Optimise creation of anonymous functions

This introduces a similar optimisation for normal funs
to what was introduced for external funs in #1725.
It is possible to allocate the fun as a literal, if it does not capture
the environment (i.e. it does not close over any variables).
Unfortunately it's not possible to do this in the compiler due to
problems with representation of such functions in the `.beam` files.
Fortunately, we can do this in the loader.

Simple evaluation shows that functions that don't capture the
enviornment consistute over 60% of all funs in the source code of
Erlang/OTP itself.

The only downside is that we lose a meningful value in the `pid` field
of the fun. The goal of this field, beyond debugging, was to be
able to identify the original node of a function. To be able to still do
this, the functions that are created in the loader are assigned the init
pid as the creator.

To solve issues with staryp, initially set the `erts_init_process_id`
to `ERTS_INVALID_PID` and skip the described optimisation if the value
is still uninitialised.

9 files changed, 91 insertions, 27 deletions

diff --git a/erts/doc/src/erlang.xml b/erts/doc/src/erlang.xml
index 15bd80e72f..be8918c158 100644
--- a/erts/doc/src/erlang.xml
+++ b/erts/doc/src/erlang.xml
@@ -1742,6 +1742,10 @@ true</pre>
           <item>
             <p><c>Pid</c> is the process identifier of the process
               that originally created the fun.</p>
+            <p>It might point to the <c>init</c> process if the
+              <c>Fun</c> was statically allocated when module was
+              loaded (this optimisation is performed for local
+              functions that do not capture the enviornment).</p>
           </item>
           <tag><c>{index, Index}</c></tag>
           <item>
diff --git a/erts/emulator/beam/beam_load.c b/erts/emulator/beam/beam_load.c
index e61199a8fd..50cbb37f3e 100644
--- a/erts/emulator/beam/beam_load.c
+++ b/erts/emulator/beam/beam_load.c
@@ -4245,21 +4245,55 @@ gen_make_fun2(LoaderState* stp, GenOpArg idx)
 {
     ErlFunEntry* fe;
     GenOp* op;
+    Uint arity, num_free;
 
     if (idx.val >= stp->num_lambdas) {
-	stp->lambda_error = "missing or short chunk 'FunT'";
-	fe = 0;
+        stp->lambda_error = "missing or short chunk 'FunT'";
+        fe = 0;
+        num_free = 0;
+        arity = 0;
     } else {
-	fe = stp->lambdas[idx.val].fe;
+        fe = stp->lambdas[idx.val].fe;
+        num_free = stp->lambdas[idx.val].num_free;
+        arity = fe->arity;
     }
 
     NEW_GENOP(stp, op);
-    op->op = genop_i_make_fun_2;
-    op->arity = 2;
-    op->a[0].type = TAG_u;
-    op->a[0].val = (BeamInstr) fe;
-    op->a[1].type = TAG_u;
-    op->a[1].val = stp->lambdas[idx.val].num_free;
+
+    /*
+     * It's possible this is called before init process is started,
+     * skip the optimisation in such case.
+     */
+    if (num_free == 0 && erts_init_process_id != ERTS_INVALID_PID) {
+        Uint lit;
+        Eterm* hp;
+        ErlFunThing* funp;
+
+        lit = new_literal(stp, &hp, ERL_FUN_SIZE);
+        funp = (ErlFunThing *) hp;
+        erts_refc_inc(&fe->refc, 2);
+        funp->thing_word = HEADER_FUN;
+        funp->next = NULL;
+        funp->fe = fe;
+        funp->num_free = 0;
+        funp->creator = erts_init_process_id;
+        funp->arity = arity;
+
+        op->op = genop_move_2;
+        op->arity = 2;
+        op->a[0].type = TAG_q;
+        op->a[0].val = lit;
+        op->a[1].type = TAG_x;
+        op->a[1].val = 0;
+    } else {
+        op->op = genop_i_make_fun_2;
+        op->arity = 2;
+        op->a[0].type = TAG_u;
+        op->a[0].val = (BeamInstr) fe;
+        op->a[1].type = TAG_u;
+        op->a[1].val = num_free;
+    }
+
     op->next = NULL;
     return op;
 }
diff --git a/erts/emulator/beam/break.c b/erts/emulator/beam/break.c
index 9ff52c92b8..81531f6cc8 100644
--- a/erts/emulator/beam/break.c
+++ b/erts/emulator/beam/break.c
@@ -108,6 +108,7 @@ process_killer(void)
 		    erts_exit(0, "");
 		switch(j) {
 		case 'k':
+                    ASSERT(erts_init_process_id != ERTS_INVALID_PID);
                     /* Send a 'kill' exit signal from init process */
                     erts_proc_sig_send_exit(NULL, erts_init_process_id,
                                             rp->common.id, am_kill, NIL,
diff --git a/erts/emulator/beam/erl_init.c b/erts/emulator/beam/erl_init.c
index 57c6c10c7f..5da7b43b9e 100644
--- a/erts/emulator/beam/erl_init.c
+++ b/erts/emulator/beam/erl_init.c
@@ -128,7 +128,7 @@ const Eterm etp_hole_marker = 0;
 
 static int modified_sched_thread_suggested_stack_size = 0;
 
-Eterm erts_init_process_id;
+Eterm erts_init_process_id = ERTS_INVALID_PID;
 
 /*
  * Note about VxWorks: All variables must be initialized by executable code,
@@ -2258,6 +2258,7 @@ erl_start(int argc, char **argv)
 
     erts_init_process_id = erl_first_process_otp("otp_ring0", NULL, 0,
                                                  boot_argc, boot_argv);
+	ASSERT(erts_init_process_id != ERTS_INVALID_PID);
 
     {
 	/*
diff --git a/erts/emulator/beam/erl_process_dump.c b/erts/emulator/beam/erl_process_dump.c
index 243db4c734..706530023b 100644
--- a/erts/emulator/beam/erl_process_dump.c
+++ b/erts/emulator/beam/erl_process_dump.c
@@ -963,12 +963,16 @@ dump_module_literals(fmtfn_t to, void *to_arg, ErtsLiteralArea* lit_area)
                     }
                     erts_putc(to, to_arg, '\n');
                 }
-            } else if (is_export_header(w)) {
+            } else if (is_export_header(w) || is_fun_header(w)) {
                 dump_externally(to, to_arg, term);
                 erts_putc(to, to_arg, '\n');
             }
             size = 1 + header_arity(w);
             switch (w & _HEADER_SUBTAG_MASK) {
+            case FUN_SUBTAG:
+                ASSERT(((ErlFunThing*)(htop))->num_free == 0);
+                size += 1;
+                break;
             case MAP_SUBTAG:
                 if (is_flatmap_header(w)) {
                     size += 1 + flatmap_get_size(htop);
diff --git a/erts/emulator/test/code_SUITE.erl b/erts/emulator/test/code_SUITE.erl
index 9c6dc3ff83..7e690fd870 100644
--- a/erts/emulator/test/code_SUITE.erl
+++ b/erts/emulator/test/code_SUITE.erl
@@ -332,6 +332,7 @@ constant_pools(Config) when is_list(Config) ->
     A = literals:a(),
     B = literals:b(),
     C = literals:huge_bignum(),
+    D = literals:funs(),
     process_flag(trap_exit, true),
     Self = self(),
 
@@ -345,7 +346,7 @@ constant_pools(Config) when is_list(Config) ->
     true = erlang:purge_module(literals),
     NoOldHeap ! done,
     receive
-        {'EXIT',NoOldHeap,{A,B,C}} ->
+        {'EXIT',NoOldHeap,{A,B,C,D}} ->
             ok;
         Other ->
             ct:fail({unexpected,Other})
@@ -362,7 +363,7 @@ constant_pools(Config) when is_list(Config) ->
     erlang:purge_module(literals),
     OldHeap ! done,
     receive
-	{'EXIT',OldHeap,{A,B,C,[1,2,3|_]=Seq}} when length(Seq) =:= 16 ->
+	{'EXIT',OldHeap,{A,B,C,D,[1,2,3|_]=Seq}} when length(Seq) =:= 16 ->
 	    ok
     end,
 
@@ -390,7 +391,7 @@ constant_pools(Config) when is_list(Config) ->
 	{'DOWN', Mon, process, Hib, Reason} ->
 	    {undef, [{no_module,
 		      no_function,
-		      [{A,B,C,[1,2,3|_]=Seq}], _}]} = Reason,
+		      [{A,B,C,D,[1,2,3|_]=Seq}], _}]} = Reason,
 	    16 = length(Seq)
     end,
     HeapSz = TotHeapSz, %% Ensure restored to hibernated state...
@@ -400,7 +401,9 @@ constant_pools(Config) when is_list(Config) ->
 no_old_heap(Parent) ->
     A = literals:a(),
     B = literals:b(),
-    Res = {A,B,literals:huge_bignum()},
+    C = literals:huge_bignum(),
+    D = literals:funs(),
+    Res = {A,B,C,D},
     Parent ! go,
     receive
         done ->
@@ -410,7 +413,9 @@ no_old_heap(Parent) ->
 old_heap(Parent) ->
     A = literals:a(),
     B = literals:b(),
-    Res = {A,B,literals:huge_bignum(),lists:seq(1, 16)},
+    C = literals:huge_bignum(),
+    D = literals:funs(),
+    Res = {A,B,C,D,lists:seq(1, 16)},
     create_old_heap(),
     Parent ! go,
     receive
@@ -421,7 +426,9 @@ old_heap(Parent) ->
 hibernated(Parent) ->
     A = literals:a(),
     B = literals:b(),
-    Res = {A,B,literals:huge_bignum(),lists:seq(1, 16)},
+    C = literals:huge_bignum(),
+    D = literals:funs(),
+    Res = {A,B,C,D,lists:seq(1, 16)},
     Parent ! go,
     erlang:hibernate(no_module, no_function, [Res]).
 
@@ -755,7 +762,8 @@ t_copy_literals_frags(Config) when is_list(Config) ->
                                           0, 1, 2, 3, 4, 5, 6, 7,
                                           8, 9,10,11,12,13,14,15,
                                           0, 1, 2, 3, 4, 5, 6, 7,
-                                          8, 9,10,11,12,13,14,15>>}]),
+                                          8, 9,10,11,12,13,14,15>>},
+                        {f, fun ?MODULE:all/0}]),
 
     {module, ?mod} = erlang:load_module(?mod, Bin),
     N = 6000,
@@ -796,6 +804,7 @@ literal_receiver() ->
             C = ?mod:c(),
             D = ?mod:d(),
             E = ?mod:e(),
+            F = ?mod:f(),
             literal_receiver();
         {Pid, sender_confirm} ->
             io:format("sender confirm ~w~n", [Pid]),
@@ -811,7 +820,8 @@ literal_sender(N, Recv) ->
                           ?mod:b(),
                           ?mod:c(),
                           ?mod:d(),
-                          ?mod:e()]},
+                          ?mod:e(),
+                          ?mod:f()]},
     literal_sender(N - 1, Recv).
 
 literal_switcher() ->
diff --git a/erts/emulator/test/code_SUITE_data/literals.erl b/erts/emulator/test/code_SUITE_data/literals.erl
index 7c3b0ebe73..13c8b412b0 100644
--- a/erts/emulator/test/code_SUITE_data/literals.erl
+++ b/erts/emulator/test/code_SUITE_data/literals.erl
@@ -19,7 +19,8 @@
 %%
 
 -module(literals).
--export([a/0,b/0,huge_bignum/0,binary/0,unused_binaries/0,bits/0]).
+-export([a/0,b/0,huge_bignum/0,funs/0,
+         binary/0,unused_binaries/0,bits/0]).
 -export([msg1/0,msg2/0,msg3/0,msg4/0,msg5/0]).
 
 a() ->
@@ -108,3 +109,8 @@ msg2() -> {"hello","world"}.
 msg3() -> <<"halloj">>.
 msg4() -> #{ 1=> "hello", b => "world"}.
 msg5() -> {1,2,3,4,5,6}.
+
+funs() ->
+    %% Literal funs (in a non-literal list).
+    [fun ?MODULE:a/0,
+     fun() -> ok end].                          %No environment.
diff --git a/erts/emulator/test/fun_SUITE.erl b/erts/emulator/test/fun_SUITE.erl
index 7d29ebec52..6730003b58 100644
--- a/erts/emulator/test/fun_SUITE.erl
+++ b/erts/emulator/test/fun_SUITE.erl
@@ -576,7 +576,7 @@ refc_dist(Config) when is_list(Config) ->
     process_flag(trap_exit, true),
     Pid = spawn_link(Node, fun() -> receive
                                         Fun when is_function(Fun) ->
-                                            2 = fun_refc(Fun),
+                                            3 = fun_refc(Fun),
                                             exit({normal,Fun}) end
                            end),
     F = fun() -> 42 end,
@@ -598,7 +598,7 @@ refc_dist_send(Node, F) ->
     Pid = spawn_link(Node, fun() -> receive
                                         {To,Fun} when is_function(Fun) ->
                                             wait_until(fun () ->
-                                                               2 =:= fun_refc(Fun)
+                                                               3 =:= fun_refc(Fun)
                                                        end),
                                             To ! Fun
                                     end
@@ -626,7 +626,7 @@ refc_dist_reg_send(Node, F) ->
                                    Me ! Ref,
                                    receive
                                        {Me,Fun} when is_function(Fun) ->
-                                           2 = fun_refc(Fun),
+                                           3 = fun_refc(Fun),
                                            Me ! Fun
                                    end
                            end),
@@ -806,11 +806,13 @@ verify_not_undef(Fun, Tag) ->
 	    ct:fail("tag ~w not defined in fun_info", [Tag]);
 	{Tag,_} -> ok
     end.
-	    
+
 id(X) ->
     X.
 
 spawn_call(Node, AFun) ->
+    Parent = self(),
+    Init = erlang:whereis(init),
     Pid = spawn_link(Node,
 		     fun() ->
 			     receive
@@ -821,8 +823,10 @@ spawn_call(Node, AFun) ->
 						_ -> lists:seq(0, Arity-1)
 					    end,
 				     Res = apply(Fun, Args),
-				     {pid,Creator} = erlang:fun_info(Fun, pid),
-				     Creator ! {result,Res}
+                     case erlang:fun_info(Fun, pid) of
+                        {pid,Init} -> Parent ! {result,Res};
+                        {pid,Creator} -> Creator ! {result,Res}
+                     end
 			     end
 		     end),
     Pid ! {AFun,AFun,AFun},
diff --git a/lib/stdlib/test/lists_SUITE.erl b/lib/stdlib/test/lists_SUITE.erl
index 837ab4e97e..af94fc79bc 100644
--- a/lib/stdlib/test/lists_SUITE.erl
+++ b/lib/stdlib/test/lists_SUITE.erl
@@ -1679,7 +1679,7 @@ make_fun() ->
     receive {Pid, Fun} -> Fun end.
 
 make_fun(Pid) ->
-    Pid ! {self(), fun make_fun/1}.
+    Pid ! {self(), fun (X) -> {X, Pid} end}.
 
 fun_pid(Fun) ->
     erlang:fun_info(Fun, pid).