Implement magic references

Magic references are *intentionally* indistinguishable from ordinary
references for the Erlang software. Magic references do not change
the language, and are intended as a pure runtime internal optimization.

An ordinary reference is typically used as a key in some table. A
magic reference has a direct pointer to a reference counted magic
binary. This makes it possible to implement various things without
having to do lookups in a table, but instead access the data directly.
Besides very fast lookups this can also improve scalability by
removing a potentially contended table. A couple of examples of
planned future usage of magic references are ETS table identifiers,
and BIF timer identifiers.

Besides future optimizations using magic references it should also
be possible to replace the exposed magic binary cludge with magic
references. That is, magic binaries that are exposed as empty
binaries to the Erlang software.

1 files changed, 44 insertions, 52 deletions

diff --git a/erts/emulator/beam/utils.c b/erts/emulator/beam/utils.c
index 25940edab7..fc459e17ad 100644
--- a/erts/emulator/beam/utils.c
+++ b/erts/emulator/beam/utils.c
@@ -1838,7 +1838,7 @@ make_internal_hash(Eterm term)
 	    break;
 	    case REF_SUBTAG:
 		UINT32_HASH(internal_ref_numbers(term)[0], HCONST_7);
-                ASSERT(internal_ref_no_of_numbers(term) == 3);
+                ASSERT(internal_ref_no_numbers(term) == 3);
                 UINT32_HASH_2(internal_ref_numbers(term)[1],
                               internal_ref_numbers(term)[2], HCONST_8);
                 goto pop_next;
@@ -1847,7 +1847,7 @@ make_internal_hash(Eterm term)
             {
                 ExternalThing* thing = external_thing_ptr(term);
 
-                ASSERT(external_thing_ref_no_of_numbers(thing) == 3);
+                ASSERT(external_thing_ref_no_numbers(thing) == 3);
                 /* See limitation #2 */
             #ifdef ARCH_64
                 POINTER_HASH(thing->node, HCONST_7);
@@ -2486,22 +2486,20 @@ tailrecur_ne:
 
 		anum = external_thing_ref_numbers(athing);
 		bnum = external_thing_ref_numbers(bthing);
-		alen = external_thing_ref_no_of_numbers(athing);
-		blen = external_thing_ref_no_of_numbers(bthing);
+		alen = external_thing_ref_no_numbers(athing);
+		blen = external_thing_ref_no_numbers(bthing);
 
 		goto ref_common;
+
 	    case REF_SUBTAG:
-		    if (!is_internal_ref(b))
-			goto not_equal;
 
-		    {
-			RefThing* athing = ref_thing_ptr(a);
-			RefThing* bthing = ref_thing_ptr(b);
-			alen = internal_thing_ref_no_of_numbers(athing);
-			blen = internal_thing_ref_no_of_numbers(bthing);
-			anum = internal_thing_ref_numbers(athing);
-			bnum = internal_thing_ref_numbers(bthing);
-		    }
+		if (!is_internal_ref(b))
+		    goto not_equal;
+
+		alen = internal_ref_no_numbers(a);
+		anum = internal_ref_numbers(a);
+		blen = internal_ref_no_numbers(b);
+		bnum = internal_ref_numbers(b);
 
 	    ref_common:
 		    ASSERT(alen > 0 && blen > 0);
@@ -3133,25 +3131,21 @@ tailrecur_ne:
 		 */
 
 		if (is_internal_ref(b)) {
-		    RefThing* bthing = ref_thing_ptr(b);
 		    bnode = erts_this_node;
-		    bnum = internal_thing_ref_numbers(bthing);
-		    blen = internal_thing_ref_no_of_numbers(bthing);
+		    blen = internal_ref_no_numbers(b);
+		    bnum = internal_ref_numbers(b);
 		} else if(is_external_ref(b)) {
 		    ExternalThing* bthing = external_thing_ptr(b);
 		    bnode = bthing->node;
 		    bnum = external_thing_ref_numbers(bthing);
-		    blen = external_thing_ref_no_of_numbers(bthing);
+		    blen = external_thing_ref_no_numbers(bthing);
 		} else {
 		    a_tag = REF_DEF;
 		    goto mixed_types;
 		}
-		{
-		    RefThing* athing = ref_thing_ptr(a);
-		    anode = erts_this_node;
-		    anum = internal_thing_ref_numbers(athing);
-		    alen = internal_thing_ref_no_of_numbers(athing);
-		}
+		anode = erts_this_node;
+		alen = internal_ref_no_numbers(a);
+		anum = internal_ref_numbers(a);
 
 	    ref_common:
 		CMP_NODES(anode, bnode);
@@ -3181,15 +3175,14 @@ tailrecur_ne:
 		goto pop_next;
 	    case (_TAG_HEADER_EXTERNAL_REF >> _TAG_PRIMARY_SIZE):
 		if (is_internal_ref(b)) {
-		    RefThing* bthing = ref_thing_ptr(b);
 		    bnode = erts_this_node;
-		    bnum = internal_thing_ref_numbers(bthing);
-		    blen = internal_thing_ref_no_of_numbers(bthing);
+		    blen = internal_ref_no_numbers(b);
+		    bnum = internal_ref_numbers(b);
 		} else if (is_external_ref(b)) {
 		    ExternalThing* bthing = external_thing_ptr(b);
 		    bnode = bthing->node;
 		    bnum = external_thing_ref_numbers(bthing);
-		    blen = external_thing_ref_no_of_numbers(bthing);
+		    blen = external_thing_ref_no_numbers(bthing);
 		} else {
 		    a_tag = EXTERNAL_REF_DEF;
 		    goto mixed_types;
@@ -3198,7 +3191,7 @@ tailrecur_ne:
 		    ExternalThing* athing = external_thing_ptr(a);
 		    anode = athing->node;
 		    anum = external_thing_ref_numbers(athing);
-		    alen = external_thing_ref_no_of_numbers(athing);
+		    alen = external_thing_ref_no_numbers(athing);
 		}
 		goto ref_common;
 	    default:
@@ -3575,40 +3568,39 @@ not_equal:
 Eterm
 store_external_or_ref_(Uint **hpp, ErlOffHeap* oh, Eterm ns)
 {
+    struct erl_off_heap_header *ohhp;
     Uint i;
     Uint size;
-    Uint *from_hp;
-    Uint *to_hp = *hpp;
+    Eterm *from_hp;
+    Eterm *to_hp = *hpp;
 
     ASSERT(is_external(ns) || is_internal_ref(ns));
 
-    if(is_external(ns)) {
-	from_hp = external_val(ns);
-	size = thing_arityval(*from_hp) + 1;
-	*hpp += size;
-
-	for(i = 0; i < size; i++)
-	    to_hp[i] = from_hp[i];
-
-	erts_smp_refc_inc(&((ExternalThing *) to_hp)->node->refc, 2);
-
-	((struct erl_off_heap_header*) to_hp)->next = oh->first;
-	oh->first = (struct erl_off_heap_header*) to_hp;
-
-	return make_external(to_hp);
-    }
-
-    /* Internal ref */
-    from_hp = internal_ref_val(ns);
-
+    from_hp = boxed_val(ns);
     size = thing_arityval(*from_hp) + 1;
-
     *hpp += size;
 
     for(i = 0; i < size; i++)
 	to_hp[i] = from_hp[i];
 
-    return make_internal_ref(to_hp);
+    if (is_external_header(*from_hp)) {
+	ExternalThing *etp = (ExternalThing *) from_hp;
+	ASSERT(is_external(ns));
+	erts_smp_refc_inc(&etp->node->refc, 2);
+    }
+    else if (is_ordinary_ref_thing(from_hp))
+	return make_internal_ref(to_hp);
+    else {
+	ErtsMRefThing *mreft = (ErtsMRefThing *) from_hp;
+	ASSERT(is_magic_ref_thing(from_hp));
+	erts_refc_inc(&mreft->mb->refc, 2);
+    }
+
+    ohhp = (struct erl_off_heap_header*) to_hp;
+    ohhp->next = oh->first;
+    oh->first = ohhp;
+
+    return make_boxed(to_hp);
 }
 
 Eterm