Optimize KClass creation from Class instance

Don't create unnecessary iterator every time in HashPMap.get (see
https://github.com/hrldcpr/pcollections/pull/41). Also fix a warning and remove
misleading comment

core/reflection.jvm/src/kotlin/reflect/jvm/internal/kClassCache.kt

@@ -34,7 +34,7 @@ internal fun <T : Any> getOrCreateKotlinClass(jClass: Class<T>): KClassImpl<T> {
         @Suppress("UNCHECKED_CAST")
         val kClass = cached.get() as KClassImpl<T>?
         if (kClass?.jClass == jClass) {
-            return kClass!!
+            return kClass
         }
     }
     else if (cached != null) {
@@ -51,7 +51,6 @@ internal fun <T : Any> getOrCreateKotlinClass(jClass: Class<T>): KClassImpl<T> {
         // This is the most unlikely case: we found a cached array of references of length at least 2 (can't be 1 because
         // the single element would be cached instead), and none of those classes is the one we're looking for
         val size = cached.size
-        // Don't use Array constructor because it creates a lambda
         val newArray = arrayOfNulls<WeakReference<KClassImpl<*>>>(size + 1)
         // Don't use Arrays.copyOf because it works reflectively
         System.arraycopy(cached, 0, newArray, 0, size)

core/reflection.jvm/src/kotlin/reflect/jvm/internal/pcollections/ConsPStack.java

@@ -32,8 +32,8 @@ final class ConsPStack<E> implements Iterable<E> {
         return (ConsPStack<E>) EMPTY;
     }
 
-    private final E first;
-    private final ConsPStack<E> rest;
+    final E first;
+    final ConsPStack<E> rest;
     private final int size;
 
     private ConsPStack() { // EMPTY constructor

core/reflection.jvm/src/kotlin/reflect/jvm/internal/pcollections/HashPMap.java

@@ -28,7 +28,7 @@ public final class HashPMap<K, V> {
     @SuppressWarnings("unchecked")
     @NotNull
     public static <K, V> HashPMap<K, V> empty() {
-        return (HashPMap<K, V>) HashPMap.EMPTY;
+        return (HashPMap<K, V>) EMPTY;
     }
 
     private final IntTreePMap<ConsPStack<MapEntry<K, V>>> intMap;
@@ -49,9 +49,12 @@ public final class HashPMap<K, V> {
 
     public V get(Object key) {
         ConsPStack<MapEntry<K, V>> entries = getEntries(key.hashCode());
-        for (MapEntry<K, V> entry : entries)
+        while (entries != null && entries.size() > 0) {
+            MapEntry<K, V> entry = entries.first;
             if (entry.key.equals(key))
                 return entry.value;
+            entries = entries.rest;
+        }
         return null;
     }
 
@@ -86,9 +89,11 @@ public final class HashPMap<K, V> {
 
     private static <K, V> int keyIndexIn(ConsPStack<MapEntry<K, V>> entries, Object key) {
         int i = 0;
-        for (MapEntry<K, V> entry : entries) {
+        while (entries != null && entries.size() > 0) {
+            MapEntry<K, V> entry = entries.first;
             if (entry.key.equals(key))
                 return i;
+            entries = entries.rest;
             i++;
         }
         return -1;