From 5a57139d91c8bf02c420e8528f8544b9c2c30a87 Mon Sep 17 00:00:00 2001
From: Dag Wieers <dag@wieers.com>
Date: Thu, 18 Feb 2016 15:59:57 +0100
Subject: [PATCH] Improve efficiency of merge_hash

This is related to #14559, but only the part for Ansible v2.0

This commit makes merging empty dicts, or equal dicts more efficient.

I noticed that while debugging merge_hash a lot of merges related to empty dictionaries and sometimes also identical dictionaries.
---
 lib/ansible/utils/vars.py | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/lib/ansible/utils/vars.py b/lib/ansible/utils/vars.py
index 4d44a068c20..73ba52b4b39 100644
--- a/lib/ansible/utils/vars.py
+++ b/lib/ansible/utils/vars.py
@@ -74,6 +74,12 @@ def merge_hash(a, b):
     """
 
     _validate_mutable_mappings(a, b)
+
+    # if a is empty or equal to b, return b
+    if a == {} or a == b:
+        return b.copy()
+
+    # if b is empty the below unfolds quickly
     result = a.copy()
 
     # next, iterate over b keys and values