From 0916c5c6e536affca1f6f0c7693d68fb64843c1c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Micha=C5=82=20Muska=C5=82a?= <michal@muskala.eu>
Date: Tue, 17 Jul 2018 18:38:10 +0200
Subject: maps:new/0 is no longer a BIF

Implementing it in Erlang allows taking advantage of the literal pool
optimisation, this means the function implemented in Erlang does no
allocations, while the BIF had to allocate new map each time it was
called. Benchmarks show the function is also slightly faster now.
---
 erts/emulator/beam/bif.tab   |  1 -
 erts/emulator/beam/erl_map.c | 19 -------------------
 lib/stdlib/src/maps.erl      | 16 +++++++---------
 3 files changed, 7 insertions(+), 29 deletions(-)

diff --git a/erts/emulator/beam/bif.tab b/erts/emulator/beam/bif.tab
index 7548924178..a770524221 100644
--- a/erts/emulator/beam/bif.tab
+++ b/erts/emulator/beam/bif.tab
@@ -629,7 +629,6 @@ bif maps:from_list/1
 bif maps:is_key/2
 bif maps:keys/1
 bif maps:merge/2
-bif maps:new/0
 bif maps:put/3
 bif maps:remove/2
 bif maps:update/3
diff --git a/erts/emulator/beam/erl_map.c b/erts/emulator/beam/erl_map.c
index cba17d3e6a..4a1fe4470e 100644
--- a/erts/emulator/beam/erl_map.c
+++ b/erts/emulator/beam/erl_map.c
@@ -1505,25 +1505,6 @@ int hashmap_key_hash_cmp(Eterm* ap, Eterm* bp)
     return ap ? -1 : 1;
 }
 
-/* maps:new/0 */
-
-BIF_RETTYPE maps_new_0(BIF_ALIST_0) {
-    Eterm* hp;
-    Eterm tup;
-    flatmap_t *mp;
-
-    hp    = HAlloc(BIF_P, (MAP_HEADER_FLATMAP_SZ + 1));
-    tup   = make_tuple(hp);
-    *hp++ = make_arityval(0);
-
-    mp    = (flatmap_t*)hp;
-    mp->thing_word = MAP_HEADER_FLATMAP;
-    mp->size = 0;
-    mp->keys = tup;
-
-    BIF_RET(make_flatmap(mp));
-}
-
 /* maps:put/3 */
 
 BIF_RETTYPE maps_put_3(BIF_ALIST_3) {
diff --git a/lib/stdlib/src/maps.erl b/lib/stdlib/src/maps.erl
index 60463feec2..6f5553c769 100644
--- a/lib/stdlib/src/maps.erl
+++ b/lib/stdlib/src/maps.erl
@@ -21,7 +21,7 @@
 -module(maps).
 
 -export([get/3, filter/2,fold/3,
-         map/2, size/1,
+         map/2, size/1, new/0,
          update_with/3, update_with/4,
          without/2, with/2,
          iterator/1, next/1]).
@@ -29,7 +29,7 @@
 %% BIFs
 -export([get/2, find/2, from_list/1,
          is_key/2, keys/1, merge/2,
-         new/0, put/3, remove/2, take/2,
+         put/3, remove/2, take/2,
          to_list/1, update/3, values/1]).
 
 -opaque iterator() :: {term(), term(), iterator()}
@@ -91,13 +91,6 @@ keys(_) -> erlang:nif_error(undef).
 merge(_,_) -> erlang:nif_error(undef).
 
 
-
--spec new() -> Map when
-    Map :: map().
-
-new() -> erlang:nif_error(undef).
-
-
 %% Shadowed by erl_bif_types: maps:put/3
 -spec put(Key,Value,Map1) -> Map2 when
     Key :: term(),
@@ -157,6 +150,11 @@ values(_) -> erlang:nif_error(undef).
 
 %% End of BIFs
 
+-spec new() -> Map when
+    Map :: #{}.
+
+new() -> #{}.
+
 -spec update_with(Key,Fun,Map1) -> Map2 when
       Key :: term(),
       Map1 :: map(),
-- 
cgit v1.2.3


From 29eced05732b65f7663766014f1457dfc456eae8 Mon Sep 17 00:00:00 2001
From: Sverker Eriksson <sverker@erlang.org>
Date: Tue, 17 Jul 2018 20:24:58 +0200
Subject: Rebuild bootstrap for maps.erl

---
 bootstrap/lib/stdlib/ebin/maps.beam | Bin 3520 -> 3552 bytes
 1 file changed, 0 insertions(+), 0 deletions(-)

diff --git a/bootstrap/lib/stdlib/ebin/maps.beam b/bootstrap/lib/stdlib/ebin/maps.beam
index ec0ebce58a..e24b5955d5 100644
Binary files a/bootstrap/lib/stdlib/ebin/maps.beam and b/bootstrap/lib/stdlib/ebin/maps.beam differ
-- 
cgit v1.2.3