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0407-Fix-side-effect-optimization-when-compilin...
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File 0407-Fix-side-effect-optimization-when-compiling-from-Cor.patch of Package erlang
From a2b94643d345505bcee103b114147e3cb962b8ac Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?John=20H=C3=B6gberg?= <john@erlang.org> Date: Mon, 16 Jul 2018 15:21:04 +0200 Subject: [PATCH] Fix side-effect optimization when compiling from Core Erlang MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit When an expression is only used for its side effects, we try to remove everything that doesn't tie into a side-effect, but we went a bit too far when we applied the optimization to funs defined in such a context. Consider the following: do letrec 'f'/0 = fun () -> ... whatever ... in call 'side':'effect'(apply 'f'/0()) 'ok' When f/0 is optimized under the assumption that its return value is unused, side:effect/1 will be fed the result of the last side-effecting expression in f/0 instead of its actual result. https://bugs.erlang.org/browse/ERL-658 Co-authored-by: Björn Gustavsson <bjorn@erlang.org> --- lib/compiler/src/sys_core_fold.erl | 87 +++++++++++++++++++++- lib/compiler/test/core_SUITE.erl | 5 +- .../test/core_SUITE_data/fun_letrec_effect.core | 25 +++++++ lib/compiler/test/core_fold_SUITE.erl | 24 +++++- 4 files changed, 136 insertions(+), 5 deletions(-) create mode 100644 lib/compiler/test/core_SUITE_data/fun_letrec_effect.core diff --git a/lib/compiler/src/sys_core_fold.erl b/lib/compiler/src/sys_core_fold.erl index ceb7d56221..0e4f2d5cb8 100644 --- a/lib/compiler/src/sys_core_fold.erl +++ b/lib/compiler/src/sys_core_fold.erl @@ -352,7 +352,12 @@ expr(#c_letrec{body=#c_var{}}=Letrec, effect, _Sub) -> void(); expr(#c_letrec{defs=Fs0,body=B0}=Letrec, Ctxt, Sub) -> Fs1 = map(fun ({Name,Fb}) -> - {Name,expr(Fb, {letrec,Ctxt}, Sub)} + case Ctxt =:= effect andalso is_fun_effect_safe(Name, B0) of + true -> + {Name,expr(Fb, {letrec, effect}, Sub)}; + false -> + {Name,expr(Fb, {letrec, value}, Sub)} + end end, Fs0), B1 = body(B0, Ctxt, Sub), Letrec#c_letrec{defs=Fs1,body=B1}; @@ -483,6 +488,86 @@ expr(#c_try{anno=A,arg=E0,vars=Vs0,body=B0,evars=Evs0,handler=H0}=Try, _, Sub0) Try#c_try{arg=E1,vars=Vs1,body=B1,evars=Evs1,handler=H1} end. + +%% If a fun or its application is used as an argument, then it's unsafe to +%% handle it in effect context as the side-effects may rely on its return +%% value. The following is a minimal example of where it can go wrong: +%% +%% do letrec 'f'/0 = fun () -> ... whatever ... +%% in call 'side':'effect'(apply 'f'/0()) +%% 'ok' +%% +%% This function returns 'true' if Body definitely does not rely on a +%% value produced by FVar, or 'false' if Body depends on or might depend on +%% a value produced by FVar. + +is_fun_effect_safe(#c_var{}=FVar, Body) -> + ifes_1(FVar, Body, true). + +ifes_1(FVar, #c_alias{pat=Pat}, _Safe) -> + ifes_1(FVar, Pat, false); +ifes_1(FVar, #c_apply{op=Op,args=Args}, Safe) -> + %% FVar(...) is safe as long its return value is ignored, but it's never + %% okay to pass FVar as an argument. + ifes_list(FVar, Args, false) andalso ifes_1(FVar, Op, Safe); +ifes_1(FVar, #c_binary{segments=Segments}, _Safe) -> + ifes_list(FVar, Segments, false); +ifes_1(FVar, #c_bitstr{val=Val,size=Size,unit=Unit}, _Safe) -> + ifes_list(FVar, [Val, Size, Unit], false); +ifes_1(FVar, #c_call{args=Args}, _Safe) -> + ifes_list(FVar, Args, false); +ifes_1(FVar, #c_case{arg=Arg,clauses=Clauses}, Safe) -> + ifes_1(FVar, Arg, false) andalso ifes_list(FVar, Clauses, Safe); +ifes_1(FVar, #c_catch{body=Body}, _Safe) -> + ifes_1(FVar, Body, false); +ifes_1(FVar, #c_clause{pats=Pats,guard=Guard,body=Body}, Safe) -> + ifes_list(FVar, Pats, false) andalso + ifes_1(FVar, Guard, false) andalso + ifes_1(FVar, Body, Safe); +ifes_1(FVar, #c_cons{hd=Hd,tl=Tl}, _Safe) -> + ifes_1(FVar, Hd, false) andalso ifes_1(FVar, Tl, false); +ifes_1(FVar, #c_fun{body=Body}, _Safe) -> + ifes_1(FVar, Body, false); +ifes_1(FVar, #c_let{arg=Arg,body=Body}, Safe) -> + ifes_1(FVar, Arg, false) andalso ifes_1(FVar, Body, Safe); +ifes_1(FVar, #c_letrec{defs=Defs,body=Body}, Safe) -> + Funs = [Fun || {_,Fun} <- Defs], + ifes_list(FVar, Funs, false) andalso ifes_1(FVar, Body, Safe); +ifes_1(_FVar, #c_literal{}, _Safe) -> + true; +ifes_1(FVar, #c_map{arg=Arg,es=Elements}, _Safe) -> + ifes_1(FVar, Arg, false) andalso ifes_list(FVar, Elements, false); +ifes_1(FVar, #c_map_pair{key=Key,val=Val}, _Safe) -> + ifes_1(FVar, Key, false) andalso ifes_1(FVar, Val, false); +ifes_1(FVar, #c_primop{args=Args}, _Safe) -> + ifes_list(FVar, Args, false); +ifes_1(FVar, #c_receive{timeout=Timeout,action=Action,clauses=Clauses}, Safe) -> + ifes_1(FVar, Timeout, false) andalso + ifes_1(FVar, Action, Safe) andalso + ifes_list(FVar, Clauses, Safe); +ifes_1(FVar, #c_seq{arg=Arg,body=Body}, Safe) -> + %% Arg of a #c_seq{} has no effect so it's okay to use FVar there even if + %% Safe=false. + ifes_1(FVar, Arg, true) andalso ifes_1(FVar, Body, Safe); +ifes_1(FVar, #c_try{arg=Arg,handler=Handler,body=Body}, Safe) -> + ifes_1(FVar, Arg, false) andalso + ifes_1(FVar, Handler, Safe) andalso + ifes_1(FVar, Body, Safe); +ifes_1(FVar, #c_tuple{es=Elements}, _Safe) -> + ifes_list(FVar, Elements, false); +ifes_1(FVar, #c_values{es=Elements}, _Safe) -> + ifes_list(FVar, Elements, false); +ifes_1(#c_var{name=Name}, #c_var{name=Name}, Safe) -> + %% It's safe to return FVar if it's unused. + Safe; +ifes_1(_FVar, #c_var{}, _Safe) -> + true. + +ifes_list(FVar, [E|Es], Safe) -> + ifes_1(FVar, E, Safe) andalso ifes_list(FVar, Es, Safe); +ifes_list(_FVar, [], _Safe) -> + true. + expr_list(Es, Ctxt, Sub) -> [expr(E, Ctxt, Sub) || E <- Es]. diff --git a/lib/compiler/test/core_SUITE.erl b/lib/compiler/test/core_SUITE.erl index 23f420f5f2..e5611e99d1 100644 --- a/lib/compiler/test/core_SUITE.erl +++ b/lib/compiler/test/core_SUITE.erl @@ -27,7 +27,7 @@ unsafe_case/1,nomatch_shadow/1,reversed_annos/1, map_core_test/1,eval_case/1,bad_boolean_guard/1, bs_shadowed_size_var/1, - name_capture/1 + name_capture/1, fun_letrec_effect/1 ]). -include_lib("common_test/include/ct.hrl"). @@ -55,7 +55,7 @@ groups() -> eval_is_boolean,unsafe_case,nomatch_shadow,reversed_annos, map_core_test,eval_case,bad_boolean_guard, bs_shadowed_size_var, - name_capture + name_capture, fun_letrec_effect ]}]. @@ -85,6 +85,7 @@ end_per_group(_GroupName, Config) -> ?comp(bad_boolean_guard). ?comp(bs_shadowed_size_var). ?comp(name_capture). +?comp(fun_letrec_effect). try_it(Mod, Conf) -> Src = filename:join(proplists:get_value(data_dir, Conf), diff --git a/lib/compiler/test/core_SUITE_data/fun_letrec_effect.core b/lib/compiler/test/core_SUITE_data/fun_letrec_effect.core new file mode 100644 index 0000000000..ab6f5b7940 --- /dev/null +++ b/lib/compiler/test/core_SUITE_data/fun_letrec_effect.core @@ -0,0 +1,25 @@ +module 'fun_letrec_effect' ['fun_letrec_effect'/0, 'ok'/0, 'wat'/0] +attributes [] + +'fun_letrec_effect'/0 = + fun () -> + do apply 'wat'/0() + receive + <'bar'> when 'true' -> 'ok' + <_0> when 'true' -> 'failed' + after 'infinity' -> + 'true' + +%% The return value (bar) of the fun was optimized away because the result of +%% the `letrec ... in` was unused, despite the fun's return value being +%% relevant for the side-effect of the expression. +'wat'/0 = + fun () -> + let <Self> = call 'erlang':'self'() in + do letrec 'f'/0 = fun () -> + do call 'maps':'put'('foo', 'bar', ~{}~) + 'bar' + in call 'erlang':'send'(Self, apply 'f'/0()) + 'undefined' + +end diff --git a/lib/compiler/test/core_fold_SUITE.erl b/lib/compiler/test/core_fold_SUITE.erl index 2a2369fff9..47606014c3 100644 --- a/lib/compiler/test/core_fold_SUITE.erl +++ b/lib/compiler/test/core_fold_SUITE.erl @@ -26,7 +26,7 @@ unused_multiple_values_error/1,unused_multiple_values/1, multiple_aliases/1,redundant_boolean_clauses/1, mixed_matching_clauses/1,unnecessary_building/1, - no_no_file/1,configuration/1]). + no_no_file/1,configuration/1,cover_letrec_effect/1]). -export([foo/0,foo/1,foo/2,foo/3]). @@ -45,7 +45,7 @@ groups() -> unused_multiple_values_error,unused_multiple_values, multiple_aliases,redundant_boolean_clauses, mixed_matching_clauses,unnecessary_building, - no_no_file,configuration]}]. + no_no_file,configuration,cover_letrec_effect]}]. init_per_suite(Config) -> @@ -528,4 +528,25 @@ empty_values(_Config) -> art() -> creating. +cover_letrec_effect(_Config) -> + self() ! {tag,42}, + _ = try + try + ignore + after + receive + {tag,Int}=Term -> + Res = #{k => {Term,<<Int:16>>}}, + self() ! Res + end + end + after + ok + end, + receive + Any -> + #{k := {{tag,42},<<42:16>>}} = Any + end, + ok. + id(I) -> I. -- 2.16.4
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