From c09b5941ce31be3cb08818533917afdeaf799575 Mon Sep 17 00:00:00 2001
From: sundb <sundbcn@gmail.com>
Date: Mon, 9 Nov 2020 20:16:09 +0800
Subject: [PATCH] optimization src/adlist.c:listJoin()

---
 src/adlist.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/src/adlist.c b/src/adlist.c
index bc06ffc8f..7670b2c10 100644
--- a/src/adlist.c
+++ b/src/adlist.c
@@ -360,15 +360,16 @@ void listRotateHeadToTail(list *list) {
 /* Add all the elements of the list 'o' at the end of the
  * list 'l'. The list 'other' remains empty but otherwise valid. */
 void listJoin(list *l, list *o) {
-    if (o->head)
-        o->head->prev = l->tail;
+    if (o->len == 0) return;
+
+    o->head->prev = l->tail;
 
     if (l->tail)
         l->tail->next = o->head;
     else
         l->head = o->head;
 
-    if (o->tail) l->tail = o->tail;
+    l->tail = o->tail;
     l->len += o->len;
 
     /* Setup other as an empty list. */