Compile external fun expressions to literals

The expressions fun M:F/A, when all elements are literals are also
treated as a literal. Since they have consistent representation and
don't depend on the code currently loaded in the VM, this is safe.
This can provide significant performance improvements in code using such
functions extensively - a full function call to erlang:make_fun/3 is
replaced by a single move instruction and no register shuffling or
saving registers to stack is necessary. Additionally, compound data
types that contain such external functions as elements can be treated as
literals too.

The commit also changes the representation of external funs to be a
valid Erlang syntax and adds support for literal external funs to core
Erlang.

4 files changed, 57 insertions, 21 deletions

diff --git a/erts/emulator/beam/beam_load.c b/erts/emulator/beam/beam_load.c
index e242fe9140..3ac98cec8d 100644
--- a/erts/emulator/beam/beam_load.c
+++ b/erts/emulator/beam/beam_load.c
@@ -4521,6 +4521,19 @@ is_empty_map(LoaderState* stp, GenOpArg Lit)
 }
 
 /*
+ * Predicate to test whether the given literal is an export.
+ */
+static int
+literal_is_export(LoaderState* stp, GenOpArg Lit)
+{
+    Eterm term;
+
+    ASSERT(Lit.type == TAG_q);
+    term = stp->literals[Lit.val].term;
+    return is_export(term);
+}
+
+/*
  * Pseudo predicate map_key_sort that will sort the Rest operand for
  * map instructions as a side effect.
  */
diff --git a/erts/emulator/beam/erl_printf_term.c b/erts/emulator/beam/erl_printf_term.c
index e6f8460164..910f241a3a 100644
--- a/erts/emulator/beam/erl_printf_term.c
+++ b/erts/emulator/beam/erl_printf_term.c
@@ -532,14 +532,13 @@ print_term(fmtfn_t fn, void* arg, Eterm obj, long *dcount) {
 		Atom* module = atom_tab(atom_val(ep->info.mfa.module));
 		Atom* name = atom_tab(atom_val(ep->info.mfa.function));
 
-		PRINT_STRING(res, fn, arg, "#Fun<");
+		PRINT_STRING(res, fn, arg, "fun ");
 		PRINT_BUF(res, fn, arg, module->name, module->len);
-		PRINT_CHAR(res, fn, arg, '.');
+		PRINT_CHAR(res, fn, arg, ':');
 		PRINT_BUF(res, fn, arg, name->name, name->len);
-		PRINT_CHAR(res, fn, arg, '.');
+		PRINT_CHAR(res, fn, arg, '/');
 		PRINT_SWORD(res, fn, arg, 'd', 0, 1,
 			    (ErlPfSWord) ep->info.mfa.arity);
-		PRINT_CHAR(res, fn, arg, '>');
 	    }
 	    break;
 	case FUN_DEF:
diff --git a/erts/emulator/beam/ops.tab b/erts/emulator/beam/ops.tab
index 77e375f2c0..6e03f39d97 100644
--- a/erts/emulator/beam/ops.tab
+++ b/erts/emulator/beam/ops.tab
@@ -710,7 +710,8 @@ is_boolean Fail=f ac => jump Fail
 is_boolean f? xy
 %hot
 
-is_function2 Fail=f acq Arity => jump Fail
+is_function2 Fail=f Literal=q Arity | literal_is_export(Literal) =>
+is_function2 Fail=f c Arity => jump Fail
 is_function2 Fail=f Fun a => jump Fail
 
 is_function2 f? S s
diff --git a/erts/emulator/test/beam_literals_SUITE.erl b/erts/emulator/test/beam_literals_SUITE.erl
index 09761263e2..b447ca0210 100644
--- a/erts/emulator/test/beam_literals_SUITE.erl
+++ b/erts/emulator/test/beam_literals_SUITE.erl
@@ -248,35 +248,58 @@ literal_type_tests(Config) when is_list(Config) ->
     ok.
 
 make_test([{is_function=T,L}|Ts]) ->
-    [test(T, L),test(T, 0, L)|make_test(Ts)];
+    [guard_test(T, L),guard_test(T, 0, L),body_test(T, L),body_test(T, 0, L)|make_test(Ts)];
 make_test([{T,L}|Ts]) ->
-    [test(T, L)|make_test(Ts)];
+    [guard_test(T, L),body_test(T, L)|make_test(Ts)];
 make_test([]) -> [].
 
-test(T, L) ->
-    S = lists:flatten(io_lib:format("begin io:format(\"~~p~n\", [{~p,~p}]), if ~w(~w) -> true; true -> false end end. ", [T, L, T, L])),
-    {ok,Toks,_Line} = erl_scan:string(S),
-    {ok,E} = erl_parse:parse_exprs(Toks),
-    {value,Val,_Bs} = erl_eval:exprs(E, []),
+guard_test(_, L) when is_function(L) ->
+    %% Skip guard tests with exports - they are not literals
+    {atom,erl_anno:new(0),true};
+guard_test(T, L) ->
+    S = io_lib:format("begin io:format(\"~~p~n\", [{~p,~p}]), if ~w(~w) -> true; true -> false end end. ", [T, L, T, L]),
+    {Val,Expr} = eval_string(S),
+    Anno = erl_anno:new(0),
+    {match,Anno,{atom,Anno,Val},Expr}.
+
+guard_test(_, _, L) when is_function(L) ->
+    %% Skip guard tests with exports - they are not literals
+    {atom,erl_anno:new(0),true};
+guard_test(T, A, L) ->
+    S = io_lib:format("begin io:format(\"~~p~n\", [{~p,~p,~p}]), if ~w(~w, ~w) -> true; true -> false end end. ", [T,L,A,T,L,A]),
+    {Val,Expr} = eval_string(S),
+    Anno = erl_anno:new(0),
+    {match,Anno,{atom,Anno,Val},Expr}.
+
+body_test(T, L) ->
+    S = io_lib:format("begin io:format(\"~~p~n\", [{~p,~p}]), ~w(~w) end. ", [T,L,T,L]),
+    {Val,Expr} = eval_string(S),
     Anno = erl_anno:new(0),
-    {match,Anno,{atom,Anno,Val},hd(E)}.
+    {match,Anno,{atom,Anno,Val},Expr}.
 
-test(T, A, L) ->
-    S = lists:flatten(io_lib:format("begin io:format(\"~~p~n\", [{~p,~p,~p}]), if ~w(~w, ~w) -> true; true -> false end end. ",
-				    [T,L,A,T,L,A])),
-    {ok,Toks,_Line} = erl_scan:string(S),
+body_test(T, A, L) ->
+    S = io_lib:format("begin io:format(\"~~p~n\", [{~p,~p,~p}]), ~w(~w,~w) end. ", [T,L,A,T,L,A]),
+    {Val,Expr} = eval_string(S),
+    Anno = erl_anno:new(0),
+    {match,Anno,{atom,Anno,Val},Expr}.
+
+eval_string(S) ->
+    {ok,Toks,_Line} = erl_scan:string(lists:flatten(S)),
     {ok,E} = erl_parse:parse_exprs(Toks),
     {value,Val,_Bs} = erl_eval:exprs(E, []),
-    Anno = erl_anno:new(0),
-    {match,Anno,{atom,Anno,Val},hd(E)}.
-    
+    {Val,hd(E)}.
+
 literals() ->
     [42,
      3.14,
      -3,
      32982724987789283473473838474,
      [],
-     xxxx].
+     "abc",
+     <<"abc">>,
+     {},
+     xxxx,
+     fun erlang:erase/0].
 
 type_tests() ->
     [is_boolean,