File 4321-Slightly-optimize-lists-enumerate-1-2.patch of Package erlang

From ddbb190b3fd4051651d5021e54997a50c4c953fc Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn=20Gustavsson?= <bjorn@erlang.org>
Date: Mon, 21 Feb 2022 14:31:08 +0100
Subject: [PATCH] Slightly optimize lists:enumerate/1,2

Only test that `Index` is an integer once, and not once for each
list element.
---
 lib/stdlib/src/lists.erl | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/lib/stdlib/src/lists.erl b/lib/stdlib/src/lists.erl
index b2d2c33ea3..c429e15263 100644
--- a/lib/stdlib/src/lists.erl
+++ b/lib/stdlib/src/lists.erl
@@ -962,17 +962,20 @@ keymap(Fun, Index, []) when is_integer(Index), Index >= 1,
       List2 :: [{Index, T}],
       Index :: integer(),
       T :: term().
-enumerate(List1) ->
-    enumerate(1, List1).
+enumerate(List1) when is_list(List1) ->
+    enumerate_1(1, List1).
 
 -spec enumerate(Index, List1) -> List2 when
       List1 :: [T],
       List2 :: [{Index, T}],
       Index :: integer(),
       T :: term().
-enumerate(Index, [H|T]) when is_integer(Index) ->
-    [{Index, H}|enumerate(Index + 1, T)];
-enumerate(Index, []) when is_integer(Index) ->
+enumerate(Index, List1) when is_integer(Index), is_list(List1) ->
+    enumerate_1(Index, List1).
+
+enumerate_1(Index, [H|T]) ->
+    [{Index, H}|enumerate_1(Index + 1, T)];
+enumerate_1(_Index, []) ->
     [].
 
 %%% Suggestion from OTP-2948: sort and merge with Fun.
-- 
2.34.1