same treatment for HashMap and Set

Author: swannodette

src/main/cljs/cljs/core.cljs

@@ -12816,10 +12816,12 @@ reduces them without incurring seq initialization"
               i (scan-array-equiv 2 k new-bucket)]
           (aset new-hashobj h new-bucket)
           (if (some? i)
-            (do
-              ; found key, replace
-              (aset new-bucket (inc i) v)
-              (HashMap. meta count new-hashobj nil))
+            (if (identical? v (aget new-bucket (inc i)))
+              coll
+              (do
+                ; found key, replace
+                (aset new-bucket (inc i) v)
+                (HashMap. meta count new-hashobj nil)))
             (do
               ; did not find key, append
               (.push new-bucket k v)
@@ -12958,7 +12960,10 @@ reduces them without incurring seq initialization"
 
   ICollection
   (-conj [coll o]
-    (Set. meta (assoc hash-map o o) nil))
+    (let [new-hash-map (assoc hash-map o o)]
+      (if (identical? new-hash-map hash-map)
+        coll
+        (Set. meta new-hash-map nil))))
 
   IEmptyableCollection
   (-empty [coll] (with-meta (. Set -EMPTY) meta))