From 28c4871c99229c0243d20bf7316bb3a77e30c614 Mon Sep 17 00:00:00 2001
From: Andy <anhans@microsoft.com>
Date: Thu, 8 Feb 2018 09:45:43 -0800
Subject: [PATCH] hasSameKeys: Simplify and optimize for identical maps
 (#21763)

---
 src/compiler/builder.ts | 10 ++--------
 1 file changed, 2 insertions(+), 8 deletions(-)

diff --git a/src/compiler/builder.ts b/src/compiler/builder.ts
index 886a2194bd9..121609db104 100644
--- a/src/compiler/builder.ts
+++ b/src/compiler/builder.ts
@@ -41,15 +41,9 @@ namespace ts {
         program: Program;
     }
 
-    function hasSameKeys<T, U>(map1: ReadonlyMap<T> | undefined, map2: ReadonlyMap<U> | undefined) {
-        if (map1 === undefined) {
-            return map2 === undefined;
-        }
-        if (map2 === undefined) {
-            return map1 === undefined;
-        }
+    function hasSameKeys<T, U>(map1: ReadonlyMap<T> | undefined, map2: ReadonlyMap<U> | undefined): boolean {
         // Has same size and every key is present in both maps
-        return map1.size === map2.size && !forEachKey(map1, key => !map2.has(key));
+        return map1 as ReadonlyMap<T | U> === map2 || map1 && map2 && map1.size === map2.size && !forEachKey(map1, key => !map2.has(key));
     }
 
     /**