bl0,20]),
failed;
{Bl1,BlPre} ->
%% The block has been splitted. Bl1 is a non-empty list
%% of guard BIF instructions having the failure label Fail.
%% BlPre is a (possibly empty list) of instructions preceeding
%% Bl1.
Acc1 = make_block(BlPre, Acc0),
{Bl,Acc} = extend_block(Bl1, Fail, Acc1),
try
{NewCode,St} = bopt_tree_cg(Bl, Fail, St0),
ensure_opt_safe(Bl, NewCode, OldIs, Fail, Acc, St),
{NewCode++Acc,St}
catch
%% Not possible to rewrite because a boolean value is
%% passed to another guard bif, e.g. 'abs(A > B)'
%% (in this case, obviously nonsense code). Rare in
%% practice.
throw:mixed ->
failed;
%% There was a reference to a boolean expression
%% from inside a protected block (try/catch), to
%% a boolean expression outside.
throw:protected_barrier ->
failed;
%% The 'xor' operator was used. We currently don't
%% find it worthwile to translate 'xor' operators
%% (the code would be clumsy).
throw:'xor' ->
failed;
%% The block does not contain a boolean expression,
%% but only a call to a guard BIF.
%% For instance: ... when element(1, T) ->
throw:not_boolean_expr ->
failed;
%% The optimization is not safe. (A register
%% used by the instructions following the
%% optimized code is either not assigned a
%% value at all or assigned a different value.)
throw:all_registers_not_killed ->
failed;
throw:registers_used ->
failed;
%% A protected block refered to the value
%% returned by another protected block,
%% probably because the Core Erlang code
%% used nested try/catches in the guard.
%% (v3_core never produces nested try/catches
%% in guards, so it must have been another
%% Core Erlang translator.)
throw:protected_violation ->
failed;
%% Failed to work out the live registers for a GC
%% BIF. For example, if the number of live registers
%% needed to be 4 because {x,3} was a source register,
%% but {x,2} was not known to be initialized, this
%% exception would be thrown.
throw:gc_bif_alloc_failure ->
failed
end
end.
%% ensure_opt_safe(OriginalCode, OptCode, FollowingCode, Fail,
%% ReversedPrecedingCode, State) -> ok
%% Comparing the original code to the optimized code, determine
%% whether the optimized code is guaranteed to work in the same
%% way as the original code.
%%
%% Throw an exception if the optimization is not safe.
%%
ensure_opt_safe(Bl, NewCode, OldIs, Fail, PrecedingCode, St) ->
%% Here are the conditions that must be true for the
%% optimization to be safe.
%%
%% 1. If a register is INITIALIZED by PrecedingCode,
%% then if that register assigned a value in the original
%% code, but not in the optimized code, it must be UNUSED or KILLED
%% in the code that follows.
%%
%% 2. If a register is not known to be INITIALIZED by PreccedingCode,
%% then if that register assigned a value in the original
%% code, but not in the optimized code, it must be KILLED
%% by the code that follows.
%%
%% 3. Any register that is assigned a value in the optimized
%% code must be UNUSED or KILLED in the following code,
%% unless we can be sure that it is always assigned the same
%% value.
InitInPreceding = initialized_regs(PrecedingCode),
PrevDst = dst_regs(Bl),
NewDst = dst_regs(NewCode),
NotSet = ordsets:subtract(PrevDst, NewDst),
MustBeKilled = ordsets:subtract(NotSet, InitInPreceding),
case all_killed(MustBeKilled, OldIs, Fail, St) of
false -> throw(all_registers_not_killed);
true -> ok
end,
MustBeUnused = ordsets:subtract(ordsets:union(NotSet, NewDst),
MustBeKilled),
case none_used(MustBeUnused, OldIs, Fail, St) of
false -> throw(registers_used);
true -> ok
end,
ok.
update_fail_label([{set,Ds,As,{bif,N,{f,_}}}|Is], Fail, Acc) ->
update_fail_label(Is, Fail, [{set,Ds,As,{bif,N,{f,Fail}}}|Acc]);
update_fail_label([{set,Ds,As,{alloc,Regs,{gc_bif,N,{f,_}}}}|Is], Fail, Acc) ->
update_fail_label(Is, Fail,
[{set,Ds,As,{alloc,Regs,{gc_bif,N,{f,Fail}}}}|Acc]);
update_fail_label([], _, Acc) -> reverse(Acc).
make_block(Bl) ->
make_block(Bl, []).
make_block([], Acc) -> Acc;
make_block(Bl, Acc) -> [{block,Bl}|Acc].
extend_block(BlAcc, Fail, [{protected,_,_,_}=Prot|OldAcc]) ->
extend_block([Prot|BlAcc], Fail, OldAcc);
extend_block(BlAcc0, Fail, [{block,Is0}|OldAcc]) ->
case extend_block_1(reverse(Is0), Fail, BlAcc0) of
{BlAcc,[]} -> extend_block(BlAcc, Fail, OldAcc);
{BlAcc,Is} -> {BlAcc,[{block,Is}|OldAcc]}
end;
extend_block(BlAcc, _, OldAcc) -> {BlAcc,OldAcc}.
extend_block_1([{set,[{x,_}],_,{bif,_,{f,Fail}}}=I|Is], Fail, Acc) ->
extend_block_1(Is, Fail, [I|Acc]);
extend_block_1([{set,[{x,_}],As,{bif,Bif,_}}=I|Is]=Is0, Fail, Acc) ->
case safe_bool_op(Bif, length(As)) of
false -> {Acc,reverse(Is0)};
true -> extend_block_1(Is, Fail, [I|Acc])
end;
extend_block_1([_|_]=Is, _, Acc) -> {Acc,reverse(Is)};
extend_block_1([], _, Acc) -> {Acc,[]}.
%% split_block([Instruction], Destination, FailLabel, [PreInstruction],
%% ProhibitFailLabelInPreBlock) -> failed | {Block,PreBlock}
%% Split a sequence of instructions into two blocks - one containing
%% all guard bif instructions and a pre-block all instructions before
%% the guard BIFs.
split_block(Is0, Dst, Fail, PreIs, ProhibitFailLabel) ->
case ProhibitFailLabel andalso beam_jump:is_label_used_in(Fail, PreIs) of
true ->
%% The failure label was used in one of the instructions (most
%% probably bit syntax construction) preceeding the block,
%% the caller might eliminate the label.
failed;
false ->
case reverse(Is0) of
[{set,[Dst],_,_}|_]=Is ->
split_block_1(Is, Fail, ProhibitFailLabel);
_ -> failed
end
end.
split_block_1(Is, Fail, ProhibitFailLabel) ->
case split_block_2(Is, Fail, []) of
{[],_} -> failed;
{_,PreBlock}=Res ->
case ProhibitFailLabel andalso
split_block_label_used(PreBlock, Fail) of
true ->
%% The failure label was used in the pre-block;
%% not allowed, because the label may be removed.
failed;
false ->
Res
end
end.
split_block_2([{set,[_],_,{bif,_,{f,Fail}}}=I|Is], Fail, Acc) ->
split_block_2(Is, Fail, [I|Acc]);
split_block_2([{set,[_],_,{alloc,_,{gc_bif,_,{f,Fail}}}}=I|Is], Fail, Acc) ->
split_block_2(Is, Fail, [I|Acc]);
split_block_2(Is0, _, Acc) ->
Is = reverse(Is0),
{Acc,Is}.
split_block_label_used([{set,[_],_,{bif,_,{f,Fail}}}|_], Fail) ->
true;
split_block_label_used([{set,[_],_,{alloc,_,{gc_bif,_,{f,Fail}}}}|_], Fail) ->
true;
split_block_label_used([{set,[_],_,{alloc,_,{put_map,_,{f,Fail}}}}|_], Fail) ->
true;
split_block_label_used([_|Is], Fail) ->
split_block_label_used(Is, Fail);
split_block_label_used([], _) -> false.
dst_regs(Is) ->
dst_regs(Is, []).
dst_regs([{block,Bl}|Is], Acc) ->
dst_regs(Bl, dst_regs(Is, Acc));
dst_regs([{set,[D],_,{bif,_,{f,_}}}|Is], Acc) ->
dst_regs(Is, [D|Acc]);
dst_regs([{set,[D],_,{alloc,_,{gc_bif,_,{f,_}}}}|Is], Acc) ->
dst_regs(Is, [D|Acc]);
dst_regs([{protected,_,Bl,_}|Is], Acc) ->
dst_regs(Bl, dst_regs(Is, Acc));
dst_regs([_|Is], Acc) ->
dst_regs(Is, Acc);
dst_regs([], Acc) -> ordsets:from_list(Acc).
all_killed([R|Rs], OldIs, Fail, St) ->
case is_killed(R, OldIs, Fail, St) of
false -> false;
true -> all_killed(Rs, OldIs, Fail, St)
end;
all_killed([], _, _, _) -> true.
none_used([R|Rs], OldIs, Fail, St) ->
case is_not_used(R, OldIs, Fail, St) of
false -> false;
true -> none_used(Rs, OldIs, Fail, St)
end;
none_used([], _, _, _) -> true.
bopt_tree_cg(Block0, Fail, St) ->
Free = free_variables(Block0),
Block = ssa_block(Block0),
%% io:format("~p\n", [Block0]),
%% io:format("~p\n", [Block]),
%% io:format("~p\n", [gb_trees:to_list(Free)]),
case bopt_tree(Block, Free, []) of
{Pre0,[{_,Tree}]} ->
Pre1 = update_fail_label(Pre0, Fail, []),
Regs0 = init_regs(gb_trees:keys(Free)),
%% io:format("~p\n", [dst_regs(Block0)]),
%% io:format("~p\n", [Pre1]),
%% io:format("~p\n", [Tree]),
%% io:nl(),
{Pre,Regs} = rename_regs(Pre1, Regs0),
%% io:format("~p\n", [Regs0]),
%% io:format("~p\n", [Pre]),
bopt_cg(Tree, Fail, Regs, make_block(Pre), St);
_Res ->
throw(not_boolean_expr)
end.
bopt_tree([{set,[Dst],As0,{bif,'not',_}}|Is], Forest0, Pre) ->
{[Arg],Forest1} = bopt_bool_args(As0, Forest0),
Forest = gb_trees:enter(Dst, {'not',Arg}, Forest1),
bopt_tree(Is, Forest, Pre);
bopt_tree([{set,[Dst],As0,{bif,'and',_}}|Is], Forest0, Pre) ->
{As,Forest1} = bopt_bool_args(As0, Forest0),
Node = make_and_node(As),
Forest = gb_trees:enter(Dst, Node, Forest1),
bopt_tree(Is, Forest, Pre);
bopt_tree([{set,[Dst],As0,{bif,'or',_}}|Is], Forest0, Pre) ->
{As,Forest1} = bopt_bool_args(As0, Forest0),
Node = make_or_node(As),
Forest = gb_trees:enter(Dst, Node, Forest1),
bopt_tree(Is, Forest, Pre);
bopt_tree([{set,_,_,{bif,'xor',_}}|_], _, _) ->
throw('xor');
bopt_tree([{protected,[Dst],Code,_}|Is], Forest0, Pre) ->
ProtForest0 = gb_trees:from_orddict([P || {_,any}=P <- gb_trees:to_list(Forest0)]),
case bopt_tree(Code, ProtForest0, []) of
{ProtPre,[{_,ProtTree}]} ->
Prot = {prot,ProtPre,ProtTree},
Forest = gb_trees:enter(Dst, Prot, Forest0),
bopt_tree(Is, Forest, Pre);
_Res ->
throw(not_boolean_expr)
end;
bopt_tree([{set,[Dst],As,{bif,N,_}}=Bif|Is], Forest0, Pre) ->
Ar = length(As),
case safe_bool_op(N, Ar) of
false ->
bopt_good_args(As, Forest0),
Forest = gb_trees:enter(Dst, any, Forest0),
bopt_tree(Is, Forest, [Bif|Pre]);
true ->
bopt_good_args(As, Forest0),
Test = bif_to_test(Dst, N, As),
Forest = gb_trees:enter(Dst, Test, Forest0),
bopt_tree(Is, Forest, Pre)
end;
bopt_tree([{set,[Dst],As,{alloc,_,{gc_bif,_,_}}}=Bif|Is], Forest0, Pre) ->
bopt_good_args(As, Forest0),
Forest = gb_trees:enter(Dst, any, Forest0),
bopt_tree(Is, Forest, [Bif|Pre]);
bopt_tree([], Forest, Pre) ->
{reverse(Pre),[R || {_,V}=R <- gb_trees:to_list(Forest), V =/= any]}.
safe_bool_op(N, Ar) ->
erl_internal:new_type_test(N, Ar) orelse erl_internal:comp_op(N, Ar).
bopt_bool_args([V0,V0], Forest0) ->
{V,Forest} = bopt_bool_arg(V0, Forest0),
{[V,V],Forest};
bopt_bool_args(As, Forest) ->
mapfoldl(fun bopt_bool_arg/2, Forest, As).
bopt_bool_arg({T,_}=R, Forest) when T =:= x; T =:= y; T =:= tmp ->
Val = case gb_trees:lookup(R, Forest) of
{value,any} -> {test,is_eq_exact,fail,[R,{atom,true}]};
{value,Val0} -> Val0;
none -> throw(mixed)
end,
{Val,gb_trees:delete(R, Forest)};
bopt_bool_arg(Term, Forest) ->
{Term,Forest}.
bopt_good_args([A|As], Regs) ->
bopt_good_arg(A, Regs),
bopt_good_args(As, Regs);
bopt_good_args([], _) -> ok.
bopt_good_arg({Tag,_}=X, Regs) when Tag =:= x; Tag =:= tmp ->
case gb_trees:lookup(X, Regs) of
{value,any} -> ok;
{value,_} -> throw(mixed);
none -> throw(protected_barrier)
end;
bopt_good_arg(_, _) -> ok.
bif_to_test(_, N, As) ->
beam_utils:bif_to_test(N, As, fail).
make_and_node(Is) ->
AndList0 = make_and_list(Is),
case simplify_and_list(AndList0) of
[] -> {atom,true};
[Op] -> Op;
AndList -> {'and',AndList}
end.
make_and_list([{'and',As}|Is]) ->
make_and_list(As++Is);
make_and_list([I|Is]) ->
[I|make_and_list(Is)];
make_and_list([]) -> [].
simplify_and_list([{atom,true}|T]) ->
simplify_and_list(T);
simplify_and_list([{atom,false}=False|_]) ->
[False];
simplify_and_list([H|T]) ->
[H|simplify_and_list(T)];
simplify_and_list([]) -> [].
make_or_node(Is) ->
OrList0 = make_or_list(Is),
case simplify_or_list(OrList0) of
[] -> {atom,false};
[Op] -> Op;
OrList -> {'or',OrList}
end.
make_or_list([{'or',As}|Is]) ->
make_or_list(As++Is);
make_or_list([I|Is]) ->
[I|make_or_list(Is)];
make_or_list([]) -> [].
simplify_or_list([{atom,false}|T]) ->
simplify_or_list(T);
simplify_or_list([{atom,true}=True|_]) ->
[True];
simplify_or_list([H|T]) ->
[H|simplify_or_list(T)];
simplify_or_list([]) -> [].
%% Code generation for a boolean tree.
bopt_cg({'not',Arg}, Fail, Rs, Acc, St) ->
I = bopt_cg_not(Arg),
bopt_cg(I, Fail, Rs, Acc, St);
bopt_cg({'and',As}, Fail, Rs, Acc, St) ->
bopt_cg_and(As, Fail, Rs, Acc, St);
bopt_cg({'or',As}, Fail, Rs, Acc, St0) ->
{Succ,St} = new_label(St0),
bopt_cg_or(As, Succ, Fail, Rs, Acc, St);
bopt_cg({test,N,fail,As0}, Fail, Rs, Acc, St) ->
As = rename_sources(As0, Rs),
Test = {test,N,{f,Fail},As},
{[Test|Acc],St};
bopt_cg({inverted_test,N,fail,As0}, Fail, Rs, Acc, St0) ->
As = rename_sources(As0, Rs),
{Lbl,St} = new_label(St0),
{[{label,Lbl},{jump,{f,Fail}},{test,N,{f,Lbl},As}|Acc],St};
bopt_cg({prot,Pre0,Tree}, Fail, Rs0, Acc, St0) ->
Pre1 = update_fail_label(Pre0, Fail, []),
{Pre,Rs} = rename_regs(Pre1, Rs0),
bopt_cg(Tree, Fail, Rs, make_block(Pre, Acc), St0);
bopt_cg({atom,true}, _Fail, _Rs, Acc, St) ->
{Acc,St};
bopt_cg({atom,false}, Fail, _Rs, Acc, St) ->
{[{jump,{f,Fail}}|Acc],St};
bopt_cg(_, _, _, _, _) ->
throw(not_boolean_expr).
bopt_cg_not({'and',As0}) ->
As = [bopt_cg_not(A) || A <- As0],
{'or',As};
bopt_cg_not({'or',As0}) ->
As = [bopt_cg_not(A) || A <- As0],
{'and',As};
bopt_cg_not({'not',Arg}) ->
bopt_cg_not_not(Arg);
bopt_cg_not({test,Test,Fail,As}) ->
{inverted_test,Test,Fail,As};
bopt_cg_not({atom,Bool}) when is_boolean(Bool) ->
{atom,not Bool};
bopt_cg_not(_) ->
throw(not_boolean_expr).
bopt_cg_not_not({'and',As}) ->
{'and',[bopt_cg_not_not(A) || A <- As]};
bopt_cg_not_not({'or',As}) ->
{'or',[bopt_cg_not_not(A) || A <- As]};
bopt_cg_not_not({'not',Arg}) ->
bopt_cg_not(Arg);
bopt_cg_not_not(Leaf) -> Leaf.
bopt_cg_and([I|Is], Fail, Rs, Acc0, St0) ->
{Acc,St} = bopt_cg(I, Fail, Rs, Acc0, St0),
bopt_cg_and(Is, Fail, Rs, Acc, St);
bopt_cg_and([], _, _, Acc, St) -> {Acc,St}.
bopt_cg_or([I], Succ, Fail, Rs, Acc0, St0) ->
{Acc,St} = bopt_cg(I, Fail, Rs, Acc0, St0),
{[{label,Succ}|Acc],St};
bopt_cg_or([I|Is], Succ, Fail, Rs, Acc0, St0) ->
{Lbl,St1} = new_label(St0),
{Acc,St} = bopt_cg(I, Lbl, Rs, Acc0, St1),
bopt_cg_or(Is, Succ, Fail, Rs, [{label,Lbl},{jump,{f,Succ}}|Acc], St).
new_label(#st{next=LabelNum}=St) when is_integer(LabelNum) ->
{LabelNum,St#st{next=LabelNum+1}}.
free_variables(Is) ->
E = gb_sets:empty(),
free_vars_1(Is, E, E, E).
free_vars_1([{set,Ds,As,{bif,_,_}}|Is], F0, N0, A) ->
F = gb_sets:union(F0, gb_sets:difference(var_list(As), N0)),
N = gb_sets:union(N0, var_list(Ds)),
free_vars_1(Is, F, N, A);
free_vars_1([{set,Ds,As,{alloc,Regs,{gc_bif,_,_}}}|Is], F0, N0, A0) ->
A = gb_sets:union(A0, gb_sets:from_list(free_vars_regs(Regs))),
F = gb_sets:union(F0, gb_sets:difference(var_list(As), N0)),
N = gb_sets:union(N0, var_list(Ds)),
free_vars_1(Is, F, N, A);
free_vars_1([{protected,_,Pa,_}|Is], F, N, A) ->
free_vars_1(Pa++Is, F, N, A);
free_vars_1([], F0, N, A) ->
F = case gb_sets:is_empty(A) of
true ->
%% No GC BIFs.
{x,X} = gb_sets:smallest(N),
P = ordsets:from_list(free_vars_regs(X)),
ordsets:union(gb_sets:to_list(F0), P);
false ->
%% At least one GC BIF.
gb_sets:to_list(gb_sets:union(F0, gb_sets:difference(A, N)))
end,
gb_trees:from_orddict([{K,any} || K <- F]).
var_list(Is) ->
var_list_1(Is, gb_sets:empty()).
var_list_1([{Tag,_}=X|Is], D) when Tag =:= x; Tag =:= y ->
var_list_1(Is, gb_sets:add(X, D));
var_list_1([_|Is], D) ->
var_list_1(Is, D);
var_list_1([], D) -> D.
free_vars_regs(0) -> [];
free_vars_regs(X) -> [{x,X-1}|free_vars_regs(X-1)].
rename_regs(Is, Regs) ->
rename_regs(Is, Regs, []).
rename_regs([{set,[Dst0],Ss0,{alloc,_,Info}}|Is], Regs0, Acc) ->
Live = live_regs(Regs0),
Ss = rename_sources(Ss0, Regs0),
Regs = put_reg(Dst0, Regs0),
Dst = fetch_reg(Dst0, Regs),
rename_regs(Is, Regs, [{set,[Dst],Ss,{alloc,Live,Info}}|Acc]);
rename_regs([{set,[Dst0],Ss0,Info}|Is], Regs0, Acc) ->
Ss = rename_sources(Ss0, Regs0),
Regs = put_reg(Dst0, Regs0),
Dst = fetch_reg(Dst0, Regs),
rename_regs(Is, Regs, [{set,[Dst],Ss,Info}|Acc]);
rename_regs([], Regs, Acc) -> {reverse(Acc),Regs}.
rename_sources(Ss, Regs) ->
map(fun({x,_}=R) -> fetch_reg(R, Regs);
({tmp,_}=R) -> fetch_reg(R, Regs);
(E) -> E
end, Ss).
%%%
%%% Keeping track of register assignments.
%%%
init_regs(Free) ->
init_regs_1(Free, 0).
init_regs_1([{x,I}=V|T], I) ->
[{I,V}|init_regs_1(T, I+1)];
init_regs_1([{x,X}|_]=T, I) when I < X ->
[{I,reserved}|init_regs_1(T, I+1)];
init_regs_1([{y,_}|_], _) -> [];
init_regs_1([], _) -> [].
put_reg(V, Rs) -> put_reg_1(V, Rs, 0).
put_reg_1(V, [R|Rs], I) -> [R|put_reg_1(V, Rs, I+1)];
put_reg_1(V, [], I) -> [{I,V}].
fetch_reg(V, [{I,V}|_]) -> {x,I};
fetch_reg(V, [_|SRs]) -> fetch_reg(V, SRs).
live_regs([{_,reserved}|_]) ->
%% We are not sure that this register is initialized, so we must
%% abort the optimization.
throw(gc_bif_alloc_failure);
live_regs([{I,_}]) ->
I+1;
live_regs([{_,_}|Regs]) ->
live_regs(Regs);
live_regs([]) ->
0.
%%%
%%% Convert a block to Static Single Assignment (SSA) form.
%%%
-record(ssa,
{live=0, %Variable counter.
sub=gb_trees:empty(), %Substitution table.
prot=gb_sets:empty(), %Targets assigned by protecteds.
in_prot=false %Inside a protected.
}).
ssa_block(Is0) ->
{Is,_} = ssa_block_1(Is0, #ssa{}, []),
Is.
ssa_block_1([{protected,[_],Pa0,Pb}|Is], Sub0, Acc) ->
{Pa,Sub1} = ssa_block_1(Pa0, Sub0#ssa{in_prot=true}, []),
Dst = ssa_last_target(Pa),
Sub = Sub1#ssa{prot=gb_sets:insert(Dst, Sub1#ssa.prot),
in_prot=Sub0#ssa.in_prot},
ssa_block_1(Is, Sub, [{protected,[Dst],Pa,Pb}|Acc]);
ssa_block_1([{set,[Dst],As,Bif}|Is], Sub0, Acc0) ->
Sub1 = ssa_in_use_list(As, Sub0),
Sub = ssa_assign(Dst, Sub1),
Acc = [{set,[ssa_sub(Dst, Sub)],ssa_sub_list(As, Sub0),Bif}|Acc0],
ssa_block_1(Is, Sub, Acc);
ssa_block_1([], Sub, Acc) -> {reverse(Acc),Sub}.
ssa_in_use_list(As, Sub) ->
foldl(fun ssa_in_use/2, Sub, As).
ssa_in_use({x,_}=R, #ssa{sub=Sub0}=Ssa) ->
case gb_trees:is_defined(R, Sub0) of
true -> Ssa;
false ->
Sub = gb_trees:insert(R, R, Sub0),
Ssa#ssa{sub=Sub}
end;
ssa_in_use(_, Ssa) -> Ssa.
ssa_assign({x,_}=R, #ssa{sub=Sub0}=Ssa0) ->
{NewReg,Ssa} = ssa_new_reg(Ssa0),
case gb_trees:is_defined(R, Sub0) of
false ->
Sub = gb_trees:insert(R, NewReg, Sub0),
Ssa#ssa{sub=Sub};
true ->
Sub1 = gb_trees:update(R, NewReg, Sub0),
Sub = gb_trees:insert(NewReg, NewReg, Sub1),
Ssa#ssa{sub=Sub}
end.
ssa_sub_list(List, Sub) ->
[ssa_sub(E, Sub) || E <- List].
ssa_sub(R0, #ssa{sub=Sub,prot=Prot,in_prot=InProt}) ->
case gb_trees:lookup(R0, Sub) of
none -> R0;
{value,R} ->
case InProt andalso gb_sets:is_element(R, Prot) of
true ->
throw(protected_violation);
false ->
R
end
end.
ssa_new_reg(#ssa{live=Reg}=Ssa) ->
{{tmp,Reg},Ssa#ssa{live=Reg+1}}.
ssa_last_target([{set,[Dst],_,_}]) -> Dst;
ssa_last_target([_|Is]) -> ssa_last_target(Is).
%% is_killed(Register, [Instruction], FailLabel, State) -> true|false
%% Determine whether a register is killed in the instruction sequence.
%% The state is used to allow us to determine the kill state
%% across branches.
is_killed(R, Is, Label, #st{ll=Ll}) ->
beam_utils:is_killed(R, Is, Ll) andalso
beam_utils:is_killed_at(R, Label, Ll).
%% is_not_used(Register, [Instruction], FailLabel, State) -> true|false
%% Determine whether a register is never used in the instruction sequence
%% (it could still referenced by an allocate instruction, meaning that
%% it MUST be initialized).
%% The state is used to allow us to determine the usage state
%% across branches.
is_not_used(R, Is, Label, #st{ll=Ll}) ->
beam_utils:is_not_used(R, Is, Ll) andalso
beam_utils:is_not_used_at(R, Label, Ll).
%% initialized_regs([Instruction]) -> [Register])
%% Given a REVERSED instruction sequence, return a list of the registers
%% that are guaranteed to be initialized (not contain garbage).
initialized_regs(Is) ->
initialized_regs(Is, ordsets:new()).
initialized_regs([{set,Dst,_Src,{alloc,Live,_}}|_], Regs0) ->
Regs = add_init_regs(free_vars_regs(Live), Regs0),
add_init_regs(Dst, Regs);
initialized_regs([{set,Dst,Src,_}|Is], Regs) ->
initialized_regs(Is, add_init_regs(Dst, add_init_regs(Src, Regs)));
initialized_regs([{test,_,_,Src}|Is], Regs) ->
initialized_regs(Is, add_init_regs(Src, Regs));
initialized_regs([{block,Bl}|Is], Regs) ->
initialized_regs(reverse(Bl, Is), Regs);
initialized_regs([{bs_context_to_binary,Src}|Is], Regs) ->
initialized_regs(Is, add_init_regs([Src], Regs));
initialized_regs([{label,_},{func_info,_,_,Arity}|_], Regs) ->
InitRegs = free_vars_regs(Arity),
add_init_regs(InitRegs, Regs);
initialized_regs([_|_], Regs) -> Regs.
add_init_regs([{x,_}=X|T], Regs) ->
add_init_regs(T, ordsets:add_element(X, Regs));
add_init_regs([_|T], Regs) ->
add_init_regs(T, Regs);
add_init_regs([], Regs) -> Regs.
