%%
%% %CopyrightBegin%
%%
%% Copyright Ericsson AB 1999-2013. 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 : Constant folding optimisation for Core
%% Propagate atomic values and fold in values of safe calls to
%% constant arguments. Also detect and remove literals which are
%% ignored in a 'seq'. Could handle lets better by chasing down
%% complex 'arg' expressions and finding values.
%%
%% Try to optimise case expressions by removing unmatchable or
%% unreachable clauses. Also change explicit tuple arg into multiple
%% values and extend clause patterns. We must be careful here not to
%% generate cases which we know to be safe but later stages will not
%% recognise as such, e.g. the following is NOT acceptable:
%%
%% case 'b' of
%% <'b'> -> ...
%% end
%%
%% Variable folding is complicated by variable shadowing, for example
%% in:
%% 'foo'/1 =
%% fun (X) ->
%% let <A> = X
%% in let <X> = Y
%% in ... <use A>
%% If we were to simply substitute X for A then we would be using the
%% wrong X. Our solution is to rename variables that are the values
%% of substitutions. We could rename all shadowing variables but do
%% the minimum. We would then get:
%% 'foo'/1 =
%% fun (X) ->
%% let <A> = X
%% in let <X1> = Y
%% in ... <use A>
%% which is optimised to:
%% 'foo'/1 =
%% fun (X) ->
%% let <X1> = Y
%% in ... <use X>
%%
%% This is done by carefully shadowing variables and substituting
%% values. See details when defining functions.
%%
%% It would be possible to extend to replace repeated evaluation of
%% "simple" expressions by the value (variable) of the first call.
%% For example, after a "let Z = X+1" then X+1 would be replaced by Z
%% where X is valid. The Sub uses the full Core expression as key.
%% It would complicate handling of patterns as we would have to remove
%% all values where the key contains pattern variables.
-module(sys_core_fold).
-export([module/2,format_error/1]).
-import(lists, [map/2,foldl/3,foldr/3,mapfoldl/3,all/2,any/2,
reverse/1,reverse/2,member/2,nth/2,flatten/1,
unzip/1,keyfind/3]).
-import(cerl, [ann_c_cons/3,ann_c_map/3,ann_c_tuple/2]).
-include("core_parse.hrl").
%%-define(DEBUG, 1).
-ifdef(DEBUG).
-define(ASSERT(E),
case E of
true -> ok;
false ->
io:format("~p, line ~p: assertion failed\n", [?MODULE,?LINE]),
exit(assertion_failed)
end).
-else.
-define(ASSERT(E), ignore).
-endif.
%% Variable value info.
-record(sub, {v=[], %Variable substitutions
s=cerl_sets:new() :: cerl_sets:set(), %Variables in scope
t=#{} :: map(), %Types
in_guard=false}). %In guard or not.
-type type_info() :: cerl:cerl() | 'bool' | 'integer'.
-type yes_no_maybe() :: 'yes' | 'no' | 'maybe'.
-type sub() :: #sub{}.
-spec module(cerl:c_module(), [compile:option()]) ->
{'ok', cerl:c_module(), [_]}.
module(#c_module{defs=Ds0}=Mod, Opts) ->
put(bin_opt_info, member(bin_opt_info, Opts)),
put(no_inline_list_funcs, not member(inline_list_funcs, Opts)),
case get(new_var_num) of
undefined -> put(new_var_num, 0);
_ -> ok
end,
init_warnings(),
Ds1 = [function_1(D) || D <- Ds0],
erase(no_inline_list_funcs),
erase(bin_opt_info),
{ok,Mod#c_module{defs=Ds1},get_warnings()}.
function_1({#c_var{name={F,Arity}}=Name,B0}) ->
try
B = expr(B0, value, sub_new()), %This must be a fun!
{Name,B}
catch
Class:Error ->
Stack = erlang:get_stacktrace(),
io:fwrite("Function: ~w/~w\n", [F,Arity]),
erlang:raise(Class, Error, Stack)
end.
%% body(Expr, Sub) -> Expr.
%% body(Expr, Context, Sub) -> Expr.
%% No special handling of anything except values.
body(Body, Sub) ->
body(Body, value, Sub).
body(#c_values{anno=A,es=Es0}, Ctxt, Sub) ->
Es1 = expr_list(Es0, Ctxt, Sub),
case Ctxt of
value ->
#c_values{anno=A,es=Es1};
effect ->
make_effect_seq(Es1, Sub)
end;
body(E, Ctxt, Sub) ->
?ASSERT(verify_scope(E, Sub)),
expr(E, Ctxt, Sub).
%% guard(Expr, Sub) -> Expr.
%% Do guard expression. We optimize it in the same way as
%% expressions in function bodies.
guard(Expr, Sub) ->
?ASSERT(verify_scope(Expr, Sub)),
expr(Expr, value, Sub#sub{in_guard=true}).
%% opt_guard_try(Expr) -> Expr.
%%
opt_guard_try(#c_seq{arg=Arg,body=Body0}=Seq) ->
Body = opt_guard_try(Body0),
case {Arg,Body} of
{#c_call{module=#c_literal{val=Mod},
name=#c_literal{val=Name},
args=Args},#c_literal{val=false}} ->
%% We have sequence consisting of a call (evaluated
%% for a possible exception and/or side effect only),
%% followed by 'false'.
%% Since the sequence is inside a try block that will
%% default to 'false' if any exception occurs, not
%% evalutating the call will not change the behaviour
%% provided that the call has no side effects.
case erl_bifs:is_pure(Mod, Name, length(Args)) of
false ->
%% Not a pure BIF (meaning that this is not
%% a guard and that we must keep the call).
Seq#c_seq{body=Body};
true ->
%% The BIF has no side effects, so it can
%% be safely removed.
Body
end;
{_,_} ->
Seq#c_seq{body=Body}
end;
opt_guard_try(#c_case{clauses=Cs}=Term) ->
Term#c_case{clauses=opt_guard_try_list(Cs)};
opt_guard_try(#c_clause{body=B0}=Term) ->
Term#c_clause{body=opt_guard_try(B0)};
opt_guard_try(#c_let{arg=Arg,body=B0}=Term) ->
case opt_guard_try(B0) of
#c_literal{}=B ->
opt_guard_try(#c_seq{arg=Arg,body=B});
B ->
Term#c_let{body=B}
end;
opt_guard_try(Term) -> Term.
opt_guard_try_list([C|Cs]) ->
[opt_guard_try(C)|opt_guard_try_list(Cs)];
opt_guard_try_list([]) -> [].
%% expr(Expr, Sub) -> Expr.
%% expr(Expr, Context, Sub) -> Expr.
expr(Expr, Sub) ->
expr(Expr, value, Sub).
expr(#c_var{}=V, Ctxt, Sub) ->
%% Return void() in effect context to potentially shorten the life time
%% of the variable and potentially generate better code
%% (for instance, if the variable no longer needs to survive a function
%% call, there will be no need to save it in the stack frame).
case Ctxt of
effect -> void();
value -> sub_get_var(V, Sub)
end;
expr(#c_literal{val=Val}=L, Ctxt, _Sub) ->
case Ctxt of
effect ->
case Val of
[] ->
%% Keep as [] - might give slightly better code.
L;
_ when is_atom(Val) ->
%% For cleanliness replace with void().
void();
_ ->
%% Warn and replace with void().
add_warning(L, useless_building),
void()
end;
value -> L
end;
expr(#c_cons{anno=Anno,hd=H0,tl=T0}=Cons, Ctxt, Sub) ->
H1 = expr(H0, Ctxt, Sub),
T1 = expr(T0, Ctxt, Sub),
case Ctxt of
effect ->
add_warning(Cons, useless_building),
expr(make_effect_seq([H1,T1], Sub), Ctxt, Sub);
value ->
ann_c_cons(Anno, H1, T1)
end;
expr(#c_tuple{anno=Anno,es=Es0}=Tuple, Ctxt, Sub) ->
Es = expr_list(Es0, Ctxt, Sub),
case Ctxt of
effect ->
add_warning(Tuple, useless_building),
expr(make_effect_seq(Es, Sub), Ctxt, Sub);
value ->
ann_c_tuple(Anno, Es)
end;
expr(#c_map{anno=Anno,arg=V0,es=Es0}=Map, Ctxt, Sub) ->
Es = pair_list(Es0, Ctxt, Sub),
case Ctxt of
effect ->
add_warning(Map, useless_building),
expr(make_effect_seq(Es, Sub), Ctxt, Sub);
value ->
V = expr(V0, Ctxt, Sub),
ann_c_map(Anno,V,Es)
end;
expr(#c_binary{segments=Ss}=Bin0, Ctxt, Sub) ->
%% Warn for useless building, but always build the binary
%% anyway to preserve a possible exception.
case Ctxt of
effect -> add_warning(Bin0, useless_building);
value -> ok
end,
Bin1 = Bin0#c_binary{segments=bitstr_list(Ss, Sub)},
Bin = bin_un_utf(Bin1),
eval_binary(Bin);
expr(#c_fun{}=Fun, effect, _) ->
%% A fun is created, but not used. Warn, and replace with the void value.
add_warning(Fun, useless_building),
void();
expr(#c_fun{vars=Vs0,body=B0}=Fun, Ctxt0, Sub0) ->
{Vs1,Sub1} = pattern_list(Vs0, Sub0),
Ctxt = case Ctxt0 of
{letrec,Ctxt1} -> Ctxt1;
value -> value
end,
B1 = body(B0, Ctxt, Sub1),
Fun#c_fun{vars=Vs1,body=B1};
expr(#c_seq{arg=Arg0,body=B0}=Seq0, Ctxt, Sub) ->
%% Optimise away pure literal arg as its value is ignored.
B1 = body(B0, Ctxt, Sub),
Arg = body(Arg0, effect, Sub),
case will_fail(Arg) of
true ->
Arg;
false ->
%% Arg cannot be "values" here - only a single value
%% make sense here.
case is_safe_simple(Arg, Sub) of
true -> B1;
false -> Seq0#c_seq{arg=Arg,body=B1}
end
end;
expr(#c_let{}=Let0, Ctxt, Sub) ->
Let = opt_case_in_let(Let0),
case simplify_let(Let, Sub) of
impossible ->
%% The argument for the let is "simple", i.e. has no
%% complex structures such as let or seq that can be entered.
?ASSERT(verify_scope(Let, Sub)),
opt_simple_let(Let, Ctxt, Sub);
Expr ->
%% The let body was successfully moved into the let argument.
%% Now recursively re-process the new expression.
expr(Expr, Ctxt, sub_new_preserve_types(Sub))
end;
expr(#c_letrec{body=#c_var{}}=Letrec, effect, _Sub) ->
%% This is named fun in an 'effect' context. Warn and ignore.
add_warning(Letrec, useless_building),
void();
expr(#c_letrec{defs=Fs0,body=B0}=Letrec, Ctxt, Sub) ->
Fs1 = map(fun ({Name,Fb}) ->
{Name,expr(Fb, {letrec,Ctxt}, Sub)}
end, Fs0),
B1 = body(B0, Ctxt, Sub),
Letrec#c_letrec{defs=Fs1,body=B1};
expr(#c_case{}=Case0, Ctxt, Sub) ->
%% Ideally, the compiler should only emit warnings when there is
%% a real mistake in the code being compiled. We use the follow
%% heuristics in an attempt to approach that ideal:
%%
%% * If the guard for a clause always fails, we will emit a
%% warning.
%%
%% * If a case expression is a literal, we will emit no warnings
%% for clauses that will not match or for clauses that are
%% shadowed after a clause that will always match. That means
%% that code such as:
%%
%% case ?DEBUG of
%% false -> ok;
%% true -> ...
%% end
%%
%% (where ?DEBUG expands to either 'true' or 'false') will not
%% produce any warnings.
%%
%% * If the case expression is not literal, warnings will be
%% emitted for every clause that don't match and for all
%% clauses following a clause that will always match.
%%
%% * If no clause will ever match, there will be a warning
%% (in addition to any warnings that may have been emitted
%% according to the rules above).
%%
case opt_bool_case(Case0) of
#c_case{arg=Arg0,clauses=Cs0}=Case1 ->
Arg1 = body(Arg0, value, Sub),
LitExpr = cerl:is_literal(Arg1),
{Arg2,Cs1} = case_opt(Arg1, Cs0, Sub),
Cs2 = clauses(Arg2, Cs1, Ctxt, Sub, LitExpr),
Case = Case1#c_case{arg=Arg2,clauses=Cs2},
warn_no_clause_match(Case1, Case),
Expr = eval_case(Case, Sub),
case move_case_into_arg(Case, Sub) of
impossible ->
bsm_an(Expr);
Other ->
expr(Other, Ctxt, sub_new_preserve_types(Sub))
end;
Other ->
expr(Other, Ctxt, Sub)
end;
expr(#c_receive{clauses=Cs0,timeout=T0,action=A0}=Recv, Ctxt, Sub) ->
Cs1 = clauses(#c_var{name='_'}, Cs0, Ctxt, Sub, false),
T1 = expr(T0, value, Sub),
A1 = body(A0, Ctxt, Sub),
Recv#c_receive{clauses=Cs1,timeout=T1,action=A1};
expr(#c_apply{op=Op0,args=As0}=App, _, Sub) ->
Op1 = expr(Op0, value, Sub),
As1 = expr_list(As0, value, Sub),
App#c_apply{op=Op1,args=As1};
expr(#c_call{module=M0,name=N0}=Call0, Ctxt, Sub) ->
M1 = expr(M0, value, Sub),
N1 = expr(N0, value, Sub),
Call = Call0#c_call{module=M1,name=N1},
case useless_call(Ctxt, Call) of
no -> call(Call, M1, N1, Sub);
{yes,Seq} -> expr(Seq, Ctxt, Sub)
end;
expr(#c_primop{args=As0}=Prim, _, Sub) ->
As1 = expr_list(As0, value, Sub),
Prim#c_primop{args=As1};
expr(#c_catch{body=B0}=Catch, _, Sub) ->
%% We can remove catch if the value is simple
B1 = body(B0, value, Sub),
case is_safe_simple(B1, Sub) of
true -> B1;
false -> Catch#c_catch{body=B1}
end;
expr(#c_try{arg=E0,vars=[#c_var{name=X}],body=#c_var{name=X},
handler=#c_literal{val=false}=False}=Try, _, Sub) ->
%% Since guard may call expr/2, we must do some optimization of
%% the kind of try's that occur in guards.
E1 = body(E0, value, Sub),
case will_fail(E1) of
false ->
%% Remove any calls that are evaluated for effect only.
E2 = opt_guard_try(E1),
%% We can remove try/catch if the expression is an
%% expression that cannot fail.
case is_safe_bool_expr(E2, Sub) orelse is_safe_simple(E2, Sub) of
true -> E2;
false -> Try#c_try{arg=E2}
end;
true ->
%% Expression will always fail.
False
end;
expr(#c_try{anno=A,arg=E0,vars=Vs0,body=B0,evars=Evs0,handler=H0}=Try, _, Sub0) ->
%% Here is the general try/catch construct outside of guards.
%% We can remove try if the value is simple and replace it with a let.
E1 = body(E0, value, Sub0),
{Vs1,Sub1} = pattern_list(Vs0, Sub0),
B1 = body(B0, value, Sub1),
case is_safe_simple(E1, Sub0) of
true ->
expr(#c_let{anno=A,vars=Vs1,arg=E1,body=B1}, value, Sub0);
false ->
{Evs1,Sub2} = pattern_list(Evs0, Sub0),
H1 = body(H0, value, Sub2),
Try#c_try{arg=E1,vars=Vs1,body=B1,evars=Evs1,handler=H1}
end.
expr_list(Es, Ctxt, Sub) ->
[expr(E, Ctxt, Sub) || E <- Es].
pair_list(Es, Ctxt, Sub) ->
[pair(E, Ctxt, Sub) || E <- Es].
pair(#c_map_pair{key=K,val=V}, effect, Sub) ->
make_effect_seq([K,V], Sub);
pair(#c_map_pair{key=K0,val=V0}=Pair, value=Ctxt, Sub) ->
K = expr(K0, Ctxt, Sub),
V = expr(V0, Ctxt, Sub),
Pair#c_map_pair{key=K,val=V}.
bitstr_list(Es, Sub) ->
[bitstr(E, Sub) || E <- Es].
bitstr(#c_bitstr{val=Val,size=Size}=BinSeg, Sub) ->
BinSeg#c_bitstr{val=expr(Val, Sub),size=expr(Size, value, Sub)}.
%% is_safe_simple(Expr, Sub) -> true | false.
%% A safe simple cannot fail with badarg and is safe to use
%% in a guard.
%%
%% Currently, we don't attempt to check binaries because they
%% are difficult to check.
is_safe_simple(#c_var{}, _) -> true;
is_safe_simple(#c_cons{hd=H,tl=T}, Sub) ->
is_safe_simple(H, Sub) andalso is_safe_simple(T, Sub);
is_safe_simple(#c_tuple{es=Es}, Sub) -> is_safe_simple_list(Es, Sub);
is_safe_simple(#c_literal{}, _) -> true;
is_safe_simple(#c_call{module=#c_literal{val=erlang},
name=#c_literal{val=Name},
args=Args}, Sub) when is_atom(Name) ->
NumArgs = length(Args),
case erl_internal:bool_op(Name, NumArgs) of
true ->
%% Boolean operators are safe if the arguments are boolean.
all(fun(C) -> is_boolean_type(C, Sub) =:= yes end, Args);
false ->
%% We need a rather complicated test to ensure that
%% we only allow safe calls that are allowed in a guard.
%% (Note that is_function/2 is a type test, but is not safe.)
erl_bifs:is_safe(erlang, Name, NumArgs) andalso
(erl_internal:comp_op(Name, NumArgs) orelse
erl_internal:new_type_test(Name, NumArgs))
end;
is_safe_simple(_, _) -> false.
is_safe_simple_list(Es, Sub) -> all(fun(E) -> is_safe_simple(E, Sub) end, Es).
%% will_fail(Expr) -> true|false.
%% Determine whether the expression will fail with an exception.
%% Return true if the expression always will fail with an exception,
%% i.e. never return normally.
will_fail(#c_let{arg=A,body=B}) ->
will_fail(A) orelse will_fail(B);
will_fail(#c_call{module=#c_literal{val=Mod},name=#c_literal{val=Name},args=Args}) ->
erl_bifs:is_exit_bif(Mod, Name, length(Args));
will_fail(#c_primop{name=#c_literal{val=match_fail},args=[_]}) -> true;
will_fail(_) -> false.
%% bin_un_utf(#c_binary{}) -> #c_binary{}
%% Convert any literal UTF-8/16/32 literals to byte-sized
%% integer fields.
bin_un_utf(#c_binary{anno=Anno,segments=Ss}=Bin) ->
Bin#c_binary{segments=bin_un_utf_1(Ss, Anno)}.
bin_un_utf_1([#c_bitstr{val=#c_literal{},type=#c_literal{val=utf8}}=H|T],
Anno) ->
bin_un_utf_eval(H, Anno) ++ bin_un_utf_1(T, Anno);
bin_un_utf_1([#c_bitstr{val=#c_literal{},type=#c_literal{val=utf16}}=H|T],
Anno) ->
bin_un_utf_eval(H, Anno) ++ bin_un_utf_1(T, Anno);
bin_un_utf_1([#c_bitstr{val=#c_literal{},type=#c_literal{val=utf32}}=H|T],
Anno) ->
bin_un_utf_eval(H, Anno) ++ bin_un_utf_1(T, Anno);
bin_un_utf_1([H|T], Anno) ->
[H|bin_un_utf_1(T, Anno)];
bin_un_utf_1([], _) -> [].
bin_un_utf_eval(Bitstr, Anno) ->
Segments = [Bitstr],
case eval_binary(#c_binary{anno=Anno,segments=Segments}) of
#c_literal{anno=Anno,val=Bytes} when is_binary(Bytes) ->
[#c_bitstr{anno=Anno,
val=#c_literal{anno=Anno,val=B},
size=#c_literal{anno=Anno,val=8},
unit=#c_literal{anno=Anno,val=1},
type=#c_literal{anno=Anno,val=integer},
flags=#c_literal{anno=Anno,val=[unsigned,big]}} ||
B <- binary_to_list(Bytes)];
_ ->
Segments
end.
%% eval_binary(#c_binary{}) -> #c_binary{} | #c_literal{}
%% Evaluate a binary at compile time if possible to create
%% a binary literal.
eval_binary(#c_binary{anno=Anno,segments=Ss}=Bin) ->
try
#c_literal{anno=Anno,val=eval_binary_1(Ss, <<>>)}
catch
throw:impossible ->
Bin;
throw:{badarg,Warning} ->
add_warning(Bin, Warning),
#c_call{anno=Anno,
module=#c_literal{val=erlang},
name=#c_literal{val=error},
args=[#c_literal{val=badarg}]}
end.
eval_binary_1([#c_bitstr{val=#c_literal{val=Val},size=#c_literal{val=Sz},
unit=#c_literal{val=Unit},type=#c_literal{val=Type},
flags=#c_literal{val=Flags}}|Ss], Acc0) ->
Endian = case member(big, Flags) of
true ->
big;
false ->
case member(little, Flags) of
true -> little;
false -> throw(impossible) %Native endian.
end
end,
%% Make sure that the size is reasonable.
case Type of
binary when is_bitstring(Val) ->
if
Sz =:= all ->
ok;
Sz*Unit =< bit_size(Val) ->
ok;
true ->
%% Field size is greater than the actual binary - will fail.
throw({badarg,embedded_binary_size})
end;
integer when is_integer(Val) ->
%% Estimate the number of bits needed to to hold the integer
%% literal. Check whether the field size is reasonable in
%% proportion to the number of bits needed.
if
Sz*Unit =< 256 ->
%% Don't be cheap - always accept fields up to this size.
ok;
true ->
case count_bits(Val) of
BitsNeeded when 2*BitsNeeded >= Sz*Unit ->
ok;
_ ->
%% More than about half of the field size will be
%% filled out with zeroes - not acceptable.
throw(impossible)
end
end;
float when is_float(Val) ->
%% Bad float size.
case Sz*Unit of
32 -> ok;
64 -> ok;
_ -> throw(impossible)
end;
utf8 -> ok;
utf16 -> ok;
utf32 -> ok;
_ ->
throw(impossible)
end,
%% Evaluate the field.
try eval_binary_2(Acc0, Val, Sz, Unit, Type, Endian) of
Acc -> eval_binary_1(Ss, Acc)
catch
error:_ ->
throw(impossible)
end;
eval_binary_1([], Acc) -> Acc;
eval_binary_1(_, _) -> throw(impossible).
eval_binary_2(Acc, Val, Size, Unit, integer, little) ->
<<Acc/bitstring,Val:(Size*Unit)/little>>;
eval_binary_2(Acc, Val, Size, Unit, integer, big) ->
<<Acc/bitstring,Val:(Size*Unit)/big>>;
eval_binary_2(Acc, Val, _Size, _Unit, utf8, _) ->
try
<<Acc/bitstring,Val/utf8>>
catch
error:_ ->
throw({badarg,bad_unicode})
end;
eval_binary_2(Acc, Val, _Size, _Unit, utf16, big) ->
try
<<Acc/bitstring,Val/big-utf16>>
catch
error:_ ->
throw({badarg,bad_unicode})
end;
eval_binary_2(Acc, Val, _Size, _Unit, utf16, little) ->
try
<<Acc/bitstring,Val/little-utf16>>
catch
error:_ ->
throw({badarg,bad_unicode})
end;
eval_binary_2(Acc, Val, _Size, _Unit, utf32, big) ->
try
<<Acc/bitstring,Val/big-utf32>>
catch
error:_ ->
throw({badarg,bad_unicode})
end;
eval_binary_2(Acc, Val, _Size, _Unit, utf32, little) ->
try
<<Acc/bitstring,Val/little-utf32>>
catch
error:_ ->
throw({badarg,bad_unicode})
end;
eval_binary_2(Acc, Val, Size, Unit, float, little) ->
<<Acc/bitstring,Val:(Size*Unit)/little-float>>;
eval_binary_2(Acc, Val, Size, Unit, float, big) ->
<<Acc/bitstring,Val:(Size*Unit)/big-float>>;
eval_binary_2(Acc, Val, all, Unit, binary, _) ->
case bit_size(Val) of
Size when Size rem Unit =:= 0 ->
<<Acc/bitstring,Val:Size/bitstring>>;
Size ->
throw({badarg,{embedded_unit,Unit,Size}})
end;
eval_binary_2(Acc, Val, Size, Unit, binary, _) ->
<<Acc/bitstring,Val:(Size*Unit)/bitstring>>.
%% Count the number of bits approximately needed to store Int.
%% (We don't need an exact result for this purpose.)
count_bits(Int) ->
count_bits_1(abs(Int), 64).
count_bits_1(0, Bits) -> Bits;
count_bits_1(Int, Bits) -> count_bits_1(Int bsr 64, Bits+64).
%% useless_call(Context, #c_call{}) -> no | {yes,Expr}
%% Check whether the function is called only for effect,
%% and if the function either has no effect whatsoever or
%% the only effect is an exception. Generate appropriate
%% warnings. If the call is "useless" (has no effect),
%% a rewritten expression consisting of a sequence of
%% the arguments only is returned.
useless_call(effect, #c_call{module=#c_literal{val=Mod},
name=#c_literal{val=Name},
args=Args}=Call) ->
A = length(Args),
case erl_bifs:is_safe(Mod, Name, A) of
false ->
case erl_bifs:is_pure(Mod, Name, A) of
true -> add_warning(Call, result_ignored);
false -> ok
end,
no;
true ->
add_warning(Call, {no_effect,{Mod,Name,A}}),
{yes,make_effect_seq(Args, sub_new())}
end;
useless_call(_, _) -> no.
%% make_effect_seq([Expr], Sub) -> #c_seq{}|void()
%% Convert a list of expressions evaluated in effect context to a chain of
%% #c_seq{}. The body in the innermost #c_seq{} will be void().
%% Anything that will not have any effect will be thrown away.
make_effect_seq([H|T], Sub) ->
case is_safe_simple(H, Sub) of
true -> make_effect_seq(T, Sub);
false -> #c_seq{arg=H,body=make_effect_seq(T, Sub)}
end;
make_effect_seq([], _) -> void().
%% Handling remote calls. The module/name fields have been processed.
call(#c_call{args=As}=Call, #c_literal{val=M}=M0, #c_literal{val=N}=N0, Sub) ->
case get(no_inline_list_funcs) of
true ->
call_1(Call, M0, N0, As, Sub);
false ->
case sys_core_fold_lists:call(Call, M, N, As) of
none ->
call_1(Call, M, N, As, Sub);
Core ->
expr(Core, Sub)
end
end;
call(#c_call{args=As}=Call, M, N, Sub) ->
call_1(Call, M, N, As, Sub).
call_1(Call, M, N, As0, Sub) ->
As1 = expr_list(As0, value, Sub),
fold_call(Call#c_call{args=As1}, M, N, As1, Sub).
%% fold_call(Call, Mod, Name, Args, Sub) -> Expr.
%% Try to safely evaluate the call. Just try to evaluate arguments,
%% do the call and convert return values to literals. If this
%% succeeds then use the new value, otherwise just fail and use
%% original call. Do this at every level.
%%
%% We attempt to evaluate calls to certain BIFs even if the
%% arguments are not literals. For instance, we evaluate length/1
%% if the shape of the list is known, and element/2 and setelement/3
%% if the position is constant and the shape of the tuple is known.
%%
fold_call(Call, #c_literal{val=M}, #c_literal{val=F}, Args, Sub) ->
fold_call_1(Call, M, F, Args, Sub);
fold_call(Call, _M, _N, _Args, _Sub) -> Call.
fold_call_1(Call, erlang, apply, [Mod,Func,Args], _) ->
simplify_apply(Call, Mod, Func, Args);
fold_call_1(Call, Mod, Name, Args, Sub) ->
NumArgs = length(Args),
case erl_bifs:is_pure(Mod, Name, NumArgs) of
false -> Call; %Not pure - keep call.
true -> fold_call_2(Call, Mod, Name, Args, Sub)
end.
fold_call_2(Call, Module, Name, Args, Sub) ->
case all(fun cerl:is_literal/1, Args) of
true ->
%% All arguments are literals.
fold_lit_args(Call, Module, Name, Args);
false ->
%% At least one non-literal argument.
fold_non_lit_args(Call, Module, Name, Args, Sub)
end.
fold_lit_args(Call, Module, Name, Args0) ->
Args = [cerl:concrete(A) || A <- Args0],
try apply(Module, Name, Args) of
Val ->
case cerl:is_literal_term(Val) of
true ->
cerl:abstract(Val);
false ->
%% Successful evaluation, but it was not possible
%% to express the computed value as a literal.
Call
end
catch
error:Reason ->
%% Evaluation of the function failed. Warn and replace
%% the call with a call to erlang:error/1.
eval_failure(Call, Reason)
end.
%% fold_non_lit_args(Call, Module, Name, Args, Sub) -> Expr.
%% Attempt to evaluate some pure BIF calls with one or more
%% non-literals arguments.
%%
fold_non_lit_args(Call, erlang, is_boolean, [Arg], Sub) ->
eval_is_boolean(Call, Arg, Sub);
fold_non_lit_args(Call, erlang, element, [Arg1,Arg2], Sub) ->
eval_element(Call, Arg1, Arg2, Sub);
fold_non_lit_args(Call, erlang, length, [Arg], _) ->
eval_length(Call, Arg);
fold_non_lit_args(Call, erlang, '++', [Arg1,Arg2], _) ->
eval_append(Call, Arg1, Arg2);
fold_non_lit_args(Call, lists, append, [Arg1,Arg2], _) ->
eval_append(Call, Arg1, Arg2);
fold_non_lit_args(Call, erlang, setelement, [Arg1,Arg2,Arg3], _) ->
eval_setelement(Call, Arg1, Arg2, Arg3);
fold_non_lit_args(Call, erlang, is_record, [Arg1,Arg2,Arg3], Sub) ->
eval_is_record(Call, Arg1, Arg2, Arg3, Sub);
fold_non_lit_args(Call, erlang, N, Args, Sub) ->
NumArgs = length(Args),
case erl_internal:comp_op(N, NumArgs) of
true ->
eval_rel_op(Call, N, Args, Sub);
false ->
case erl_internal:bool_op(N, NumArgs) of
true ->
eval_bool_op(Call, N, Args, Sub);
false ->
Call
end
end;
fold_non_lit_args(Call, _, _, _, _) -> Call.
%% Evaluate a relational operation using type information.
eval_rel_op(Call, Op, [#c_var{name=V},#c_var{name=V}], _) ->
Bool = erlang:Op(same, same),
#c_literal{anno=cerl:get_ann(Call),val=Bool};
eval_rel_op(Call, '=:=', [Term,#c_literal{val=true}], Sub) ->
%% BoolVar =:= true ==> BoolVar
case is_boolean_type(Term, Sub) of
yes -> Term;
maybe -> Call;
no -> #c_literal{val=false}
end;
eval_rel_op(Call, '==', Ops, Sub) ->
case is_exact_eq_ok(Ops, Sub) of
true ->
Name = #c_literal{anno=cerl:get_ann(Call),val='=:='},
Call#c_call{name=Name};
false ->
Call
end;
eval_rel_op(Call, '/=', Ops, Sub) ->
case is_exact_eq_ok(Ops, Sub) of
true ->
Name = #c_literal{anno=cerl:get_ann(Call),val='=/='},
Call#c_call{name=Name};
false ->
Call
end;
eval_rel_op(Call, _, _, _) -> Call.
is_exact_eq_ok([A,B]=L, Sub) ->
case is_int_type(A, Sub) =:= yes andalso is_int_type(B, Sub) =:= yes of
true -> true;
false -> is_exact_eq_ok_1(L)
end.
is_exact_eq_ok_1([#c_literal{val=Lit}|_]) ->
is_non_numeric(Lit);
is_exact_eq_ok_1([_|T]) ->
is_exact_eq_ok_1(T);
is_exact_eq_ok_1([]) -> false.
is_non_numeric([H|T]) ->
is_non_numeric(H) andalso is_non_numeric(T);
is_non_numeric(Tuple) when is_tuple(Tuple) ->
is_non_numeric_tuple(Tuple, tuple_size(Tuple));
is_non_numeric(Map) when is_map(Map) ->
%% Note that 17.x and 18.x compare keys in different ways.
%% Be very conservative -- require that both keys and values
%% are non-numeric.
is_non_numeric(maps:to_list(Map));
is_non_numeric(Num) when is_number(Num) ->
false;
is_non_numeric(_) -> true.
is_non_numeric_tuple(Tuple, El) when El >= 1 ->
is_non_numeric(element(El, Tuple)) andalso
is_non_numeric_tuple(Tuple, El-1);
is_non_numeric_tuple(_Tuple, 0) -> true.
%% Evaluate a bool op using type information. We KNOW that
%% there must be at least one non-literal argument (i.e.
%% there is no need to handle the case that all argments
%% are literal).
eval_bool_op(Call, 'and', [#c_literal{val=true},Term], Sub) ->
eval_bool_op_1(Call, Term, Term, Sub);
eval_bool_op(Call, 'and', [Term,#c_literal{val=true}], Sub) ->
eval_bool_op_1(Call, Term, Term, Sub);
eval_bool_op(Call, 'and', [#c_literal{val=false}=Res,Term], Sub) ->
eval_bool_op_1(Call, Res, Term, Sub);
eval_bool_op(Call, 'and', [Term,#c_literal{val=false}=Res], Sub) ->
eval_bool_op_1(Call, Res, Term, Sub);
eval_bool_op(Call, _, _, _) -> Call.
eval_bool_op_1(Call, Res, Term, Sub) ->
case is_boolean_type(Term, Sub) of
yes -> Res;
no -> eval_failure(Call, badarg);
maybe -> Call
end.
%% Evaluate is_boolean/1 using type information.
eval_is_boolean(Call, Term, Sub) ->
case is_boolean_type(Term, Sub) of
no -> #c_literal{val=false};
yes -> #c_literal{val=true};
maybe -> Call
end.
%% eval_length(Call, List) -> Val.
%% Evaluates the length for the prefix of List which has a known
%% shape.
%%
eval_length(Call, Core) -> eval_length(Call, Core, 0).
eval_length(Call, #c_literal{val=Val}, Len0) ->
try
Len = Len0 + length(Val),
#c_literal{anno=Call#c_call.anno,val=Len}
catch
_:_ ->
eval_failure(Call, badarg)
end;
eval_length(Call, #c_cons{tl=T}, Len) ->
eval_length(Call, T, Len+1);
eval_length(Call, _List, 0) ->
Call; %Could do nothing
eval_length(Call, List, Len) ->
A = Call#c_call.anno,
#c_call{anno=A,
module=#c_literal{anno=A,val=erlang},
name=#c_literal{anno=A,val='+'},
args=[#c_literal{anno=A,val=Len},Call#c_call{args=[List]}]}.
%% eval_append(Call, FirstList, SecondList) -> Val.
%% Evaluates the constant part of '++' expression.
%%
eval_append(Call, #c_literal{val=Cs1}=S1, #c_literal{val=Cs2}) ->
try
S1#c_literal{val=Cs1 ++ Cs2}
catch error:badarg ->
eval_failure(Call, badarg)
end;
eval_append(Call, #c_literal{val=Cs}, List) when length(Cs) =< 4 ->
Anno = Call#c_call.anno,
foldr(fun (C, L) ->
ann_c_cons(Anno, #c_literal{val=C}, L)
end, List, Cs);
eval_append(Call, #c_cons{anno=Anno,hd=H,tl=T}, List) ->
ann_c_cons(Anno, H, eval_append(Call, T, List));
eval_append(Call, X, Y) ->
Call#c_call{args=[X,Y]}. %Rebuild call arguments.
%% eval_element(Call, Pos, Tuple, Types) -> Val.
%% Evaluates element/2 if the position Pos is a literal and
%% the shape of the tuple Tuple is known.
%%
eval_element(Call, #c_literal{val=Pos}, Tuple, Types)
when is_integer(Pos) ->
case get_type(Tuple, Types) of
none ->
Call;
Type ->
Es = case cerl:is_c_tuple(Type) of
false -> [];
true -> cerl:tuple_es(Type)
end,
if
1 =< Pos, Pos =< length(Es) ->
El = lists:nth(Pos, Es),
try
cerl:set_ann(pat_to_expr(El), [compiler_generated])
catch
throw:impossible ->
Call
end;
true ->
%% Index outside tuple or not a tuple.
eval_failure(Call, badarg)
end
end;
eval_element(Call, Pos, Tuple, Sub) ->
case is_int_type(Pos, Sub) =:= no orelse
is_tuple_type(Tuple, Sub) =:= no of
true ->
eval_failure(Call, badarg);
false ->
Call
end.
%% eval_is_record(Call, Var, Tag, Size, Types) -> Val.
%% Evaluates is_record/3 using type information.
%%
eval_is_record(Call, Term, #c_literal{val=NeededTag},
#c_literal{val=Size}, Types) ->
case get_type(Term, Types) of
none ->
Call;
Type ->
Es = case cerl:is_c_tuple(Type) of
false -> [];
true -> cerl:tuple_es(Type)
end,
case Es of
[#c_literal{val=Tag}|_] ->
Bool = Tag =:= NeededTag andalso
length(Es) =:= Size,
#c_literal{val=Bool};
_ ->
#c_literal{val=false}
end
end;
eval_is_record(Call, _, _, _, _) -> Call.
%% eval_setelement(Call, Pos, Tuple, NewVal) -> Core.
%% Evaluates setelement/3 if position Pos is an integer
%% and the shape of the tuple Tuple is known.
%%
eval_setelement(Call, #c_literal{val=Pos}, Tuple, NewVal)
when is_integer(Pos) ->
case cerl:is_data(Tuple) of
false ->
Call;
true ->
Es0 = case cerl:is_c_tuple(Tuple) of
false -> [];
true -> cerl:tuple_es(Tuple)
end,
if
1 =< Pos, Pos =< length(Es0) ->
Es = eval_setelement_1(Pos, Es0, NewVal),
cerl:update_c_tuple(Tuple, Es);
true ->
eval_failure(Call, badarg)
end
end;
eval_setelement(Call, _, _, _) -> Call.
eval_setelement_1(1, [_|T], NewVal) ->
[NewVal|T];
eval_setelement_1(Pos, [H|T], NewVal) when Pos > 1 ->
[H|eval_setelement_1(Pos-1, T, NewVal)].
%% eval_failure(Call, Reason) -> Core.
%% Warn for a call that will fail and replace the call with
%% a call to erlang:error(Reason).
%%
eval_failure(Call, Reason) ->
add_warning(Call, {eval_failure,Reason}),
Call#c_call{module=#c_literal{val=erlang},
name=#c_literal{val=error},
args=[#c_literal{val=Reason}]}.
%% simplify_apply(Call0, Mod, Func, Args) -> Call
%% Simplify an apply/3 to a call if the number of arguments
%% are known at compile time.
simplify_apply(Call, Mod, Func, Args) ->
case is_atom_or_var(Mod) andalso is_atom_or_var(Func) of
true -> simplify_apply_1(Args, Call, Mod, Func, []);
false -> Call
end.
simplify_apply_1(#c_literal{val=MoreArgs0}, Call, Mod, Func, Args)
when length(MoreArgs0) >= 0 ->
MoreArgs = [#c_literal{val=Arg} || Arg <- MoreArgs0],
Call#c_call{module=Mod,name=Func,args=reverse(Args, MoreArgs)};
simplify_apply_1(#c_cons{hd=Arg,tl=T}, Call, Mod, Func, Args) ->
simplify_apply_1(T, Call, Mod, Func, [Arg|Args]);
simplify_apply_1(_, Call, _, _, _) -> Call.
is_atom_or_var(#c_literal{val=Atom}) when is_atom(Atom) -> true;
is_atom_or_var(#c_var{}) -> true;
is_atom_or_var(_) -> false.
%% clause(Clause, Cepxr, Context, Sub) -> Clause.
clause(#c_clause{pats=Ps0,guard=G0,body=B0}=Cl, Cexpr, Ctxt, Sub0) ->
{Ps1,Sub1} = pattern_list(Ps0, Sub0),
Sub2 = update_types(Cexpr, Ps1, Sub1),
GSub = case {Cexpr,Ps1} of
{#c_var{name='_'},_} ->
%% In a 'receive', Cexpr is the variable '_', which represents the
%% message being matched. We must NOT do any extra substiutions.
Sub2;
{#c_var{},[#c_var{}=Var]} ->
%% The idea here is to optimize expressions such as
%%
%% case A of A -> ...
%%
%% to get rid of the extra guard test that the compiler
%% added when converting to the Core Erlang representation:
%%
%% case A of NewVar when A =:= NewVar -> ...
%%
%% By replacing NewVar with A everywhere in the guard
%% expression, we get
%%
%% case A of NewVar when A =:= A -> ...
%%
%% which by constant-expression evaluation is reduced to
%%
%% case A of NewVar when true -> ...
%%
sub_set_var(Var, Cexpr, Sub2);
_ ->
Sub2
end,
G1 = guard(G0, GSub),
B1 = body(B0, Ctxt, Sub2),
Cl#c_clause{pats=Ps1,guard=G1,body=B1}.
%% let_substs(LetVars, LetArg, Sub) -> {[Var],[Val],Sub}.
%% Add suitable substitutions to Sub of variables in LetVars. First
%% remove variables in LetVars from Sub, then fix subs. N.B. must
%% work out new subs in parallel and then apply them to subs. Return
%% the unsubstituted variables and values.
let_substs(Vs0, As0, Sub0) ->
{Vs1,Sub1} = pattern_list(Vs0, Sub0),
{Vs2,As1,Ss} = let_substs_1(Vs1, As0, Sub1),
Sub2 = sub_add_scope([V || #c_var{name=V} <- Vs2], Sub1),
{Vs2,As1,
foldl(fun ({V,S}, Sub) -> sub_set_name(V, S, Sub) end, Sub2, Ss)}.
let_substs_1(Vs, #c_values{es=As}, Sub) ->
let_subst_list(Vs, As, Sub);
let_substs_1([V], A, Sub) -> let_subst_list([V], [A], Sub);
let_substs_1(Vs, A, _) -> {Vs,A,[]}.
let_subst_list([V|Vs0], [A0|As0], Sub) ->
{Vs1,As1,Ss} = let_subst_list(Vs0, As0, Sub),
case is_subst(A0) of
true ->
A = case is_compiler_generated(V) andalso
not is_compiler_generated(A0) of
true ->
%% Propagate the 'compiler_generated' annotation
%% along with the value.
Ann = [compiler_generated|cerl:get_ann(A0)],
cerl:set_ann(A0, Ann);
false ->
A0
end,
{Vs1,As1,sub_subst_var(V, A, Sub) ++ Ss};
false ->
{[V|Vs1],[A0|As1],Ss}
end;
let_subst_list([], [], _) -> {[],[],[]}.
%% pattern(Pattern, InSub) -> {Pattern,OutSub}.
%% pattern(Pattern, InSub, OutSub) -> {Pattern,OutSub}.
%% Variables occurring in Pattern will shadow so they must be removed
%% from Sub. If they occur as a value in Sub then we create a new
%% variable and then add a substitution for that.
%%
%% Patterns are complicated by sizes in binaries. These are pure
%% input variables which create no bindings. We, therefore, need to
%% carry around the original substitutions to get the correct
%% handling.
%%pattern(Pat, Sub) -> pattern(Pat, Sub, Sub).
pattern(#c_var{}=Pat, Isub, Osub) ->
case sub_is_val(Pat, Isub) of
true ->
V1 = make_var_name(),
Pat1 = #c_var{name=V1},
{Pat1,sub_set_var(Pat, Pat1, sub_add_scope([V1], Osub))};
false ->
{Pat,sub_del_var(Pat, Osub)}
end;
pattern(#c_literal{}=Pat, _, Osub) -> {Pat,Osub};
pattern(#c_cons{anno=Anno,hd=H0,tl=T0}, Isub, Osub0) ->
{H1,Osub1} = pattern(H0, Isub, Osub0),
{T1,Osub2} = pattern(T0, Isub, Osub1),
{ann_c_cons(Anno, H1, T1),Osub2};
pattern(#c_tuple{anno=Anno,es=Es0}, Isub, Osub0) ->
{Es1,Osub1} = pattern_list(Es0, Isub, Osub0),
{ann_c_tuple(Anno, Es1),Osub1};
pattern(#c_map{anno=Anno,es=Es0}=Map, Isub, Osub0) ->
{Es1,Osub1} = map_pair_pattern_list(Es0, Isub, Osub0),
{Map#c_map{anno=Anno,es=Es1},Osub1};
pattern(#c_binary{segments=V0}=Pat, Isub, Osub0) ->
{V1,Osub1} = bin_pattern_list(V0, Isub, Osub0),
{Pat#c_binary{segments=V1},Osub1};
pattern(#c_alias{var=V0,pat=P0}=Pat, Isub, Osub0) ->
{V1,Osub1} = pattern(V0, Isub, Osub0),
{P1,Osub2} = pattern(P0, Isub, Osub1),
Osub = update_types(V1, [P1], Osub2),
{Pat#c_alias{var=V1,pat=P1},Osub}.
map_pair_pattern_list(Ps0, Isub, Osub0) ->
{Ps,{_,Osub}} = mapfoldl(fun map_pair_pattern/2, {Isub,Osub0}, Ps0),
{Ps,Osub}.
map_pair_pattern(#c_map_pair{op=#c_literal{val=exact},key=K0,val=V0}=Pair,{Isub,Osub0}) ->
K = expr(K0, Isub),
{V,Osub} = pattern(V0,Isub,Osub0),
{Pair#c_map_pair{key=K,val=V},{Isub,Osub}}.
bin_pattern_list(Ps0, Isub, Osub0) ->
{Ps,{_,Osub}} = mapfoldl(fun bin_pattern/2, {Isub,Osub0}, Ps0),
{Ps,Osub}.
bin_pattern(#c_bitstr{val=E0,size=Size0}=Pat, {Isub0,Osub0}) ->
Size1 = expr(Size0, Isub0),
{E1,Osub} = pattern(E0, Isub0, Osub0),
Isub = case E0 of
#c_var{} -> sub_set_var(E0, E1, Isub0);
_ -> Isub0
end,
{Pat#c_bitstr{val=E1,size=Size1},{Isub,Osub}}.
pattern_list(Ps, Sub) -> pattern_list(Ps, Sub, Sub).
pattern_list(Ps0, Isub, Osub0) ->
mapfoldl(fun (P, Osub) -> pattern(P, Isub, Osub) end, Osub0, Ps0).
%% is_subst(Expr) -> true | false.
%% Test whether an expression is a suitable substitution.
is_subst(#c_var{name={_,_}}) ->
%% Funs must not be duplicated (which will happen if the variable
%% is used more than once), because the funs will not be equal
%% (their "index" fields will be different).
false;
is_subst(#c_var{}) -> true;
is_subst(#c_literal{}) -> true;
is_subst(_) -> false.
%% sub_new() -> #sub{}.
%% sub_get_var(Var, #sub{}) -> Value.
%% sub_set_var(Var, Value, #sub{}) -> #sub{}.
%% sub_set_name(Name, Value, #sub{}) -> #sub{}.
%% sub_del_var(Var, #sub{}) -> #sub{}.
%% sub_subst_var(Var, Value, #sub{}) -> [{Name,Value}].
%% sub_is_val(Var, #sub{}) -> boolean().
%% sub_add_scope(#sub{}) -> #sub{}
%% sub_subst_scope(#sub{}) -> #sub{}
%%
%% We use the variable name as key so as not have problems with
%% annotations. When adding a new substitute we fold substitute
%% chains so we never have to search more than once. Use orddict so
%% we know the format.
%%
%% In addition to the list of substitutions, we also keep track of
%% all variable currently live (the scope).
%%
%% sub_add_scope/2 adds variables to the scope. sub_subst_scope/1
%% adds dummy substitutions for all variables in the scope in order
%% to force renaming if variables in the scope occurs as pattern
%% variables.
sub_new() -> #sub{v=orddict:new(),s=cerl_sets:new(),t=#{}}.
sub_new(#sub{}=Sub) ->
Sub#sub{v=orddict:new(),t=#{}}.
sub_new_preserve_types(#sub{}=Sub) ->
Sub#sub{v=orddict:new()}.
sub_get_var(#c_var{name=V}=Var, #sub{v=S}) ->
case orddict:find(V, S) of
{ok,Val} -> Val;
error -> Var
end.
sub_set_var(#c_var{name=V}, Val, Sub) ->
sub_set_name(V, Val, Sub).
sub_set_name(V, Val, #sub{v=S,s=Scope,t=Tdb0}=Sub) ->
Tdb1 = kill_types(V, Tdb0),
Tdb = copy_type(V, Val, Tdb1),
Sub#sub{v=orddict:store(V, Val, S),s=cerl_sets:add_element(V, Scope),t=Tdb}.
sub_del_var(#c_var{name=V}, #sub{v=S,s=Scope,t=Tdb}=Sub) ->
%% Profiling shows that for programs with many record operations,
%% sub_del_var/2 is a bottleneck. Since the scope contains all
%% variables that are live, we know that V cannot be present in S
%% if it is not in the scope.
case cerl_sets:is_element(V, Scope) of
false ->
Sub#sub{s=cerl_sets:add_element(V, Scope)};
true ->
Sub#sub{v=orddict:erase(V, S),t=kill_types(V, Tdb)}
end.
sub_subst_var(#c_var{name=V}, Val, #sub{v=S0}) ->
%% Fold chained substitutions.
[{V,Val}] ++ [ {K,Val} || {K,#c_var{name=V1}} <- S0, V1 =:= V].
sub_add_scope(Vs, #sub{s=Scope0}=Sub) ->
Scope = foldl(fun(V, S) when is_integer(V); is_atom(V) ->
cerl_sets:add_element(V, S)
end, Scope0, Vs),
Sub#sub{s=Scope}.
sub_subst_scope(#sub{v=S0,s=Scope}=Sub) ->
S = [{-1,#c_var{name=Sv}} || Sv <- cerl_sets:to_list(Scope)]++S0,
Sub#sub{v=S}.
sub_is_val(#c_var{name=V}, #sub{v=S,s=Scope}) ->
%% When the bottleneck in sub_del_var/2 was eliminated, this
%% became the new bottleneck. Since the scope contains all
%% live variables, a variable V can only be the target for
%% a substitution if it is in the scope.
cerl_sets:is_element(V, Scope) andalso v_is_value(V, S).
v_is_value(Var, [{_,#c_var{name=Var}}|_]) -> true;
v_is_value(Var, [_|T]) -> v_is_value(Var, T);
v_is_value(_, []) -> false.
%% warn_no_clause_match(CaseOrig, CaseOpt) -> ok
%% Generate a warning if none of the user-specified clauses
%% will match.
warn_no_clause_match(CaseOrig, CaseOpt) ->
OrigCs = cerl:case_clauses(CaseOrig),
OptCs = cerl:case_clauses(CaseOpt),
case any(fun(C) -> not is_compiler_generated(C) end, OrigCs) andalso
all(fun is_compiler_generated/1, OptCs) of
true ->
%% The original list of clauses did contain at least one
%% user-specified clause, but none of them will match.
%% That is probably a mistake.
add_warning(CaseOrig, no_clause_match);
false ->
%% Either there were user-specified clauses left in
%% the transformed clauses, or else none of the original
%% clauses were user-specified to begin with (as in 'andalso').
ok
end.
%% clauses(E, [Clause], TopLevel, Context, Sub) -> [Clause].
%% Trim the clauses by removing all clauses AFTER the first one which
%% is guaranteed to match. Also remove all trivially false clauses.
clauses(E, [C0|Cs], Ctxt, Sub, LitExpr) ->
#c_clause{pats=Ps,guard=G} = C1 = clause(C0, E, Ctxt, Sub),
%%ok = io:fwrite("~w: ~p~n", [?LINE,{E,Ps}]),
case {will_match(E, Ps),will_succeed(G)} of
{yes,yes} ->
case LitExpr of
false ->
Line = get_line(cerl:get_ann(C1)),
shadow_warning(Cs, Line);
true ->
%% If the case expression is a literal,
%% it is probably OK that some clauses don't match.
%% It is a probably some sort of debug macro.
ok
end,
[C1]; %Skip the rest
{_Mat,no} -> %Guard fails.
add_warning(C1, nomatch_guard),
clauses(E, Cs, Ctxt, Sub, LitExpr); %Skip this clause
{_Mat,_Suc} ->
[C1|clauses(E, Cs, Ctxt, Sub, LitExpr)]
end;
clauses(_, [], _, _, _) -> [].
shadow_warning([C|Cs], none) ->
add_warning(C, nomatch_shadow),
shadow_warning(Cs, none);
shadow_warning([C|Cs], Line) ->
add_warning(C, {nomatch_shadow, Line}),
shadow_warning(Cs, Line);
shadow_warning([], _) -> ok.
%% will_succeed(Guard) -> yes | maybe | no.
%% Test if we know whether a guard will succeed/fail or just don't
%% know. Be VERY conservative!
will_succeed(#c_literal{val=true}) -> yes;
will_succeed(#c_literal{val=false}) -> no;
will_succeed(_Guard) -> maybe.
%% will_match(Expr, [Pattern]) -> yes | maybe.
%% We KNOW that this function is only used after optimizations
%% in case_opt/4. Therefore clauses that can definitely not match
%% have already been pruned.
will_match(#c_values{es=Es}, Ps) ->
will_match_1(cerl_clauses:match_list(Ps, Es));
will_match(E, [P]) ->
will_match_1(cerl_clauses:match(P, E)).
will_match_1({false,_}) -> maybe;
will_match_1({true,_}) -> yes.
%% opt_bool_case(CoreExpr) - CoreExpr'.
%% Do various optimizations to case statement that has a
%% boolean case expression.
%%
%% We start with some simple optimizations and normalization
%% to facilitate later optimizations.
%%
%% If the case expression can only return a boolean
%% (or fail), we can remove any clause that cannot
%% possibly match 'true' or 'false'. Also, any clause
%% following both 'true' and 'false' clause can
%% be removed. If successful, we will end up this:
%%
%% case BoolExpr of case BoolExpr of
%% true -> false ->
%% ...; ...;
%% false -> OR true ->
%% ... ...
%% end. end.
%%
%% We give up if there are clauses with guards, or if there
%% is a variable clause that matches anything.
%%
opt_bool_case(#c_case{arg=Arg}=Case0) ->
case is_bool_expr(Arg) of
false ->
Case0;
true ->
try opt_bool_clauses(Case0) of
Case ->
opt_bool_not(Case)
catch
impossible ->
Case0
end
end;
opt_bool_case(Core) -> Core.
opt_bool_clauses(#c_case{clauses=Cs}=Case) ->
Case#c_case{clauses=opt_bool_clauses(Cs, false, false)}.
opt_bool_clauses(Cs, true, true) ->
%% We have now seen clauses that match both true and false.
%% Any remaining clauses cannot possibly match.
case Cs of
[_|_] ->
shadow_warning(Cs, none),
[];
[] ->
[]
end;
opt_bool_clauses([#c_clause{pats=[#c_literal{val=Lit}],
guard=#c_literal{val=true},
body=B}=C0|Cs], SeenT, SeenF) ->
case is_boolean(Lit) of
false ->
%% Not a boolean - this clause can't match.
add_warning(C0, nomatch_clause_type),
opt_bool_clauses(Cs, SeenT, SeenF);
true ->
%% This clause will match.
C = C0#c_clause{body=opt_bool_case(B)},
case {Lit,SeenT,SeenF} of
{false,_,false} ->
[C|opt_bool_clauses(Cs, SeenT, true)];
{true,false,_} ->
[C|opt_bool_clauses(Cs, true, SeenF)];
_ ->
add_warning(C, nomatch_shadow),
opt_bool_clauses(Cs, SeenT, SeenF)
end
end;
opt_bool_clauses([#c_clause{pats=Ps,guard=#c_literal{val=true}}=C|Cs], SeenT, SeenF) ->
case Ps of
[#c_var{}] ->
%% Will match a boolean.
throw(impossible);
[#c_alias{}] ->
%% Might match a boolean.
throw(impossible);
_ ->
%% The clause cannot possible match a boolean.
%% We can remove it.
add_warning(C, nomatch_clause_type),
opt_bool_clauses(Cs, SeenT, SeenF)
end;
opt_bool_clauses([_|_], _, _) ->
%% A clause with a guard. Give up.
throw(impossible).
%% We intentionally do not have a clause that match an empty
%% list. An empty list would indicate that the clauses do not
%% match all possible values for the case expression, which
%% means that the Core Erlang program is illegal. We prefer to
%% crash on such illegal input, rather than producing code that will
%% fail mysteriously at run time.
%% opt_bool_not(Case) -> CoreExpr.
%% Try to eliminate one or more calls to 'not' at the top level
%% of the case expression.
%%
%% We KNOW that the case expression is guaranteed to return
%% a boolean and that there are exactly two clauses: one that
%% matches 'true' and one that matches 'false'.
%%
%% case not Expr of case Expr of
%% true -> false ->
%% ...; ...;
%% false -> ==> true ->
%% ... ...;
%% end. NewVar ->
%% erlang:error(badarg)
%% end.
opt_bool_not(#c_case{arg=Arg,clauses=Cs0}=Case0) ->
case Arg of
#c_call{anno=Anno,module=#c_literal{val=erlang},
name=#c_literal{val='not'},
args=[Expr]} ->
Cs = [opt_bool_not_invert(C) || C <- Cs0] ++
[#c_clause{anno=[compiler_generated],
pats=[#c_var{name=cor_variable}],
guard=#c_literal{val=true},
body=#c_call{anno=Anno,
module=#c_literal{val=erlang},
name=#c_literal{val=error},
args=[#c_literal{val=badarg}]}}],
Case = Case0#c_case{arg=Expr,clauses=Cs},
opt_bool_not(Case);
_ ->
opt_bool_case_redundant(Case0)
end.
opt_bool_not_invert(#c_clause{pats=[#c_literal{val=Bool}]}=C) ->
C#c_clause{pats=[#c_literal{val=not Bool}]}.
%% opt_bool_case_redundant(Core) -> Core'.
%% If the sole purpose of the case is to verify that the case
%% expression is indeed boolean, we do not need the case
%% (since we have already verified that the case expression is
%% boolean).
%%
%% case BoolExpr of
%% true -> true ==> BoolExpr
%% false -> false
%% end.
%%
opt_bool_case_redundant(#c_case{arg=Arg,clauses=Cs}=Case) ->
case all(fun opt_bool_case_redundant_1/1, Cs) of
true -> Arg;
false -> opt_bool_case_guard(Case)
end.
opt_bool_case_redundant_1(#c_clause{pats=[#c_literal{val=B}],
body=#c_literal{val=B}}) ->
true;
opt_bool_case_redundant_1(_) -> false.
%% opt_bool_case_guard(Case) -> Case'.
%% Move a boolean case expression into the guard if we are sure that
%% it cannot fail.
%%
%% case SafeBoolExpr of case <> of
%% true -> TrueClause; ==> <> when SafeBoolExpr -> TrueClause;
%% false -> FalseClause <> when true -> FalseClause
%% end. end.
%%
%% Generally, evaluting a boolean expression in a guard should
%% be faster than evaulating it in the body.
%%
opt_bool_case_guard(#c_case{arg=#c_literal{}}=Case) ->
%% It is not necessary to move a literal case expression into the
%% guard, because it will be handled quite well in other
%% optimizations, and moving the literal into the guard will
%% cause some extra warnings, for instance for this code
%%
%% case true of
%% true -> ...;
%% false -> ...
%% end.
%%
Case;
opt_bool_case_guard(#c_case{arg=Arg,clauses=Cs0}=Case) ->
case is_safe_bool_expr(Arg, sub_new()) of
false ->
Case;
true ->
Cs = opt_bool_case_guard(Arg, Cs0),
Case#c_case{arg=#c_values{anno=cerl:get_ann(Arg),es=[]},
clauses=Cs}
end.
opt_bool_case_guard(Arg, [#c_clause{pats=[#c_literal{val=true}]}=Tc,Fc]) ->
[Tc#c_clause{pats=[],guard=Arg},Fc#c_clause{pats=[]}];
opt_bool_case_guard(Arg, [#c_clause{pats=[#c_literal{val=false}]}=Fc,Tc]) ->
[Tc#c_clause{pats=[],guard=Arg},Fc#c_clause{pats=[]}].
%% eval_case(Case) -> #c_case{} | #c_let{}.
%% If possible, evaluate a case at compile time. We know that the
%% last clause is guaranteed to match so if there is only one clause
%% with a pattern containing only variables then rewrite to a let.
eval_case(#c_case{arg=E,clauses=[#c_clause{pats=Ps0,
guard=#c_literal{val=true},
body=B}]}=Case, Sub) ->
Es = case cerl:is_c_values(E) of
true -> cerl:values_es(E);
false -> [E]
end,
%% Consider:
%%
%% case SomeSideEffect() of
%% X=Y -> ...
%% end
%%
%% We must not rewrite it to:
%%
%% let <X,Y> = <SomeSideEffect(),SomeSideEffect()> in ...
%%
%% because SomeSideEffect() would be evaluated twice.
%%
%% Instead we must evaluate the case expression in an outer let
%% like this:
%%
%% let NewVar = SomeSideEffect() in
%% let <X,Y> = <NewVar,NewVar> in ...
%%
Vs = make_vars([], length(Es)),
case cerl_clauses:match_list(Ps0, Vs) of
{false,_} ->
%% This can only happen if the Core Erlang code is
%% handwritten or generated by another code generator
%% than v3_core. Assuming that the Core Erlang program
%% is correct, the clause will always match at run-time.
Case;
{true,Bs} ->
eval_case_warn(B),
{Ps,As} = unzip(Bs),
InnerLet = cerl:c_let(Ps, core_lib:make_values(As), B),
Let = cerl:c_let(Vs, E, InnerLet),
expr(Let, sub_new(Sub))
end;
eval_case(Case, _) -> Case.
eval_case_warn(#c_primop{anno=Anno,
name=#c_literal{val=match_fail},
args=[_]}=Core) ->
case keyfind(eval_failure, 1, Anno) of
false ->
ok;
{eval_failure,Reason} ->
%% Example: M = not_map, M#{k:=v}
add_warning(Core, {eval_failure,Reason})
end;
eval_case_warn(_) -> ok.
%% case_opt(CaseArg, [Clause]) -> {CaseArg,[Clause]}.
%% Try and optimise a case by avoid building tuples or lists
%% in the case expression. Instead combine the variable parts
%% of the case expression to multiple "values". If a clause
%% refers to the constructed term in the case expression (which
%% was not built), introduce a let into the guard and/or body to
%% build the term.
%%
%% case {ok,[Expr1,Expr2]} of case <Expr1,Expr2> of
%% {ok,[P1,P2]} -> ... <P1,P2> -> ...
%% . ==> .
%% . .
%% . .
%% Var -> <Var1,Var2> ->
%% ... Var ... let <Var> = {ok,[Var1,Var2]}
%% in ... Var ...
%% . .
%% . .
%% . .
%% end. end.
%%
case_opt(Arg, Cs0, Sub) ->
Cs1 = [{cerl:clause_pats(C),C,[],[]} || C <- Cs0],
Args0 = case cerl:is_c_values(Arg) of
false -> [Arg];
true -> cerl:values_es(Arg)
end,
LitExpr = cerl:is_literal(Arg),
{Args,Cs2} = case_opt_args(Args0, Cs1, Sub, LitExpr, []),
Cs = [cerl:update_c_clause(C,
reverse(Ps),
letify(Bs, cerl:clause_guard(C)),
letify(Bs, cerl:clause_body(C))) ||
{[],C,Ps,Bs} <- Cs2],
{core_lib:make_values(Args),Cs}.
case_opt_args([A0|As0], Cs0, Sub, LitExpr, Acc) ->
case case_opt_arg(A0, Sub, Cs0, LitExpr) of
{error,Cs1} ->
%% Nothing to be done. Move on to the next argument.
Cs = [{Ps,C,[P|PsAcc],Bs} || {[P|Ps],C,PsAcc,Bs} <- Cs1],
case_opt_args(As0, Cs, Sub, LitExpr, [A0|Acc]);
{ok,As1,Cs} ->
%% The argument was either expanded (from tuple/list) or
%% removed (literal).
case_opt_args(As1++As0, Cs, Sub, LitExpr, Acc)
end;
case_opt_args([], Cs, _Sub, _LitExpr, Acc) ->
{reverse(Acc),Cs}.
%% case_opt_arg(Expr, Sub, Clauses0, LitExpr) ->
%% {ok,Args,Clauses} | error
%% Try to expand one argument to several arguments (if tuple/list)
%% or to remove a literal argument.
%%
case_opt_arg(E0, Sub, Cs, LitExpr) ->
case cerl:is_c_var(E0) of
false ->
case_opt_arg_1(E0, Cs, LitExpr);
true ->
case case_will_var_match(Cs) of
true ->
%% All clauses will match a variable in the
%% current position. Don't expand this variable
%% (that can only make the code worse).
{error,Cs};
false ->
%% If possible, expand this variable to a previously
%% matched term.
E = case_expand_var(E0, Sub),
case_opt_arg_1(E, Cs, LitExpr)
end
end.
case_opt_arg_1(E0, Cs0, LitExpr) ->
case cerl:is_data(E0) of
false ->
{error,Cs0};
true ->
E = case_opt_compiler_generated(E0),
Cs = case_opt_nomatch(E, Cs0, LitExpr),
case cerl:data_type(E) of
{atomic,_} ->
case_opt_lit(E, Cs);
_ ->
case_opt_data(E, Cs)
end
end.
%% case_will_var_match([Clause]) -> true | false.
%% Return if all clauses will match a variable in the
%% current position.
%%
case_will_var_match(Cs) ->
all(fun({[P|_],_,_,_}) ->
case cerl_clauses:match(P, any) of
{true,_} -> true;
_ -> false
end
end, Cs).
%% case_opt_compiler_generated(Core) -> Core'
%% Mark Core expressions as compiler generated to ensure that
%% no warnings are generated if they turn out to be unused.
%% To pretty-printed Core Erlang easier to read, don't mark
%% constructs that can't cause warnings to be emitted.
%%
case_opt_compiler_generated(Core) ->
F = fun(C) ->
case cerl:type(C) of
alias -> C;
var -> C;
_ -> cerl:set_ann(C, [compiler_generated])
end
end,
cerl_trees:map(F, Core).
%% case_expand_var(Expr0, Sub) -> Expr
%% If Expr0 is a variable that has been previously matched and
%% is known to be a tuple, return the tuple instead. Otherwise
%% return Expr0 unchanged.
%%
case_expand_var(E, #sub{t=Tdb}) ->
Key = cerl:var_name(E),
case Tdb of
#{Key:=T0} ->
case cerl:is_c_tuple(T0) of
false ->
E;
true ->
%% The pattern was a tuple. Now we must make sure
%% that the elements of the tuple are suitable. In
%% particular, we don't want binary or map
%% construction here, since that means that the
%% binary or map will be constructed in the 'case'
%% argument. That is wasteful for binaries. Even
%% worse is that any map pattern that use the ':='
%% operator will fail when used in map
%% construction (only the '=>' operator is allowed
%% when constructing a map from scratch).
try
cerl_trees:map(fun coerce_to_data/1, T0)
catch
throw:impossible ->
%% Something unsuitable was found (map or
%% or binary). Keep the variable.
E
end
end;
_ ->
E
end.
%% coerce_to_data(Core) -> Core'
%% Coerce an element originally from a pattern to an data item or or
%% variable. Throw an 'impossible' exception if non-data Core Erlang
%% terms such as binary construction or map construction are
%% encountered.
coerce_to_data(C) ->
case cerl:is_c_alias(C) of
false ->
case cerl:is_data(C) orelse cerl:is_c_var(C) of
true -> C;
false -> throw(impossible)
end;
true ->
coerce_to_data(cerl:alias_pat(C))
end.
%% case_opt_nomatch(E, Clauses, LitExpr) -> Clauses'
%% Remove all clauses that cannot possibly match.
case_opt_nomatch(E, [{[P|_],C,_,_}=Current|Cs], LitExpr) ->
case cerl_clauses:match(P, E) of
none ->
%% The pattern will not match the case expression. Remove
%% the clause. Unless the entire case expression is a
%% literal, also emit a warning.
case LitExpr of
false -> add_warning(C, nomatch_clause_type);
true -> ok
end,
case_opt_nomatch(E, Cs, LitExpr);
_ ->
[Current|case_opt_nomatch(E, Cs, LitExpr)]
end;
case_opt_nomatch(_, [], _) -> [].
%% case_opt_lit(Literal, Clauses0) -> {ok,[],Clauses} | error
%% The current part of the case expression is a literal. That
%% means that we will know at compile-time whether a clause
%% will match, and we can remove the corresponding pattern from
%% each clause.
%%
%% The only complication is if the literal is a binary or map.
%% In general, it is difficult to know whether a binary or
%% map pattern will match, so we give up in that case.
case_opt_lit(Lit, Cs0) ->
try case_opt_lit_1(Lit, Cs0) of
Cs ->
{ok,[],Cs}
catch
throw:impossible ->
{error,Cs0}
end.
case_opt_lit_1(E, [{[P|Ps],C,PsAcc,Bs0}|Cs]) ->
%% Non-matching clauses have already been removed
%% in case_opt_nomatch/3.
case cerl_clauses:match(P, E) of
{true,Bs} ->
%% The pattern matches the literal. Remove the pattern
%% and update the bindings.
[{Ps,C,PsAcc,Bs++Bs0}|case_opt_lit_1(E, Cs)];
{false,_} ->
%% Binary literal and pattern. We are not sure whether
%% the pattern will match.
throw(impossible)
end;
case_opt_lit_1(_, []) -> [].
%% case_opt_data(Expr, Clauses0, LitExpr) -> {ok,Exprs,Clauses}
%% The case expression is a non-atomic data constructor (cons
%% or tuple). We can know at compile time whether each clause
%% will match, and we can delay the building of the data to
%% the clauses where it is actually needed.
case_opt_data(E, Cs0) ->
Es = cerl:data_es(E),
TypeSig = {cerl:data_type(E),cerl:data_arity(E)},
try case_opt_data_1(Cs0, Es, TypeSig) of
Cs ->
{ok,Es,Cs}
catch
throw:impossible ->
%% The pattern contained a binary or map.
{error,Cs0}
end.
case_opt_data_1([{[P0|Ps0],C,PsAcc,Bs0}|Cs], Es, TypeSig) ->
P = case_opt_compiler_generated(P0),
BindTo = #c_var{name=dummy},
{Ps1,[{BindTo,_}|Bs1]} = case_data_pat_alias(P, BindTo, TypeSig, []),
[{Ps1++Ps0,C,PsAcc,Bs1++Bs0}|case_opt_data_1(Cs, Es, TypeSig)];
case_opt_data_1([], _, _) -> [].
case_data_pat_alias(P, BindTo0, TypeSig, Bs0) ->
case cerl:type(P) of
alias ->
%% Recursively handle the pattern and bind to
%% the alias variable.
BindTo = cerl:alias_var(P),
Apat0 = cerl:alias_pat(P),
Ann = [compiler_generated],
Apat = cerl:set_ann(Apat0, Ann),
{Ps,Bs} = case_data_pat_alias(Apat, BindTo, TypeSig, Bs0),
{Ps,[{BindTo0,BindTo}|Bs]};
var ->
%% Here we will need to actually build the data and bind
%% it to the variable.
{Type,Arity} = TypeSig,
Ann = [compiler_generated],
Vars = make_vars(Ann, Arity),
Data = cerl:ann_make_data(Ann, Type, Vars),
Bs = [{BindTo0,P},{P,Data}|Bs0],
{Vars,Bs};
_ ->
%% Since case_opt_nomatch/3 has removed all clauses that
%% cannot match, we KNOW that this clause must match and
%% that the pattern must be a data constructor.
%% Here we must build the data and bind it to the variable.
{Type,_} = TypeSig,
DataEs = cerl:data_es(P),
Vars = pat_to_expr_list(DataEs),
Ann = [compiler_generated],
Data = cerl:ann_make_data(Ann, Type, Vars),
{DataEs,[{BindTo0,Data}]}
end.
%% pat_to_expr(Pattern) -> Expression.
%% Convert a pattern to an expression if possible. We KNOW that
%% all variables in the pattern will be bound.
%%
%% Throw an 'impossible' exception if a map or (non-literal)
%% binary is encountered. Trying to use a map pattern as an
%% expression is incorrect, while rebuilding a potentially
%% huge binary in an expression would be wasteful.
pat_to_expr(P) ->
case cerl:type(P) of
alias ->
cerl:alias_var(P);
var ->
P;
_ ->
case cerl:is_data(P) of
false ->
%% Map or binary.
throw(impossible);
true ->
Es = pat_to_expr_list(cerl:data_es(P)),
cerl:update_data(P, cerl:data_type(P), Es)
end
end.
pat_to_expr_list(Ps) -> [pat_to_expr(P) || P <- Ps].
make_vars(A, Max) ->
make_vars(A, 1, Max).
make_vars(A, I, Max) when I =< Max ->
[make_var(A)|make_vars(A, I+1, Max)];
make_vars(_, _, _) -> [].
make_var(A) ->
#c_var{anno=A,name=make_var_name()}.
make_var_name() ->
N = get(new_var_num),
put(new_var_num, N+1),
list_to_atom("fol"++integer_to_list(N)).
letify(Bs, Body) ->
Ann = cerl:get_ann(Body),
foldr(fun({V,Val}, B) ->
cerl:ann_c_let(Ann, [V], Val, B)
end, Body, Bs).
%% opt_not_in_let(Let) -> Cerl
%% Try to optimize away a 'not' operator in a 'let'.
-spec opt_not_in_let(cerl:c_let()) -> cerl:cerl().
opt_not_in_let(#c_let{vars=[_]=Vs0,arg=Arg0,body=Body0}=Let) ->
case opt_not_in_let(Vs0, Arg0, Body0) of
{[],#c_values{es=[]},Body} ->
Body;
{Vs,Arg,Body} ->
Let#c_let{vars=Vs,arg=Arg,body=Body}
end;
opt_not_in_let(Let) -> Let.
%% opt_not_in_let(Vs, Arg, Body) -> {Vs',Arg',Body'}
%% Try to optimize away a 'not' operator in a 'let'.
-spec opt_not_in_let([cerl:c_var()], cerl:cerl(), cerl:cerl()) ->
{[cerl:c_var()],cerl:cerl(),cerl:cerl()}.
opt_not_in_let([#c_var{name=V}]=Vs0, Arg0, Body0) ->
case cerl:type(Body0) of
call ->
%% let <V> = Expr in not V ==>
%% let <> = <> in notExpr
case opt_not_in_let_1(V, Body0, Arg0) of
no ->
{Vs0,Arg0,Body0};
{yes,Body} ->
{[],#c_values{es=[]},Body}
end;
'let' ->
%% let <V> = Expr in let <Var> = not V in Body ==>
%% let <Var> = notExpr in Body
%% V must not be used in Body.
LetArg = cerl:let_arg(Body0),
case opt_not_in_let_1(V, LetArg, Arg0) of
no ->
{Vs0,Arg0,Body0};
{yes,Arg} ->
LetBody = cerl:let_body(Body0),
case core_lib:is_var_used(V, LetBody) of
true ->
{Vs0,Arg0,Body0};
false ->
LetVars = cerl:let_vars(Body0),
{LetVars,Arg,LetBody}
end
end;
_ ->
{Vs0,Arg0,Body0}
end;
opt_not_in_let(Vs, Arg, Body) ->
{Vs,Arg,Body}.
opt_not_in_let_1(V, Call, Body) ->
case Call of
#c_call{module=#c_literal{val=erlang},
name=#c_literal{val='not'},
args=[#c_var{name=V}]} ->
opt_not_in_let_2(Body);
_ ->
no
end.
opt_not_in_let_2(#c_case{clauses=Cs0}=Case) ->
Vars = make_vars([], 1),
Body = #c_call{module=#c_literal{val=erlang},
name=#c_literal{val='not'},
args=Vars},
Cs = [begin
Let = #c_let{vars=Vars,arg=B,body=Body},
C#c_clause{body=opt_not_in_let(Let)}
end || #c_clause{body=B}=C <- Cs0],
{yes,Case#c_case{clauses=Cs}};
opt_not_in_let_2(#c_call{}=Call0) ->
invert_call(Call0);
opt_not_in_let_2(_) -> no.
invert_call(#c_call{module=#c_literal{val=erlang},
name=#c_literal{val=Name0},
args=[_,_]}=Call) ->
case inverse_rel_op(Name0) of
no -> no;
Name -> {yes,Call#c_call{name=#c_literal{val=Name}}}
end;
invert_call(#c_call{}) -> no.
%% inverse_rel_op(Op) -> no | RevOp
inverse_rel_op('=:=') -> '=/=';
inverse_rel_op('=/=') -> '=:=';
inverse_rel_op('==') -> '/=';
inverse_rel_op('/=') -> '==';
inverse_rel_op('>') -> '=<';
inverse_rel_op('<') -> '>=';
inverse_rel_op('>=') -> '<';
inverse_rel_op('=<') -> '>';
inverse_rel_op(_) -> no.
%% opt_bool_case_in_let(LetExpr, Sub) -> Core
opt_bool_case_in_let(#c_let{vars=Vs,arg=Arg,body=B}=Let, Sub) ->
opt_case_in_let_1(Vs, Arg, B, Let, Sub).
opt_case_in_let_1([#c_var{name=V}], Arg,
#c_case{arg=#c_var{name=V}}=Case0, Let, Sub) ->
case is_simple_case_arg(Arg) of
true ->
Case = opt_bool_case(Case0#c_case{arg=Arg}),
case core_lib:is_var_used(V, Case) of
false -> expr(Case, sub_new(Sub));
true -> Let
end;
false ->
Let
end;
opt_case_in_let_1(_, _, _, Let, _) -> Let.
%% is_simple_case_arg(Expr) -> true|false
%% Determine whether the Expr is simple enough to be worth
%% substituting into a case argument. (Common substitutions
%% of variables and literals are assumed to have been already
%% handled by the caller.)
is_simple_case_arg(#c_cons{}) -> true;
is_simple_case_arg(#c_tuple{}) -> true;
is_simple_case_arg(#c_call{}) -> true;
is_simple_case_arg(#c_apply{}) -> true;
is_simple_case_arg(_) -> false.
%% is_bool_expr(Core) -> true|false
%% Check whether the Core expression is guaranteed to return
%% a boolean IF IT RETURNS AT ALL.
%%
is_bool_expr(Core) ->
is_bool_expr(Core, sub_new()).
%% is_bool_expr(Core, Sub) -> true|false
%% Check whether the Core expression is guaranteed to return
%% a boolean IF IT RETURNS AT ALL. Uses type information
%% to be able to identify more expressions as booleans.
%%
is_bool_expr(#c_call{module=#c_literal{val=erlang},
name=#c_literal{val=Name},args=Args}=Call, _) ->
NumArgs = length(Args),
erl_internal:comp_op(Name, NumArgs) orelse
erl_internal:new_type_test(Name, NumArgs) orelse
erl_internal:bool_op(Name, NumArgs) orelse
will_fail(Call);
is_bool_expr(#c_try{arg=E,vars=[#c_var{name=X}],body=#c_var{name=X},
handler=#c_literal{val=false}}, Sub) ->
is_bool_expr(E, Sub);
is_bool_expr(#c_case{clauses=Cs}, Sub) ->
is_bool_expr_list(Cs, Sub);
is_bool_expr(#c_clause{body=B}, Sub) ->
is_bool_expr(B, Sub);
is_bool_expr(#c_let{vars=[V],arg=Arg,body=B}, Sub0) ->
Sub = case is_bool_expr(Arg, Sub0) of
true -> update_types(V, [bool], Sub0);
false -> Sub0
end,
is_bool_expr(B, Sub);
is_bool_expr(#c_let{body=B}, Sub) ->
%% Binding of multiple variables.
is_bool_expr(B, Sub);
is_bool_expr(C, Sub) ->
is_boolean_type(C, Sub) =:= yes.
is_bool_expr_list([C|Cs], Sub) ->
is_bool_expr(C, Sub) andalso is_bool_expr_list(Cs, Sub);
is_bool_expr_list([], _) -> true.
%% is_safe_bool_expr(Core) -> true|false
%% Check whether the Core expression ALWAYS returns a boolean
%% (i.e. it cannot fail). Also make sure that the expression
%% is suitable for a guard (no calls to non-guard BIFs, local
%% functions, or is_record/2).
%%
is_safe_bool_expr(Core, Sub) ->
is_safe_bool_expr_1(Core, Sub, cerl_sets:new()).
is_safe_bool_expr_1(#c_call{module=#c_literal{val=erlang},
name=#c_literal{val=is_record},
args=[A,#c_literal{val=Tag},#c_literal{val=Size}]},
Sub, _BoolVars) when is_atom(Tag), is_integer(Size) ->
is_safe_simple(A, Sub);
is_safe_bool_expr_1(#c_call{module=#c_literal{val=erlang},
name=#c_literal{val=is_record}},
_Sub, _BoolVars) ->
%% The is_record/2 BIF is NOT allowed in guards.
%% The is_record/3 BIF where its second argument is not an atom or its third
%% is not an integer is NOT allowed in guards.
%%
%% NOTE: Calls like is_record(Expr, LiteralTag), where LiteralTag
%% is a literal atom referring to a defined record, have already
%% been rewritten to is_record(Expr, LiteralTag, TupleSize).
false;
is_safe_bool_expr_1(#c_call{module=#c_literal{val=erlang},
name=#c_literal{val=is_function},
args=[A,#c_literal{val=Arity}]},
Sub, _BoolVars) when is_integer(Arity), Arity >= 0 ->
is_safe_simple(A, Sub);
is_safe_bool_expr_1(#c_call{module=#c_literal{val=erlang},
name=#c_literal{val=is_function}},
_Sub, _BoolVars) ->
false;
is_safe_bool_expr_1(#c_call{module=#c_literal{val=erlang},
name=#c_literal{val=Name},args=Args},
Sub, BoolVars) ->
NumArgs = length(Args),
case (erl_internal:comp_op(Name, NumArgs) orelse
erl_internal:new_type_test(Name, NumArgs)) andalso
is_safe_simple_list(Args, Sub) of
true ->
true;
false ->
%% Boolean operators are safe if all arguments are boolean.
erl_internal:bool_op(Name, NumArgs) andalso
is_safe_bool_expr_list(Args, Sub, BoolVars)
end;
is_safe_bool_expr_1(#c_let{vars=Vars,arg=Arg,body=B}, Sub, BoolVars) ->
case is_safe_simple(Arg, Sub) of
true ->
case {is_safe_bool_expr_1(Arg, Sub, BoolVars),Vars} of
{true,[#c_var{name=V}]} ->
is_safe_bool_expr_1(B, Sub, cerl_sets:add_element(V, BoolVars));
{false,_} ->
is_safe_bool_expr_1(B, Sub, BoolVars)
end;
false -> false
end;
is_safe_bool_expr_1(#c_literal{val=Val}, _Sub, _) ->
is_boolean(Val);
is_safe_bool_expr_1(#c_var{name=V}, _Sub, BoolVars) ->
cerl_sets:is_element(V, BoolVars);
is_safe_bool_expr_1(_, _, _) -> false.
is_safe_bool_expr_list([C|Cs], Sub, BoolVars) ->
case is_safe_bool_expr_1(C, Sub, BoolVars) of
true -> is_safe_bool_expr_list(Cs, Sub, BoolVars);
false -> false
end;
is_safe_bool_expr_list([], _, _) -> true.
%% simplify_let(Let, Sub) -> Expr | impossible
%% If the argument part of an let contains a complex expression, such
%% as a let or a sequence, move the original let body into the complex
%% expression.
simplify_let(#c_let{arg=Arg0}=Let0, Sub) ->
Arg = opt_bool_case(Arg0),
Let = Let0#c_let{arg=Arg},
move_let_into_expr(Let, Arg, Sub).
move_let_into_expr(#c_let{vars=InnerVs0,body=InnerBody0}=Inner,
#c_let{vars=OuterVs0,arg=Arg0,body=OuterBody0}=Outer, Sub0) ->
%%
%% let <InnerVars> = let <OuterVars> = <Arg>
%% in <OuterBody>
%% in <InnerBody>
%%
%% ==>
%%
%% let <OuterVars> = <Arg>
%% in let <InnerVars> = <OuterBody>
%% in <InnerBody>
%%
Arg = body(Arg0, Sub0),
ScopeSub0 = sub_subst_scope(Sub0#sub{t=#{}}),
{OuterVs,ScopeSub} = pattern_list(OuterVs0, ScopeSub0),
OuterBody = body(OuterBody0, ScopeSub),
{InnerVs,Sub} = pattern_list(InnerVs0, Sub0),
InnerBody = body(InnerBody0, Sub),
Outer#c_let{vars=OuterVs,arg=Arg,
body=Inner#c_let{vars=InnerVs,arg=OuterBody,body=InnerBody}};
move_let_into_expr(#c_let{vars=Lvs0,body=Lbody0}=Let,
#c_case{arg=Cexpr0,clauses=[Ca0,Cb0|Cs]}=Case, Sub0) ->
%% Test if there are no more clauses than Ca0 and Cb0, or if
%% Cb0 is guaranteed to match.
TwoClauses = Cs =:= [] orelse
case Cb0 of
#c_clause{pats=[#c_var{}],guard=#c_literal{val=true}} -> true;
_ -> false
end,
case {TwoClauses,is_failing_clause(Ca0),is_failing_clause(Cb0)} of
{true,false,true} ->
%% let <Lvars> = case <Case-expr> of
%% <Cvars> -> <Clause-body>;
%% <OtherCvars> -> erlang:error(...)
%% end
%% in <Let-body>
%%
%% ==>
%%
%% case <Case-expr> of
%% <Cvars> ->
%% let <Lvars> = <Clause-body>
%% in <Let-body>;
%% <OtherCvars> -> erlang:error(...)
%% end
Cexpr = body(Cexpr0, Sub0),
CaVars0 = Ca0#c_clause.pats,
G0 = Ca0#c_clause.guard,
B0 = Ca0#c_clause.body,
ScopeSub0 = sub_subst_scope(Sub0#sub{t=#{}}),
{CaVars,ScopeSub} = pattern_list(CaVars0, ScopeSub0),
G = guard(G0, ScopeSub),
B1 = body(B0, ScopeSub),
{Lvs,B2,Sub1} = let_substs(Lvs0, B1, Sub0),
Sub2 = Sub1#sub{s=cerl_sets:union(ScopeSub#sub.s,
Sub1#sub.s)},
Lbody = body(Lbody0, Sub2),
B = Let#c_let{vars=Lvs,arg=core_lib:make_values(B2),body=Lbody},
Ca = Ca0#c_clause{pats=CaVars,guard=G,body=B},
Cb = clause(Cb0, Cexpr, value, Sub0),
Case#c_case{arg=Cexpr,clauses=[Ca,Cb]};
{_,_,_} -> impossible
end;
move_let_into_expr(#c_let{vars=Lvs0,body=Lbody0}=Let,
#c_seq{arg=Sarg0,body=Sbody0}=Seq, Sub0) ->
%%
%% let <Lvars> = do <Seq-arg>
%% <Seq-body>
%% in <Let-body>
%%
%% ==>
%%
%% do <Seq-arg>
%% let <Lvars> = <Seq-body>
%% in <Let-body>
%%
Sarg = body(Sarg0, Sub0),
Sbody1 = body(Sbody0, Sub0),
{Lvs,Sbody,Sub} = let_substs(Lvs0, Sbody1, Sub0),
Lbody = body(Lbody0, Sub),
Seq#c_seq{arg=Sarg,body=Let#c_let{vars=Lvs,arg=core_lib:make_values(Sbody),
body=Lbody}};
move_let_into_expr(_Let, _Expr, _Sub) -> impossible.
is_failing_clause(#c_clause{body=B}) ->
will_fail(B).
%% opt_case_in_let(Let) -> Let'
%% Try to avoid building tuples that are immediately matched.
%% A common pattern is:
%%
%% {V1,V2,...} = case E of P -> ... {Val1,Val2,...}; ... end
%%
%% In Core Erlang the pattern would look like this:
%%
%% let <V> = case E of
%% ... -> ... {Val1,Val2}
%% ...
%% end,
%% in case V of
%% {A,B} -> ... <use A and B> ...
%% end
%%
%% Rewrite this to:
%%
%% let <V1,V2> = case E of
%% ... -> ... <Val1,Val2>
%% ...
%% end,
%% in
%% let <V> = {V1,V2}
%% in case V of
%% {A,B} -> ... <use A and B> ...
%% end
%%
%% Note that the second 'case' is unchanged. The other optimizations
%% in this module will eliminate the building of the tuple and
%% rewrite the second case to:
%%
%% case <V1,V2> of
%% <A,B> -> ... <use A and B> ...
%% end
%%
opt_case_in_let(#c_let{vars=Vs,arg=Arg0,body=B}=Let0) ->
case matches_data(Vs, B) of
{yes,TypeSig} ->
case delay_build(Arg0, TypeSig) of
no ->
Let0;
{yes,Vars,Arg,Data} ->
InnerLet = Let0#c_let{arg=Data},
Let0#c_let{vars=Vars,arg=Arg,body=InnerLet}
end;
no ->
Let0
end.
matches_data([#c_var{name=V}], #c_case{arg=#c_var{name=V},
clauses=[#c_clause{pats=[P]}|_]}) ->
case cerl:is_data(P) of
false ->
no;
true ->
case cerl:data_type(P) of
{atomic,_} ->
no;
Type ->
{yes,{Type,cerl:data_arity(P)}}
end
end;
matches_data(_, _) -> no.
delay_build(Core, TypeSig) ->
case cerl:is_data(Core) of
true -> no;
false -> delay_build_1(Core, TypeSig)
end.
delay_build_1(Core0, TypeSig) ->
try delay_build_expr(Core0, TypeSig) of
Core ->
{Type,Arity} = TypeSig,
Ann = [compiler_generated],
Vars = make_vars(Ann, Arity),
Data = cerl:ann_make_data(Ann, Type, Vars),
{yes,Vars,Core,Data}
catch
throw:impossible ->
no
end.
delay_build_cs([#c_clause{body=B0}=C0|Cs], TypeSig) ->
B = delay_build_expr(B0, TypeSig),
C = C0#c_clause{body=B},
[C|delay_build_cs(Cs, TypeSig)];
delay_build_cs([], _) -> [].
delay_build_expr(Core, {Type,Arity}=TypeSig) ->
case cerl:is_data(Core) of
false ->
delay_build_expr_1(Core, TypeSig);
true ->
case {cerl:data_type(Core),cerl:data_arity(Core)} of
{Type,Arity} ->
core_lib:make_values(cerl:data_es(Core));
{_,_} ->
throw(impossible)
end
end.
delay_build_expr_1(#c_case{clauses=Cs0}=Case, TypeSig) ->
Cs = delay_build_cs(Cs0, TypeSig),
Case#c_case{clauses=Cs};
delay_build_expr_1(#c_let{body=B0}=Let, TypeSig) ->
B = delay_build_expr(B0, TypeSig),
Let#c_let{body=B};
delay_build_expr_1(#c_receive{clauses=Cs0,
timeout=Timeout,
action=A0}=Rec, TypeSig) ->
Cs = delay_build_cs(Cs0, TypeSig),
A = case Timeout of
#c_literal{val=infinity} -> A0;
_ -> delay_build_expr(A0, TypeSig)
end,
Rec#c_receive{clauses=Cs,action=A};
delay_build_expr_1(#c_seq{body=B0}=Seq, TypeSig) ->
B = delay_build_expr(B0, TypeSig),
Seq#c_seq{body=B};
delay_build_expr_1(Core, _TypeSig) ->
case will_fail(Core) of
true -> Core;
false -> throw(impossible)
end.
%% opt_simple_let(#c_let{}, Context, Sub) -> CoreTerm
%% Optimize a let construct that does not contain any lets in
%% in its argument.
opt_simple_let(Let0, Ctxt, Sub) ->
case opt_not_in_let(Let0) of
#c_let{}=Let ->
opt_simple_let_0(Let, Ctxt, Sub);
Expr ->
expr(Expr, Ctxt, Sub)
end.
opt_simple_let_0(#c_let{arg=Arg0}=Let, Ctxt, Sub) ->
Arg = body(Arg0, value, Sub), %This is a body
case will_fail(Arg) of
true -> Arg;
false -> opt_simple_let_1(Let, Arg, Ctxt, Sub)
end.
opt_simple_let_1(#c_let{vars=Vs0,body=B0}=Let, Arg0, Ctxt, Sub0) ->
%% Optimise let and add new substitutions.
{Vs1,Args,Sub1} = let_substs(Vs0, Arg0, Sub0),
BodySub = update_let_types(Vs1, Args, Sub1),
B1 = body(B0, Ctxt, BodySub),
Arg1 = core_lib:make_values(Args),
{Vs,Arg,B} = opt_not_in_let(Vs1, Arg1, B1),
opt_simple_let_2(Let, Vs, Arg, B, B0, Ctxt, Sub1).
opt_simple_let_2(Let0, Vs0, Arg0, Body, PrevBody, Ctxt, Sub) ->
case {Vs0,Arg0,Body} of
{[#c_var{name=N1}],Arg1,#c_var{name=N2}} ->
case N1 =:= N2 of
true ->
%% let <Var> = Arg in <Var> ==> Arg
Arg1;
false ->
%% let <Var> = Arg in <OtherVar> ==> seq Arg OtherVar
Arg = maybe_suppress_warnings(Arg1, Vs0, PrevBody),
expr(#c_seq{arg=Arg,body=Body}, Ctxt,
sub_new_preserve_types(Sub))
end;
{[],#c_values{es=[]},_} ->
%% No variables left.
Body;
{Vs,Arg1,#c_literal{}} ->
Arg = maybe_suppress_warnings(Arg1, Vs, PrevBody),
E = case Ctxt of
effect ->
%% Throw away the literal body.
Arg;
value ->
%% Since the variable is not used in the body, we
%% can rewrite the let to a sequence.
%% let <Var> = Arg in Literal ==> seq Arg Literal
#c_seq{arg=Arg,body=Body}
end,
expr(E, Ctxt, sub_new_preserve_types(Sub));
{Vs,Arg1,Body} ->
%% If none of the variables are used in the body, we can
%% rewrite the let to a sequence:
%% let <Var> = Arg in BodyWithoutVar ==>
%% seq Arg BodyWithoutVar
case is_any_var_used(Vs, Body) of
false ->
Arg = maybe_suppress_warnings(Arg1, Vs, PrevBody),
expr(#c_seq{arg=Arg,body=Body}, Ctxt,
sub_new_preserve_types(Sub));
true ->
Let1 = Let0#c_let{vars=Vs,arg=Arg1,body=Body},
Let2 = opt_bool_case_in_let(Let1, Sub),
opt_case_in_let_arg(Let2, Ctxt, Sub)
end
end.
%% maybe_suppress_warnings(Arg, [#c_var{}], PreviousBody) -> Arg'
%% Try to suppress false warnings when a variable is not used.
%% For instance, we don't expect a warning for useless building in:
%%
%% R = #r{}, %No warning expected.
%% R#r.f %Optimization would remove the reference to R.
%%
%% To avoid false warnings, we will check whether the variables were
%% referenced in the original unoptimized code. If they were, we will
%% consider the warning false and suppress it.
maybe_suppress_warnings(Arg, Vs, PrevBody) ->
case should_suppress_warning(Arg) of
true ->
Arg; %Already suppressed.
false ->
case is_any_var_used(Vs, PrevBody) of
true ->
suppress_warning([Arg]);
false ->
Arg
end
end.
%% Suppress warnings for a Core Erlang expression whose value will
%% be ignored.
suppress_warning([H|T]) ->
case cerl:is_literal(H) of
true ->
suppress_warning(T);
false ->
case cerl:is_data(H) of
true ->
suppress_warning(cerl:data_es(H) ++ T);
false ->
%% Some other thing, such as a function call.
%% This cannot be the compiler's fault, so the
%% warning should not be suppressed. We must
%% be careful not to destroy tail-recursion.
case T of
[] ->
H;
[_|_] ->
cerl:c_seq(H, suppress_warning(T))
end
end
end;
suppress_warning([]) -> void().
move_case_into_arg(#c_case{arg=#c_let{vars=OuterVars0,arg=OuterArg,
body=InnerArg0}=Outer,
clauses=InnerClauses}=Inner, Sub) ->
%%
%% case let <OuterVars> = <OuterArg> in <InnerArg> of
%% <InnerClauses>
%% end
%%
%% ==>
%%
%% let <OuterVars> = <OuterArg>
%% in case <InnerArg> of <InnerClauses> end
%%
ScopeSub0 = sub_subst_scope(Sub#sub{t=#{}}),
{OuterVars,ScopeSub} = pattern_list(OuterVars0, ScopeSub0),
InnerArg = body(InnerArg0, ScopeSub),
Outer#c_let{vars=OuterVars,arg=OuterArg,
body=Inner#c_case{arg=InnerArg,clauses=InnerClauses}};
move_case_into_arg(#c_case{arg=#c_case{arg=OuterArg,
clauses=[OuterCa0,OuterCb]}=Outer,
clauses=InnerClauses}=Inner0, Sub) ->
case is_failing_clause(OuterCb) of
true ->
#c_clause{pats=OuterPats0,guard=OuterGuard0,
body=InnerArg0} = OuterCa0,
%%
%% case case <OuterArg> of
%% <OuterPats> when <OuterGuard> -> <InnerArg>
%% <OuterCb>
%% ...
%% end of
%% <InnerClauses>
%% end
%%
%% ==>
%%
%% case <OuterArg> of
%% <OuterPats> when <OuterGuard> ->
%% case <InnerArg> of <InnerClauses> end
%% <OuterCb>
%% end
%%
ScopeSub0 = sub_subst_scope(Sub#sub{t=#{}}),
{OuterPats,ScopeSub} = pattern_list(OuterPats0, ScopeSub0),
OuterGuard = guard(OuterGuard0, ScopeSub),
InnerArg = body(InnerArg0, ScopeSub),
Inner = Inner0#c_case{arg=InnerArg,clauses=InnerClauses},
OuterCa = OuterCa0#c_clause{pats=OuterPats,guard=OuterGuard,
body=Inner},
Outer#c_case{arg=OuterArg,
clauses=[OuterCa,OuterCb]};
false ->
impossible
end;
move_case_into_arg(#c_case{arg=#c_seq{arg=OuterArg,body=InnerArg}=Outer,
clauses=InnerClauses}=Inner, _Sub) ->
%%
%% case do <OuterArg> <InnerArg> of
%% <InnerClauses>
%% end
%%
%% ==>
%%
%% do <OuterArg>
%% case <InnerArg> of <InerClauses> end
%%
Outer#c_seq{arg=OuterArg,
body=Inner#c_case{arg=InnerArg,clauses=InnerClauses}};
move_case_into_arg(_, _) ->
impossible.
%% In guards only, rewrite a case in a let argument like
%%
%% let <Var> = case <> of
%% <> when AnyGuard -> Literal1;
%% <> when AnyGuard -> Literal2
%% end
%% in LetBody
%%
%% to
%%
%% case <> of
%% <> when AnyGuard ->
%% let <Var> = Literal1 in LetBody
%% <> when 'true' ->
%% let <Var> = Literal2 in LetBody
%% end
%%
%% In the worst case, the size of the code could increase.
%% In practice, though, substituting the literals into
%% LetBody and doing constant folding will decrease the code
%% size. (Doing this transformation outside of guards could
%% lead to a substantational increase in code size.)
%%
opt_case_in_let_arg(#c_let{arg=#c_case{}=Case}=Let, Ctxt,
#sub{in_guard=true}=Sub) ->
opt_case_in_let_arg_1(Let, Case, Ctxt, Sub);
opt_case_in_let_arg(Let, _, _) -> Let.
opt_case_in_let_arg_1(Let0, #c_case{arg=#c_values{es=[]},
clauses=Cs}=Case0, Ctxt, Sub) ->
Let = mark_compiler_generated(Let0),
case Cs of
[#c_clause{body=#c_literal{}=BodyA}=Ca0,
#c_clause{body=#c_literal{}=BodyB}=Cb0] ->
Ca = Ca0#c_clause{body=Let#c_let{arg=BodyA}},
Cb = Cb0#c_clause{body=Let#c_let{arg=BodyB}},
Case = Case0#c_case{clauses=[Ca,Cb]},
expr(Case, Ctxt, sub_new_preserve_types(Sub));
_ -> Let
end;
opt_case_in_let_arg_1(Let, _, _, _) -> Let.
is_any_var_used([#c_var{name=V}|Vs], Expr) ->
case core_lib:is_var_used(V, Expr) of
false -> is_any_var_used(Vs, Expr);
true -> true
end;
is_any_var_used([], _) -> false.
%%%
%%% Retrieving information about types.
%%%
-spec get_type(cerl:cerl(), #sub{}) -> type_info() | 'none'.
get_type(#c_var{name=V}, #sub{t=Tdb}) ->
case Tdb of
#{V:=Type} -> Type;
_ -> none
end;
get_type(C, _) ->
case cerl:type(C) of
binary -> C;
map -> C;
_ ->
case cerl:is_data(C) of
true -> C;
false -> none
end
end.
-spec is_boolean_type(cerl:cerl(), sub()) -> yes_no_maybe().
is_boolean_type(Var, Sub) ->
case get_type(Var, Sub) of
none ->
maybe;
bool ->
yes;
C ->
B = cerl:is_c_atom(C) andalso
is_boolean(cerl:atom_val(C)),
yes_no(B)
end.
-spec is_int_type(cerl:cerl(), sub()) -> yes_no_maybe().
is_int_type(Var, Sub) ->
case get_type(Var, Sub) of
none -> maybe;
integer -> yes;
C -> yes_no(cerl:is_c_int(C))
end.
-spec is_tuple_type(cerl:cerl(), sub()) -> yes_no_maybe().
is_tuple_type(Var, Sub) ->
case get_type(Var, Sub) of
none -> maybe;
C -> yes_no(cerl:is_c_tuple(C))
end.
yes_no(true) -> yes;
yes_no(false) -> no.
%%%
%%% Update type information.
%%%
update_let_types(Vs, Args, Sub) when is_list(Args) ->
update_let_types_1(Vs, Args, Sub);
update_let_types(_Vs, _Arg, Sub) ->
%% The argument is a complex expression (such as a 'case')
%% that returns multiple values.
Sub.
update_let_types_1([#c_var{}=V|Vs], [A|As], Sub0) ->
Sub = update_types_from_expr(V, A, Sub0),
update_let_types_1(Vs, As, Sub);
update_let_types_1([], [], Sub) -> Sub.
update_types_from_expr(V, Expr, Sub) ->
Type = extract_type(Expr, Sub),
update_types(V, [Type], Sub).
extract_type(#c_call{module=#c_literal{val=erlang},
name=#c_literal{val=Name},
args=Args}=Call, Sub) ->
case returns_integer(Name, Args) of
true -> integer;
false -> extract_type_1(Call, Sub)
end;
extract_type(Expr, Sub) ->
extract_type_1(Expr, Sub).
extract_type_1(Expr, Sub) ->
case is_bool_expr(Expr, Sub) of
false -> Expr;
true -> bool
end.
returns_integer(bit_size, [_]) -> true;
returns_integer('bsl', [_,_]) -> true;
returns_integer('bsr', [_,_]) -> true;
returns_integer(byte_size, [_]) -> true;
returns_integer(length, [_]) -> true;
returns_integer('rem', [_,_]) -> true;
returns_integer(size, [_]) -> true;
returns_integer(tuple_size, [_]) -> true;
returns_integer(trunc, [_]) -> true;
returns_integer(_, _) -> false.
%% update_types(Expr, Pattern, Sub) -> Sub'
%% Update the type database.
-spec update_types(cerl:cerl(), [type_info()], sub()) -> sub().
update_types(Expr, Pat, #sub{t=Tdb0}=Sub) ->
Tdb = update_types_1(Expr, Pat, Tdb0),
Sub#sub{t=Tdb}.
update_types_1(#c_var{name=V,anno=Anno}, Pat, Types) ->
case member(reuse_for_context, Anno) of
true ->
%% If a variable has been marked for reuse of binary context,
%% optimizations based on type information are unsafe.
kill_types(V, Types);
false ->
update_types_2(V, Pat, Types)
end;
update_types_1(_, _, Types) -> Types.
update_types_2(V, [#c_tuple{}=P], Types) ->
Types#{V=>P};
update_types_2(V, [#c_literal{val=Bool}], Types) when is_boolean(Bool) ->
Types#{V=>bool};
update_types_2(V, [Type], Types) when is_atom(Type) ->
Types#{V=>Type};
update_types_2(_, _, Types) -> Types.
%% kill_types(V, Tdb) -> Tdb'
%% Kill any entries that references the variable,
%% either in the key or in the value.
kill_types(V, Tdb) ->
maps:from_list(kill_types2(V,maps:to_list(Tdb))).
kill_types2(V, [{V,_}|Tdb]) ->
kill_types2(V, Tdb);
kill_types2(V, [{_,#c_tuple{}=Tuple}=Entry|Tdb]) ->
case core_lib:is_var_used(V, Tuple) of
false -> [Entry|kill_types2(V, Tdb)];
true -> kill_types2(V, Tdb)
end;
kill_types2(V, [{_,Atom}=Entry|Tdb]) when is_atom(Atom) ->
[Entry|kill_types2(V, Tdb)];
kill_types2(_, []) -> [].
%% copy_type(DestVar, SrcVar, Tdb) -> Tdb'
%% If the SrcVar has a type, assign it to DestVar.
%%
copy_type(V, #c_var{name=Src}, Tdb) ->
case Tdb of
#{Src:=Type} -> Tdb#{V=>Type};
_ -> Tdb
end;
copy_type(_, _, Tdb) -> Tdb.
%% The atom `ok', is widely used in Erlang for "void" values.
void() -> #c_literal{val=ok}.
%%%
%%% Annotate bit syntax matching to faciliate optimization in further passes.
%%%
bsm_an(#c_case{arg=#c_var{}=V}=Case) ->
bsm_an_1([V], Case);
bsm_an(#c_case{arg=#c_values{es=Es}}=Case) ->
bsm_an_1(Es, Case);
bsm_an(Other) -> Other.
bsm_an_1(Vs, #c_case{clauses=Cs}=Case) ->
case bsm_leftmost(Cs) of
none -> Case;
Pos -> bsm_an_2(Vs, Cs, Case, Pos)
end.
bsm_an_2(Vs, Cs, Case, Pos) ->
case bsm_nonempty(Cs, Pos) of
true -> bsm_an_3(Vs, Cs, Case, Pos);
false -> Case
end.
bsm_an_3(Vs, Cs, Case, Pos) ->
try
bsm_ensure_no_partition(Cs, Pos),
bsm_do_an(Vs, Pos, Cs, Case)
catch
throw:{problem,Where,What} ->
add_bin_opt_info(Where, What),
Case
end.
bsm_do_an(Vs0, Pos, Cs0, Case) ->
case nth(Pos, Vs0) of
#c_var{name=Vname}=V0 ->
Cs = bsm_do_an_var(Vname, Pos, Cs0, []),
V = bsm_annotate_for_reuse(V0),
Bef = lists:sublist(Vs0, Pos-1),
Aft = lists:nthtail(Pos, Vs0),
case Bef ++ [V|Aft] of
[_] ->
Case#c_case{arg=V,clauses=Cs};
Vs ->
Case#c_case{arg=#c_values{es=Vs},clauses=Cs}
end;
_ ->
Case
end.
bsm_do_an_var(V, S, [#c_clause{pats=Ps,guard=G,body=B0}=C0|Cs], Acc) ->
case nth(S, Ps) of
#c_var{name=VarName} ->
case core_lib:is_var_used(V, G) of
true -> bsm_problem(C0, orig_bin_var_used_in_guard);
false -> ok
end,
case core_lib:is_var_used(VarName, G) of
true -> bsm_problem(C0, bin_var_used_in_guard);
false -> ok
end,
B1 = bsm_maybe_ctx_to_binary(VarName, B0),
B = bsm_maybe_ctx_to_binary(V, B1),
C = C0#c_clause{body=B},
bsm_do_an_var(V, S, Cs, [C|Acc]);
#c_alias{}=P ->
case bsm_could_match_binary(P) of
false ->
bsm_do_an_var(V, S, Cs, [C0|Acc]);
true ->
bsm_problem(C0, bin_opt_alias)
end;
P ->
case bsm_could_match_binary(P) andalso bsm_is_var_used(V, G, B0) of
false ->
bsm_do_an_var(V, S, Cs, [C0|Acc]);
true ->
bsm_problem(C0, bin_var_used)
end
end;
bsm_do_an_var(_, _, [], Acc) -> reverse(Acc).
bsm_annotate_for_reuse(#c_var{anno=Anno}=Var) ->
case member(reuse_for_context, Anno) of
false -> Var#c_var{anno=[reuse_for_context|Anno]};
true -> Var
end.
bsm_is_var_used(V, G, B) ->
core_lib:is_var_used(V, G) orelse core_lib:is_var_used(V, B).
bsm_maybe_ctx_to_binary(V, B) ->
case core_lib:is_var_used(V, B) andalso not previous_ctx_to_binary(V, B) of
false ->
B;
true ->
#c_seq{arg=#c_primop{name=#c_literal{val=bs_context_to_binary},
args=[#c_var{name=V}]},
body=B}
end.
previous_ctx_to_binary(V, Core) ->
case Core of
#c_seq{arg=#c_primop{name=#c_literal{val=bs_context_to_binary},
args=[#c_var{name=V}]}} ->
true;
_ ->
false
end.
%% bsm_leftmost(Cs) -> none | ArgumentNumber
%% Find the leftmost argument that does binary matching. Return
%% the number of the argument (1-N).
bsm_leftmost(Cs) ->
bsm_leftmost_1(Cs, none).
bsm_leftmost_1([#c_clause{pats=Ps}|Cs], Pos) ->
bsm_leftmost_2(Ps, Cs, 1, Pos);
bsm_leftmost_1([], Pos) -> Pos.
bsm_leftmost_2(_, Cs, Pos, Pos) ->
bsm_leftmost_1(Cs, Pos);
bsm_leftmost_2([#c_binary{}|_], Cs, N, _) ->
bsm_leftmost_1(Cs, N);
bsm_leftmost_2([_|Ps], Cs, N, Pos) ->
bsm_leftmost_2(Ps, Cs, N+1, Pos);
bsm_leftmost_2([], Cs, _, Pos) ->
bsm_leftmost_1(Cs, Pos).
%% bsm_nonempty(Cs, Pos) -> true|false
%% Check if at least one of the clauses matches a non-empty
%% binary in the given argument position.
%%
bsm_nonempty([#c_clause{pats=Ps}|Cs], Pos) ->
case nth(Pos, Ps) of
#c_binary{segments=[_|_]} ->
true;
_ ->
bsm_nonempty(Cs, Pos)
end;
bsm_nonempty([], _ ) -> false.
%% bsm_ensure_no_partition(Cs, Pos) -> ok (exception if problem)
%% We must make sure that matching is not partitioned between
%% variables like this:
%% foo(<<...>>) -> ...
%% foo(<Variable>) when ... -> ...
%% foo(<Any non-variable pattern>) ->
%% If there is such partition, we are not allowed to reuse the binary variable
%% for the match context.
%%
%% Also, arguments to the left of the argument that is matched
%% against a binary, are only allowed to be simple variables, not
%% used in guards. The reason is that we must know that the binary is
%% only matched in one place (i.e. there must be only one bs_start_match2
%% instruction emitted).
bsm_ensure_no_partition(Cs, Pos) ->
bsm_ensure_no_partition_1(Cs, Pos, before).
%% Loop through each clause.
bsm_ensure_no_partition_1([#c_clause{pats=Ps,guard=G}|Cs], Pos, State0) ->
State = bsm_ensure_no_partition_2(Ps, Pos, G, simple_vars, State0),
case State of
'after' ->
bsm_ensure_no_partition_after(Cs, Pos);
_ ->
ok
end,
bsm_ensure_no_partition_1(Cs, Pos, State);
bsm_ensure_no_partition_1([], _, _) -> ok.
%% Loop through each pattern for this clause.
bsm_ensure_no_partition_2([#c_binary{}=Where|_], 1, _, Vstate, State) ->
case State of
before when Vstate =:= simple_vars -> within;
before -> bsm_problem(Where, Vstate);
within when Vstate =:= simple_vars -> within;
within -> bsm_problem(Where, Vstate)
end;
bsm_ensure_no_partition_2([#c_alias{}=Alias|_], 1, N, Vstate, State) ->
%% Retrieve the real pattern that the alias refers to and check that.
P = bsm_real_pattern(Alias),
bsm_ensure_no_partition_2([P], 1, N, Vstate, State);
bsm_ensure_no_partition_2([_|_], 1, _, _Vstate, before=State) ->
%% No binary matching yet - therefore no partition.
State;
bsm_ensure_no_partition_2([P|_], 1, _, Vstate, State) ->
case bsm_could_match_binary(P) of
false ->
%% If clauses can be freely arranged (Vstate =:= simple_vars),
%% a clause that cannot match a binary will not partition the clause.
%% Example:
%%
%% a(Var, <<>>) -> ...
%% a(Var, []) -> ...
%% a(Var, <<B>>) -> ...
%%
%% But if the clauses can't be freely rearranged, as in
%%
%% b(Var, <<X>>) -> ...
%% b(1, 2) -> ...
%%
%% we do have a problem.
%%
case Vstate of
simple_vars -> State;
_ -> bsm_problem(P, Vstate)
end;
true ->
%% The pattern P *may* match a binary, so we must update the state.
%% (P must be a variable.)
case State of
within -> 'after';
'after' -> 'after'
end
end;
bsm_ensure_no_partition_2([#c_var{name=V}|Ps], N, G, Vstate, S) ->
case core_lib:is_var_used(V, G) of
false ->
bsm_ensure_no_partition_2(Ps, N-1, G, Vstate, S);
true ->
bsm_ensure_no_partition_2(Ps, N-1, G, bin_left_var_used_in_guard, S)
end;
bsm_ensure_no_partition_2([_|Ps], N, G, _, S) ->
bsm_ensure_no_partition_2(Ps, N-1, G, bin_argument_order, S).
bsm_ensure_no_partition_after([#c_clause{pats=Ps}=C|Cs], Pos) ->
case nth(Pos, Ps) of
#c_var{} ->
bsm_ensure_no_partition_after(Cs, Pos);
_ ->
bsm_problem(C, bin_partition)
end;
bsm_ensure_no_partition_after([], _) -> ok.
bsm_could_match_binary(#c_alias{pat=P}) -> bsm_could_match_binary(P);
bsm_could_match_binary(#c_cons{}) -> false;
bsm_could_match_binary(#c_tuple{}) -> false;
bsm_could_match_binary(#c_literal{val=Lit}) -> is_bitstring(Lit);
bsm_could_match_binary(_) -> true.
bsm_real_pattern(#c_alias{pat=P}) -> bsm_real_pattern(P);
bsm_real_pattern(P) -> P.
bsm_problem(Where, What) ->
throw({problem,Where,What}).
%%%
%%% Handling of warnings.
%%%
mark_compiler_generated(Term) ->
cerl_trees:map(fun mark_compiler_generated_1/1, Term).
mark_compiler_generated_1(#c_call{anno=Anno}=Term) ->
Term#c_call{anno=[compiler_generated|Anno--[compiler_generated]]};
mark_compiler_generated_1(Term) -> Term.
init_warnings() ->
put({?MODULE,warnings}, []).
add_bin_opt_info(Core, Term) ->
case get(bin_opt_info) of
true -> add_warning(Core, Term);
false -> ok
end.
add_warning(Core, Term) ->
case should_suppress_warning(Core) of
true ->
ok;
false ->
Anno = cerl:get_ann(Core),
Line = get_line(Anno),
File = get_file(Anno),
Key = {?MODULE,warnings},
case get(Key) of
[{File,[{Line,?MODULE,Term}]}|_] ->
ok; %We already have
%an identical warning.
Ws ->
put(Key, [{File,[{Line,?MODULE,Term}]}|Ws])
end
end.
get_line([Line|_]) when is_integer(Line) -> Line;
get_line([_|T]) -> get_line(T);
get_line([]) -> none.
get_file([{file,File}|_]) -> File;
get_file([_|T]) -> get_file(T);
get_file([]) -> "no_file". % should not happen
should_suppress_warning(Core) ->
is_compiler_generated(Core) orelse
is_result_unwanted(Core).
is_compiler_generated(Core) ->
Ann = cerl:get_ann(Core),
member(compiler_generated, Ann).
is_result_unwanted(Core) ->
Ann = cerl:get_ann(Core),
member(result_not_wanted, Ann).
get_warnings() ->
ordsets:from_list((erase({?MODULE,warnings}))).
-type error() :: 'bad_unicode' | 'bin_argument_order'
| 'bin_left_var_used_in_guard' | 'bin_opt_alias'
| 'bin_partition' | 'bin_var_used' | 'bin_var_used_in_guard'
| 'embedded_binary_size' | 'nomatch_clause_type'
| 'nomatch_guard' | 'nomatch_shadow' | 'no_clause_match'
| 'orig_bin_var_used_in_guard' | 'result_ignored'
| 'useless_building'
| {'eval_failure', term()}
| {'no_effect', {'erlang',atom(),arity()}}
| {'nomatch_shadow', integer()}
| {'embedded_unit', _, _}.
-spec format_error(error()) -> nonempty_string().
format_error({eval_failure,Reason}) ->
flatten(io_lib:format("this expression will fail with a '~p' exception", [Reason]));
format_error(embedded_binary_size) ->
"binary construction will fail with a 'badarg' exception "
"(field size for binary/bitstring greater than actual size)";
format_error({embedded_unit,Unit,Size}) ->
M = io_lib:format("binary construction will fail with a 'badarg' exception "
"(size ~p cannot be evenly divided by unit ~p)", [Size,Unit]),
flatten(M);
format_error(bad_unicode) ->
"binary construction will fail with a 'badarg' exception "
"(invalid Unicode code point in a utf8/utf16/utf32 segment)";
format_error({nomatch_shadow,Line}) ->
M = io_lib:format("this clause cannot match because a previous clause at line ~p "
"always matches", [Line]),
flatten(M);
format_error(nomatch_shadow) ->
"this clause cannot match because a previous clause always matches";
format_error(nomatch_guard) ->
"the guard for this clause evaluates to 'false'";
format_error(no_clause_match) ->
"no clause will ever match";
format_error(nomatch_clause_type) ->
"this clause cannot match because of different types/sizes";
format_error({no_effect,{erlang,F,A}}) ->
{Fmt,Args} = case erl_internal:comp_op(F, A) of
true ->
{"use of operator ~p has no effect",[F]};
false ->
case erl_internal:bif(F, A) of
false ->
{"the call to erlang:~p/~p has no effect",[F,A]};
true ->
{"the call to ~p/~p has no effect",[F,A]}
end
end,
flatten(io_lib:format(Fmt, Args));
format_error(result_ignored) ->
"the result of the expression is ignored "
"(suppress the warning by assigning the expression to the _ variable)";
format_error(useless_building) ->
"a term is constructed, but never used";
format_error(bin_opt_alias) ->
"INFO: the '=' operator will prevent delayed sub binary optimization";
format_error(bin_partition) ->
"INFO: matching non-variables after a previous clause matching a variable "
"will prevent delayed sub binary optimization";
format_error(bin_left_var_used_in_guard) ->
"INFO: a variable to the left of the binary pattern is used in a guard; "
"will prevent delayed sub binary optimization";
format_error(bin_argument_order) ->
"INFO: matching anything else but a plain variable to the left of "
"binary pattern will prevent delayed sub binary optimization; "
"SUGGEST changing argument order";
format_error(bin_var_used) ->
"INFO: using a matched out sub binary will prevent "
"delayed sub binary optimization";
format_error(orig_bin_var_used_in_guard) ->
"INFO: using the original binary variable in a guard will prevent "
"delayed sub binary optimization";
format_error(bin_var_used_in_guard) ->
"INFO: using a matched out sub binary in a guard will prevent "
"delayed sub binary optimization".
-ifdef(DEBUG).
%% In order for simplify_let/2 to work correctly, the list of
%% in-scope variables must always be a superset of the free variables
%% in the current expression (otherwise we might fail to rename a variable
%% when needed and get a name capture bug).
verify_scope(E, #sub{s=Scope}) ->
Free0 = cerl_trees:free_variables(E),
Free = [V || V <- Free0, not is_tuple(V)], %Ignore function names.
case ordsets:is_subset(Free, cerl_sets:to_list(Scope)) of
true -> true;
false ->
io:format("~p\n", [E]),
io:format("~p\n", [Free]),
io:format("~p\n", [cerl_sets:to_list(Scope)]),
false
end.
-endif.
