Fix x/into perf problem when from is a small map

src/net/cgrand/xforms.cljc

@@ -7,9 +7,10 @@
       :clj (:require [net.cgrand.macrovich :as macros]))
   (:refer-clojure :exclude [some reduce reductions into count for partition
                             str last keys vals min max drop-last take-last
-                            sort sort-by time])
+                            sort sort-by time satisfies?])
   (:require [#?(:clj clojure.core :cljs cljs.core) :as core]
-    [net.cgrand.xforms.rfs :as rf])
+    [net.cgrand.xforms.rfs :as rf]
+            #?(:clj [clojure.core.protocols]))
   #?(:cljs (:import [goog.structs Queue])))
 
 (macros/deftime
@@ -124,8 +125,44 @@
 
 (macros/usetime
 
-(defn kvreducible? [coll]
- (satisfies? #?(:clj clojure.core.protocols/IKVReduce :cljs IKVReduce) coll))
+;; Workaround clojure.core/satisfies? being slow in Clojure
+;; see https://ask.clojure.org/index.php/3304/make-satisfies-as-fast-as-a-protocol-method-call
+#?(:cljs
+   (def satisfies? core/satisfies?)
+
+   :bb
+   (def satisfies? core/satisfies?)
+
+   :clj
+   (defn fast-satisfies?-fn
+     "Ported from https://github.com/clj-commons/manifold/blob/37658e91f836047a630586a909a2e22debfbbfc6/src/manifold/utils.clj#L77-L89"
+     [protocol-var]
+     (let [^java.util.concurrent.ConcurrentHashMap classes
+           (java.util.concurrent.ConcurrentHashMap.)]
+       (add-watch protocol-var ::memoization (fn [& _] (.clear classes)))
+       (fn [x]
+         (let [cls (class x)
+               val (.get classes cls)]
+           (if (nil? val)
+             (let [val (core/satisfies? @protocol-var x)]
+               (.put classes cls val)
+               val)
+             val))))))
+
+
+#?(:cljs
+   (defn kvreducible? [coll]
+     (satisfies? core/IKVReduce coll))
+
+   :clj
+   (let [satisfies-ikvreduce? #?(:bb #(satisfies? clojure.core.protocols/IKVReduce %)
+                                 :default (fast-satisfies?-fn #'clojure.core.protocols/IKVReduce))]
+     (if (satisfies-ikvreduce? (Object.))
+       (defn kvreducible?
+         "Clojure 1.11 makes everything satisfy IKVReduce, so we can short-circuit"
+         [_] true)
+       (defn kvreducible? [coll] (satisfies-ikvreduce? coll)))))
+
 
 (extend-protocol KvRfable
   #?(:clj Object :cljs default) (some-kvrf [_] nil)