Optimize the is_function/2 guard test

The is_function2 instruction is executed surprisingly
frequently when running dialyzer or the compiler. It
cannot hurt to optimize it a little.

5 files changed, 102 insertions, 18 deletions

diff --git a/erts/emulator/beam/beam_emu.c b/erts/emulator/beam/beam_emu.c
index 6b34024a5a..4ef06464f4 100644
--- a/erts/emulator/beam/beam_emu.c
+++ b/erts/emulator/beam/beam_emu.c
@@ -404,6 +404,7 @@ static BeamInstr* apply_fun(Process* p, Eterm fun,
 			    Eterm args, Eterm* reg) NOINLINE;
 static Eterm new_fun(Process* p, Eterm* reg,
 		     ErlFunEntry* fe, int num_free) NOINLINE;
+static int is_function2(Eterm Term, Uint arity);
 static Eterm erts_gc_new_map(Process* p, Eterm* reg, Uint live,
                              Uint n, BeamInstr* ptr) NOINLINE;
 static Eterm erts_gc_new_small_map_lit(Process* p, Eterm* reg, Eterm keys_literal,
@@ -2662,6 +2663,19 @@ new_fun(Process* p, Eterm* reg, ErlFunEntry* fe, int num_free)
     return make_fun(funp);
 }
 
+static int
+is_function2(Eterm Term, Uint arity)
+{
+    if (is_fun(Term)) {
+	ErlFunThing* funp = (ErlFunThing *) fun_val(Term);
+	return funp->arity == arity;
+    } else if (is_export(Term)) {
+	Export* exp = (Export *) (export_val(Term)[1]);
+	return exp->info.mfa.arity == arity;
+    }
+    return 0;
+}
+
 static Eterm get_map_element(Eterm map, Eterm key)
 {
     Uint32 hx;
diff --git a/erts/emulator/beam/beam_load.c b/erts/emulator/beam/beam_load.c
index 400a58a75c..7ff55e8927 100644
--- a/erts/emulator/beam/beam_load.c
+++ b/erts/emulator/beam/beam_load.c
@@ -4298,6 +4298,72 @@ gen_make_fun2(LoaderState* stp, GenOpArg idx)
 }
 
 static GenOp*
+gen_is_function2(LoaderState* stp, GenOpArg Fail, GenOpArg Fun, GenOpArg Arity)
+{
+    GenOp* op;
+    int literal_arity =  Arity.type == TAG_i;
+    int fun_is_reg = Fun.type == TAG_x || Fun.type == TAG_y;
+
+    NEW_GENOP(stp, op);
+    op->next = NULL;
+
+    if (fun_is_reg &&literal_arity) {
+        /*
+         * Most common case. Fun in a register and arity
+         * is an integer literal.
+         */
+        if (Arity.val > MAX_ARG) {
+            /* Arity is negative or too big. */
+            op->op = genop_jump_1;
+            op->arity = 1;
+            op->a[0] = Fail;
+            return op;
+        } else {
+            op->op = genop_hot_is_function2_3;
+            op->arity = 3;
+            op->a[0] = Fail;
+            op->a[1] = Fun;
+            op->a[2].type = TAG_u;
+            op->a[2].val = Arity.val;
+            return op;
+        }
+    } else {
+        /*
+         * Handle extremely uncommon cases by a slower sequence.
+         */
+        GenOp* move_fun;
+        GenOp* move_arity;
+
+        NEW_GENOP(stp, move_fun);
+        NEW_GENOP(stp, move_arity);
+
+        move_fun->next = move_arity;
+        move_arity->next = op;
+
+        move_fun->arity = 2;
+        move_fun->op = genop_move_2;
+        move_fun->a[0] = Fun;
+        move_fun->a[1].type = TAG_x;
+        move_fun->a[1].val = 1022;
+
+        move_arity->arity = 2;
+        move_arity->op = genop_move_2;
+        move_arity->a[0] = Arity;
+        move_arity->a[1].type = TAG_x;
+        move_arity->a[1].val = 1023;
+
+        op->op = genop_cold_is_function2_3;
+        op->arity = 3;
+        op->a[0] = Fail;
+        op->a[1].type = TAG_x;
+        op->a[1].val = 1022;
+        op->a[2].type = TAG_x;
+        op->a[2].val = 1023;
+        return move_fun;
+    }
+}
+
+static GenOp*
 tuple_append_put5(LoaderState* stp, GenOpArg Arity, GenOpArg Dst,
 		  GenOpArg* Puts, GenOpArg S1, GenOpArg S2, GenOpArg S3,
 		  GenOpArg S4, GenOpArg S5)
@@ -4463,19 +4529,6 @@ 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/instrs.tab b/erts/emulator/beam/instrs.tab
index df60e889f3..e55c4a112d 100644
--- a/erts/emulator/beam/instrs.tab
+++ b/erts/emulator/beam/instrs.tab
@@ -709,12 +709,18 @@ is_function(Fail, Src) {
     }
 }
 
-is_function2(Fail, Fun, Arity) {
+cold_is_function2(Fail, Fun, Arity) {
     if (erl_is_function(c_p, $Fun, $Arity) != am_true ) {
         $FAIL($Fail);
     }
 }
 
+hot_is_function2(Fail, Fun, Arity) {
+    if (!is_function2($Fun, $Arity)) {
+        $FAIL($Fail);
+    }
+}
+
 is_integer(Fail, Src) {
     if (is_not_integer($Src)) {
         $FAIL($Fail);
diff --git a/erts/emulator/beam/ops.tab b/erts/emulator/beam/ops.tab
index ee99c9e563..8e730e42d6 100644
--- a/erts/emulator/beam/ops.tab
+++ b/erts/emulator/beam/ops.tab
@@ -719,11 +719,12 @@ is_boolean Fail=f ac => jump Fail
 is_boolean f? xy
 %hot
 
-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 Fail=f Fun Arity => gen_is_function2(Fail, Fun, Arity)
 
-is_function2 f? S s
+%cold
+cold_is_function2 f? x x
+%hot
+hot_is_function2 f? S t
 
 # Allocating & initializing.
 allocate Need Regs | init Y => allocate_init Need Regs Y
diff --git a/erts/emulator/test/fun_SUITE.erl b/erts/emulator/test/fun_SUITE.erl
index f8a879182e..4042b58ff2 100644
--- a/erts/emulator/test/fun_SUITE.erl
+++ b/erts/emulator/test/fun_SUITE.erl
@@ -710,6 +710,16 @@ t_is_function2(Config) when is_list(Config) ->
     bad_arity({}),
     bad_arity({a,b}),
     bad_arity(self()),
+
+    %% Bad arity argument in guard test.
+    Fun = fun erlang:abs/1,
+    ok = if
+             is_function(Fun, -1) -> error;
+             is_function(Fun, 256) -> error;
+             is_function(Fun, a) -> error;
+             is_function(Fun, Fun) -> error;
+             true -> ok
+         end,
     ok.
 
 bad_arity(A) ->