%%
%% %CopyrightBegin%
%%
%% Copyright Ericsson AB 1999-2012. All Rights Reserved.
%%
%% The contents of this file are subject to the Erlang Public License,
%% Version 1.1, (the "License"); you may not use this file except in
%% compliance with the License. You should have received a copy of the
%% Erlang Public License along with this software. If not, it can be
%% retrieved online at http://www.erlang.org/.
%%
%% Software distributed under the License is distributed on an "AS IS"
%% basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
%% the License for the specific language governing rights and limitations
%% under the License.
%%
%% %CopyrightEnd%
%%
%% Purpose : Convert annotated kernel expressions to annotated beam format.
%% This module creates beam format annotated with variable lifetime
%% information. Each thing is given an index and for each variable we
%% store the first and last index for its occurrence. The variable
%% database, VDB, attached to each thing is only relevant internally
%% for that thing.
%%
%% For nested things like matches the numbering continues locally and
%% the VDB for that thing refers to the variable usage within that
%% thing. Variables which live through a such a thing are internally
%% given a very large last index. Internally the indexes continue
%% after the index of that thing. This creates no problems as the
%% internal variable info never escapes and externally we only see
%% variable which are alive both before or after.
%%
%% This means that variables never "escape" from a thing and the only
%% way to get values from a thing is to "return" them, with 'break' or
%% 'return'. Externally these values become the return values of the
%% thing. This is no real limitation as most nested things have
%% multiple threads so working out a common best variable usage is
%% difficult.
-module(v3_life).
-export([module/2]).
-export([vdb_find/2]).
-import(lists, [member/2,map/2,foldl/3,reverse/1,sort/1]).
-import(ordsets, [add_element/2,intersection/2,union/2]).
-include("v3_kernel.hrl").
-include("v3_life.hrl").
%% These are not defined in v3_kernel.hrl.
get_kanno(Kthing) -> element(2, Kthing).
%%set_kanno(Kthing, Anno) -> setelement(2, Kthing, Anno).
module(#k_mdef{name=M,exports=Es,attributes=As,body=Fs0}, _Opts) ->
Fs1 = functions(Fs0, []),
{ok,{M,Es,As,Fs1}}.
functions([F|Fs], Acc) ->
functions(Fs, [function(F)|Acc]);
functions([], Acc) -> reverse(Acc).
%% function(Kfunc) -> Func.
function(#k_fdef{anno=#k{a=Anno},func=F,arity=Ar,vars=Vs,body=Kb}) ->
try
As = var_list(Vs),
Vdb0 = foldl(fun ({var,N}, Vdb) -> new_var(N, 0, Vdb) end, [], As),
%% Force a top-level match!
B0 = case Kb of
#k_match{} -> Kb;
_ ->
Ka = get_kanno(Kb),
#k_match{anno=#k{us=Ka#k.us,ns=[],a=Ka#k.a},
vars=Vs,body=Kb,ret=[]}
end,
put(guard_refc, 0),
{B1,_,Vdb1} = body(B0, 1, Vdb0),
erase(guard_refc),
{function,F,Ar,As,B1,Vdb1,Anno}
catch
Class:Error ->
Stack = erlang:get_stacktrace(),
io:fwrite("Function: ~w/~w\n", [F,Ar]),
erlang:raise(Class, Error, Stack)
end.
%% body(Kbody, I, Vdb) -> {[Expr],MaxI,Vdb}.
%% Handle a body.
body(#k_seq{arg=Ke,body=Kb}, I, Vdb0) ->
%%ok = io:fwrite("life ~w:~p~n", [?LINE,{Ke,I,Vdb0}]),
A = get_kanno(Ke),
Vdb1 = use_vars(A#k.us, I, new_vars(A#k.ns, I, Vdb0)),
{Es,MaxI,Vdb2} = body(Kb, I+1, Vdb1),
E = expr(Ke, I, Vdb2),
{[E|Es],MaxI,Vdb2};
body(Ke, I, Vdb0) ->
%%ok = io:fwrite("life ~w:~p~n", [?LINE,{Ke,I,Vdb0}]),
A = get_kanno(Ke),
Vdb1 = use_vars(A#k.us, I, new_vars(A#k.ns, I, Vdb0)),
E = expr(Ke, I, Vdb1),
{[E],I,Vdb1}.
%% guard(Kguard, I, Vdb) -> Guard.
guard(#k_try{anno=A,arg=Ts,vars=[#k_var{name=X}],body=#k_var{name=X},
handler=#k_atom{val=false},ret=Rs}, I, Vdb) ->
%% Lock variables that are alive before try and used afterwards.
%% Don't lock variables that are only used inside the try expression.
Pdb0 = vdb_sub(I, I+1, Vdb),
{T,MaxI,Pdb1} = body(Ts, I+1, Pdb0),
Pdb2 = use_vars(A#k.ns, MaxI+1, Pdb1), %Save "return" values
#l{ke={protected,T,var_list(Rs)},i=I,a=A#k.a,vdb=Pdb2}.
%% expr(Kexpr, I, Vdb) -> Expr.
expr(#k_test{anno=A,op=Op,args=As}, I, _Vdb) ->
#l{ke={test,test_op(Op),atomic_list(As)},i=I,a=A#k.a};
expr(#k_call{anno=A,op=Op,args=As,ret=Rs}, I, _Vdb) ->
#l{ke={call,call_op(Op),atomic_list(As),var_list(Rs)},i=I,a=A#k.a};
expr(#k_enter{anno=A,op=Op,args=As}, I, _Vdb) ->
#l{ke={enter,call_op(Op),atomic_list(As)},i=I,a=A#k.a};
expr(#k_bif{anno=A,op=Op,args=As,ret=Rs}, I, _Vdb) ->
Bif = k_bif(A, Op, As, Rs),
#l{ke=Bif,i=I,a=A#k.a};
expr(#k_match{anno=A,body=Kb,ret=Rs}, I, Vdb) ->
%% Work out imported variables which need to be locked.
Mdb = vdb_sub(I, I+1, Vdb),
M = match(Kb, A#k.us, I+1, [], Mdb),
#l{ke={match,M,var_list(Rs)},i=I,vdb=use_vars(A#k.us, I+1, Mdb),a=A#k.a};
expr(#k_guard_match{anno=A,body=Kb,ret=Rs}, I, Vdb) ->
%% Work out imported variables which need to be locked.
Mdb = vdb_sub(I, I+1, Vdb),
M = match(Kb, A#k.us, I+1, [], Mdb),
#l{ke={guard_match,M,var_list(Rs)},i=I,vdb=use_vars(A#k.us, I+1, Mdb),a=A#k.a};
expr(#k_try{}=Try, I, Vdb) ->
case is_in_guard() of
false -> body_try(Try, I, Vdb);
true -> guard(Try, I, Vdb)
end;
expr(#k_try_enter{anno=A,arg=Ka,vars=Vs,body=Kb,evars=Evs,handler=Kh}, I, Vdb) ->
%% Lock variables that are alive before the catch and used afterwards.
%% Don't lock variables that are only used inside the try.
Tdb0 = vdb_sub(I, I+1, Vdb),
%% This is the tricky bit. Lock variables in Arg that are used in
%% the body and handler. Add try tag 'variable'.
Ab = get_kanno(Kb),
Ah = get_kanno(Kh),
Tdb1 = use_vars(Ab#k.us, I+3, use_vars(Ah#k.us, I+3, Tdb0)),
Tdb2 = vdb_sub(I, I+2, Tdb1),
Vnames = fun (Kvar) -> Kvar#k_var.name end, %Get the variable names
{Aes,_,Adb} = body(Ka, I+2, add_var({catch_tag,I+1}, I+1, 1000000, Tdb2)),
{Bes,_,Bdb} = body(Kb, I+4, new_vars(map(Vnames, Vs), I+3, Tdb2)),
{Hes,_,Hdb} = body(Kh, I+4, new_vars(map(Vnames, Evs), I+3, Tdb2)),
#l{ke={try_enter,#l{ke={block,Aes},i=I+1,vdb=Adb,a=[]},
var_list(Vs),#l{ke={block,Bes},i=I+3,vdb=Bdb,a=[]},
var_list(Evs),#l{ke={block,Hes},i=I+3,vdb=Hdb,a=[]}},
i=I,vdb=Tdb1,a=A#k.a};
expr(#k_catch{anno=A,body=Kb,ret=[R]}, I, Vdb) ->
%% Lock variables that are alive before the catch and used afterwards.
%% Don't lock variables that are only used inside the catch.
%% Add catch tag 'variable'.
Cdb0 = vdb_sub(I, I+1, Vdb),
{Es,_,Cdb1} = body(Kb, I+1, add_var({catch_tag,I}, I, locked, Cdb0)),
#l{ke={'catch',Es,variable(R)},i=I,vdb=Cdb1,a=A#k.a};
expr(#k_receive{anno=A,var=V,body=Kb,timeout=T,action=Ka,ret=Rs}, I, Vdb) ->
%% Work out imported variables which need to be locked.
Rdb = vdb_sub(I, I+1, Vdb),
M = match(Kb, add_element(V#k_var.name, A#k.us), I+1, [],
new_var(V#k_var.name, I, Rdb)),
{Tes,_,Adb} = body(Ka, I+1, Rdb),
#l{ke={receive_loop,atomic(T),variable(V),M,
#l{ke=Tes,i=I+1,vdb=Adb,a=[]},var_list(Rs)},
i=I,vdb=use_vars(A#k.us, I+1, Vdb),a=A#k.a};
expr(#k_receive_accept{anno=A}, I, _Vdb) ->
#l{ke=receive_accept,i=I,a=A#k.a};
expr(#k_receive_next{anno=A}, I, _Vdb) ->
#l{ke=receive_next,i=I,a=A#k.a};
expr(#k_put{anno=A,arg=Arg,ret=Rs}, I, _Vdb) ->
#l{ke={set,var_list(Rs),literal(Arg, [])},i=I,a=A#k.a};
expr(#k_break{anno=A,args=As}, I, _Vdb) ->
#l{ke={break,atomic_list(As)},i=I,a=A#k.a};
expr(#k_guard_break{anno=A,args=As}, I, Vdb) ->
Locked = [V || {V,_,_} <- Vdb],
#l{ke={guard_break,atomic_list(As),Locked},i=I,a=A#k.a};
expr(#k_return{anno=A,args=As}, I, _Vdb) ->
#l{ke={return,atomic_list(As)},i=I,a=A#k.a}.
body_try(#k_try{anno=A,arg=Ka,vars=Vs,body=Kb,evars=Evs,handler=Kh,ret=Rs},
I, Vdb) ->
%% Lock variables that are alive before the catch and used afterwards.
%% Don't lock variables that are only used inside the try.
Tdb0 = vdb_sub(I, I+1, Vdb),
%% This is the tricky bit. Lock variables in Arg that are used in
%% the body and handler. Add try tag 'variable'.
Ab = get_kanno(Kb),
Ah = get_kanno(Kh),
Tdb1 = use_vars(Ab#k.us, I+3, use_vars(Ah#k.us, I+3, Tdb0)),
Tdb2 = vdb_sub(I, I+2, Tdb1),
Vnames = fun (Kvar) -> Kvar#k_var.name end, %Get the variable names
{Aes,_,Adb} = body(Ka, I+2, add_var({catch_tag,I+1}, I+1, locked, Tdb2)),
{Bes,_,Bdb} = body(Kb, I+4, new_vars(map(Vnames, Vs), I+3, Tdb2)),
{Hes,_,Hdb} = body(Kh, I+4, new_vars(map(Vnames, Evs), I+3, Tdb2)),
#l{ke={'try',#l{ke={block,Aes},i=I+1,vdb=Adb,a=[]},
var_list(Vs),#l{ke={block,Bes},i=I+3,vdb=Bdb,a=[]},
var_list(Evs),#l{ke={block,Hes},i=I+3,vdb=Hdb,a=[]},
var_list(Rs)},
i=I,vdb=Tdb1,a=A#k.a}.
%% call_op(Op) -> Op.
%% bif_op(Op) -> Op.
%% test_op(Op) -> Op.
%% Do any necessary name translations here to munge into beam format.
call_op(#k_local{name=N}) -> N;
call_op(#k_remote{mod=M,name=N}) -> {remote,atomic(M),atomic(N)};
call_op(Other) -> variable(Other).
bif_op(#k_remote{mod=#k_atom{val=erlang},name=#k_atom{val=N}}) -> N;
bif_op(#k_internal{name=N}) -> N.
test_op(#k_remote{mod=#k_atom{val=erlang},name=#k_atom{val=N}}) -> N.
%% k_bif(Anno, Op, [Arg], [Ret], Vdb) -> Expr.
%% Build bifs, do special handling of internal some calls.
k_bif(_A, #k_internal{name=dsetelement,arity=3}, As, []) ->
{bif,dsetelement,atomic_list(As),[]};
k_bif(_A, #k_internal{name=bs_context_to_binary=Op,arity=1}, As, []) ->
{bif,Op,atomic_list(As),[]};
k_bif(_A, #k_internal{name=bs_init_writable=Op,arity=1}, As, Rs) ->
{bif,Op,atomic_list(As),var_list(Rs)};
k_bif(_A, #k_internal{name=make_fun},
[#k_atom{val=Fun},#k_int{val=Arity},
#k_int{val=Index},#k_int{val=Uniq}|Free],
Rs) ->
{bif,{make_fun,Fun,Arity,Index,Uniq},var_list(Free),var_list(Rs)};
k_bif(_A, Op, As, Rs) ->
%% The general case.
Name = bif_op(Op),
Ar = length(As),
case is_gc_bif(Name, Ar) of
false ->
{bif,Name,atomic_list(As),var_list(Rs)};
true ->
{gc_bif,Name,atomic_list(As),var_list(Rs)}
end.
%% match(Kexpr, [LockVar], I, Vdb) -> Expr.
%% Convert match tree to old format.
match(#k_alt{anno=A,first=Kf,then=Kt}, Ls, I, Ctxt, Vdb0) ->
Vdb1 = use_vars(union(A#k.us, Ls), I, Vdb0),
F = match(Kf, Ls, I+1, Ctxt, Vdb1),
T = match(Kt, Ls, I+1, Ctxt, Vdb1),
#l{ke={alt,F,T},i=I,vdb=Vdb1,a=A#k.a};
match(#k_select{anno=A,var=V,types=Kts}, Ls0, I, Ctxt, Vdb0) ->
Vanno = get_kanno(V),
Ls1 = case member(no_usage, Vanno) of
false -> add_element(V#k_var.name, Ls0);
true -> Ls0
end,
Anno = case member(reuse_for_context, Vanno) of
true -> [reuse_for_context|A#k.a];
false -> A#k.a
end,
Vdb1 = use_vars(union(A#k.us, Ls1), I, Vdb0),
Ts = [type_clause(Tc, Ls1, I+1, Ctxt, Vdb1) || Tc <- Kts],
#l{ke={select,literal2(V, Ctxt),Ts},i=I,vdb=Vdb1,a=Anno};
match(#k_guard{anno=A,clauses=Kcs}, Ls, I, Ctxt, Vdb0) ->
Vdb1 = use_vars(union(A#k.us, Ls), I, Vdb0),
Cs = [guard_clause(G, Ls, I+1, Ctxt, Vdb1) || G <- Kcs],
#l{ke={guard,Cs},i=I,vdb=Vdb1,a=A#k.a};
match(Other, Ls, I, _Ctxt, Vdb0) ->
Vdb1 = use_vars(Ls, I, Vdb0),
{B,_,Vdb2} = body(Other, I+1, Vdb1),
#l{ke={block,B},i=I,vdb=Vdb2,a=[]}.
type_clause(#k_type_clause{anno=A,type=T,values=Kvs}, Ls, I, Ctxt, Vdb0) ->
%%ok = io:format("life ~w: ~p~n", [?LINE,{T,Kvs}]),
Vdb1 = use_vars(union(A#k.us, Ls), I+1, Vdb0),
Vs = [val_clause(Vc, Ls, I+1, Ctxt, Vdb1) || Vc <- Kvs],
#l{ke={type_clause,type(T),Vs},i=I,vdb=Vdb1,a=A#k.a}.
val_clause(#k_val_clause{anno=A,val=V,body=Kb}, Ls0, I, Ctxt0, Vdb0) ->
New = (get_kanno(V))#k.ns,
Bus = (get_kanno(Kb))#k.us,
%%ok = io:format("Ls0 = ~p, Used=~p\n New=~p, Bus=~p\n", [Ls0,Used,New,Bus]),
Ls1 = union(intersection(New, Bus), Ls0), %Lock for safety
Vdb1 = use_vars(union(A#k.us, Ls1), I+1, new_vars(New, I, Vdb0)),
Ctxt = case V of
#k_binary{segs=#k_var{name=C0}} -> C0;
_ -> Ctxt0
end,
B = match(Kb, Ls1, I+1, Ctxt, Vdb1),
#l{ke={val_clause,literal2(V, Ctxt),B},i=I,vdb=use_vars(Bus, I+1, Vdb1),a=A#k.a}.
guard_clause(#k_guard_clause{anno=A,guard=Kg,body=Kb}, Ls, I, Ctxt, Vdb0) ->
Vdb1 = use_vars(union(A#k.us, Ls), I+2, Vdb0),
Gdb = vdb_sub(I+1, I+2, Vdb1),
OldRefc = put(guard_refc, get(guard_refc)+1),
G = guard(Kg, I+1, Gdb),
put(guard_refc, OldRefc),
B = match(Kb, Ls, I+2, Ctxt, Vdb1),
#l{ke={guard_clause,G,B},
i=I,vdb=use_vars((get_kanno(Kg))#k.us, I+2, Vdb1),
a=A#k.a}.
%% type(Ktype) -> Type.
type(k_literal) -> literal;
type(k_int) -> integer;
%%type(k_char) -> integer; %Hhhmmm???
type(k_float) -> float;
type(k_atom) -> atom;
type(k_nil) -> nil;
type(k_cons) -> cons;
type(k_tuple) -> tuple;
type(k_binary) -> binary;
type(k_bin_seg) -> bin_seg;
type(k_bin_int) -> bin_int;
type(k_bin_end) -> bin_end;
type(k_map) -> map.
%% variable(Klit) -> Lit.
%% var_list([Klit]) -> [Lit].
variable(#k_var{name=N}) -> {var,N}.
var_list(Ks) -> [variable(K) || K <- Ks].
%% atomic(Klit) -> Lit.
%% atomic_list([Klit]) -> [Lit].
atomic(#k_literal{val=V}) -> {literal,V};
atomic(#k_var{name=N}) -> {var,N};
atomic(#k_int{val=I}) -> {integer,I};
atomic(#k_float{val=F}) -> {float,F};
atomic(#k_atom{val=N}) -> {atom,N};
%%atomic(#k_char{val=C}) -> {char,C};
atomic(#k_nil{}) -> nil.
atomic_list(Ks) -> [atomic(K) || K <- Ks].
%% literal(Klit) -> Lit.
%% literal_list([Klit]) -> [Lit].
literal(#k_var{name=N}, _) -> {var,N};
literal(#k_int{val=I}, _) -> {integer,I};
literal(#k_float{val=F}, _) -> {float,F};
literal(#k_atom{val=N}, _) -> {atom,N};
%%literal(#k_char{val=C}, _) -> {char,C};
literal(#k_nil{}, _) -> nil;
literal(#k_cons{hd=H,tl=T}, Ctxt) ->
{cons,[literal(H, Ctxt),literal(T, Ctxt)]};
literal(#k_binary{segs=V}, Ctxt) ->
{binary,literal(V, Ctxt)};
literal(#k_bin_seg{size=S,unit=U,type=T,flags=Fs,seg=Seg,next=N}, Ctxt) ->
{bin_seg,Ctxt,literal(S, Ctxt),U,T,Fs,
[literal(Seg, Ctxt),literal(N, Ctxt)]};
literal(#k_bin_end{}, Ctxt) ->
{bin_end,Ctxt};
literal(#k_tuple{es=Es}, Ctxt) ->
{tuple,literal_list(Es, Ctxt)};
literal(#k_map{op=Op,var=Var,es=Es}, Ctxt) ->
{map,Op,literal(Var, Ctxt),literal_list(Es, Ctxt)};
literal(#k_map_pair{key=K,val=V}, Ctxt) ->
{map_pair,literal(K, Ctxt),literal(V, Ctxt)};
literal(#k_literal{val=V}, _Ctxt) ->
{literal,V}.
literal_list(Ks, Ctxt) ->
[literal(K, Ctxt) || K <- Ks].
literal2(#k_var{name=N}, _) -> {var,N};
literal2(#k_literal{val=I}, _) -> {literal,I};
literal2(#k_int{val=I}, _) -> {integer,I};
literal2(#k_float{val=F}, _) -> {float,F};
literal2(#k_atom{val=N}, _) -> {atom,N};
%%literal2(#k_char{val=C}, _) -> {char,C};
literal2(#k_nil{}, _) -> nil;
literal2(#k_cons{hd=H,tl=T}, Ctxt) ->
{cons,[literal2(H, Ctxt),literal2(T, Ctxt)]};
literal2(#k_binary{segs=V}, Ctxt) ->
{binary,literal2(V, Ctxt)};
literal2(#k_bin_seg{size=S,unit=U,type=T,flags=Fs,seg=Seg,next=[]}, Ctxt) ->
{bin_seg,Ctxt,literal2(S, Ctxt),U,T,Fs,[literal2(Seg, Ctxt)]};
literal2(#k_bin_seg{size=S,unit=U,type=T,flags=Fs,seg=Seg,next=N}, Ctxt) ->
{bin_seg,Ctxt,literal2(S, Ctxt),U,T,Fs,
[literal2(Seg, Ctxt),literal2(N, Ctxt)]};
literal2(#k_bin_int{size=S,unit=U,flags=Fs,val=Int,next=N}, Ctxt) ->
{bin_int,Ctxt,literal2(S, Ctxt),U,Fs,Int,
[literal2(N, Ctxt)]};
literal2(#k_bin_end{}, Ctxt) ->
{bin_end,Ctxt};
literal2(#k_tuple{es=Es}, Ctxt) ->
{tuple,literal_list2(Es, Ctxt)};
literal2(#k_map{op=Op,es=Es}, Ctxt) ->
{map,Op,literal_list2(Es, Ctxt)};
literal2(#k_map_pair{key=K,val=V}, Ctxt) ->
{map_pair,literal2(K, Ctxt),literal2(V, Ctxt)}.
literal_list2(Ks, Ctxt) ->
[literal2(K, Ctxt) || K <- Ks].
%% literal_bin(#k_bin_seg{size=S,unit=U,type=T,flags=Fs,seg=Seg,next=N}) ->
%% {bin_seg,literal(S),U,T,Fs,[literal(Seg),literal(N)]}
%% is_gc_bif(Name, Arity) -> true|false
%% Determines whether the BIF Name/Arity might do a GC.
is_gc_bif(hd, 1) -> false;
is_gc_bif(tl, 1) -> false;
is_gc_bif(self, 0) -> false;
is_gc_bif(node, 0) -> false;
is_gc_bif(node, 1) -> false;
is_gc_bif(element, 2) -> false;
is_gc_bif(get, 1) -> false;
is_gc_bif(raise, 2) -> false;
is_gc_bif(tuple_size, 1) -> false;
is_gc_bif(Bif, Arity) ->
not (erl_internal:bool_op(Bif, Arity) orelse
erl_internal:new_type_test(Bif, Arity) orelse
erl_internal:comp_op(Bif, Arity)).
%% new_var(VarName, I, Vdb) -> Vdb.
%% new_vars([VarName], I, Vdb) -> Vdb.
%% use_var(VarName, I, Vdb) -> Vdb.
%% use_vars([VarName], I, Vdb) -> Vdb.
%% add_var(VarName, F, L, Vdb) -> Vdb.
new_var(V, I, Vdb) ->
vdb_store_new(V, I, I, Vdb).
new_vars(Vs, I, Vdb0) ->
foldl(fun (V, Vdb) -> new_var(V, I, Vdb) end, Vdb0, Vs).
use_var(V, I, Vdb) ->
case vdb_find(V, Vdb) of
{V,F,L} when I > L -> vdb_update(V, F, I, Vdb);
{V,_,_} -> Vdb;
error -> vdb_store_new(V, I, I, Vdb)
end.
use_vars([], _, Vdb) -> Vdb;
use_vars([V], I, Vdb) -> use_var(V, I, Vdb);
use_vars(Vs, I, Vdb) ->
Res = use_vars_1(sort(Vs), Vdb, I),
%% The following line can be used as an assertion.
%% Res = foldl(fun (V, Vdb) -> use_var(V, I, Vdb) end, Vdb, Vs),
Res.
%% Measurements show that it is worthwhile having this special
%% function that updates/inserts several variables at once.
use_vars_1([V|_]=Vs, [{V1,_,_}=Vd|Vdb], I) when V > V1 ->
[Vd|use_vars_1(Vs, Vdb, I)];
use_vars_1([V|Vs], [{V1,_,_}|_]=Vdb, I) when V < V1 ->
%% New variable.
[{V,I,I}|use_vars_1(Vs, Vdb, I)];
use_vars_1([V|Vs], [{_,F,L}=Vd|Vdb], I) ->
%% Existing variable.
if
I > L ->[{V,F,I}|use_vars_1(Vs, Vdb, I)];
true -> [Vd|use_vars_1(Vs, Vdb, I)]
end;
use_vars_1([V|Vs], [], I) ->
%% New variable.
[{V,I,I}|use_vars_1(Vs, [], I)];
use_vars_1([], Vdb, _) -> Vdb.
add_var(V, F, L, Vdb) ->
vdb_store_new(V, F, L, Vdb).
vdb_find(V, Vdb) ->
%% Performance note: Profiling shows that this function accounts for
%% a lot of the execution time when huge constant terms are built.
%% Using the BIF lists:keyfind/3 is a lot faster than the
%% original Erlang version.
case lists:keyfind(V, 1, Vdb) of
false -> error;
Vd -> Vd
end.
%vdb_find(V, [{V1,F,L}=Vd|Vdb]) when V < V1 -> error;
%vdb_find(V, [{V1,F,L}=Vd|Vdb]) when V == V1 -> Vd;
%vdb_find(V, [{V1,F,L}=Vd|Vdb]) when V > V1 -> vdb_find(V, Vdb);
%vdb_find(V, []) -> error.
vdb_update(V, F, L, [{V1,_,_}=Vd|Vdb]) when V > V1 ->
[Vd|vdb_update(V, F, L, Vdb)];
vdb_update(V, F, L, [{V1,_,_}|Vdb]) when V == V1 ->
[{V,F,L}|Vdb].
vdb_store_new(V, F, L, [{V1,_,_}=Vd|Vdb]) when V > V1 ->
[Vd|vdb_store_new(V, F, L, Vdb)];
vdb_store_new(V, F, L, [{V1,_,_}|_]=Vdb) when V < V1 -> [{V,F,L}|Vdb];
vdb_store_new(V, F, L, []) -> [{V,F,L}].
%% vdb_sub(Min, Max, Vdb) -> Vdb.
%% Extract variables which are used before and after Min. Lock
%% variables alive after Max.
vdb_sub(Min, Max, Vdb) ->
[ if L >= Max -> {V,F,locked};
true -> Vd
end || {V,F,L}=Vd <- Vdb, F < Min, L >= Min ].
%% is_in_guard() -> true|false.
is_in_guard() ->
get(guard_refc) > 0.
