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.

1 files changed, 4 insertions, 1 deletions

diff --git a/lib/compiler/src/sys_core_fold.erl b/lib/compiler/src/sys_core_fold.erl
index a9bd363ee1..e39b9df218 100644
--- a/lib/compiler/src/sys_core_fold.erl
+++ b/lib/compiler/src/sys_core_fold.erl
@@ -392,7 +392,7 @@ expr(#c_receive{clauses=Cs0,timeout=T0,action=A0}=Recv, Ctxt, Sub) ->
 expr(#c_apply{anno=Anno,op=Op0,args=As0}=App, _, Sub) ->
     Op1 = expr(Op0, value, Sub),
     As1 = expr_list(As0, value, Sub),
-    case cerl:is_data(Op1) of
+    case cerl:is_data(Op1) andalso not is_literal_fun(Op1) of
         false ->
 	    App#c_apply{op=Op1,args=As1};
 	true ->
@@ -487,6 +487,9 @@ bitstr_list(Es, Sub) ->
 bitstr(#c_bitstr{val=Val,size=Size}=BinSeg, Sub) ->
     BinSeg#c_bitstr{val=expr(Val, Sub),size=expr(Size, value, Sub)}.
 
+is_literal_fun(#c_literal{val=F}) -> is_function(F);
+is_literal_fun(_) -> false.
+
 %% is_safe_simple(Expr, Sub) -> true | false.
 %%  A safe simple cannot fail with badarg and is safe to use
 %%  in a guard.