8300237: Minor improvements in MethodHandles

Reviewed-by: redestad

Author: Sergey Tsypanov

src/java.base/share/classes/java/lang/invoke/MethodHandles.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2008, 2022, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2008, 2023, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -59,6 +59,7 @@
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.BitSet;
+import java.util.Comparator;
 import java.util.Iterator;
 import java.util.List;
 import java.util.Objects;
@@ -6744,25 +6745,19 @@ private static void loopChecks1a(int i, MethodHandle in, MethodHandle st) {
     }
 
     private static List<Class<?>> longestParameterList(Stream<MethodHandle> mhs, int skipSize) {
-        final List<Class<?>> empty = List.of();
-        final List<Class<?>> longest = mhs.filter(Objects::nonNull).
+        return mhs.filter(Objects::nonNull)
                 // take only those that can contribute to a common suffix because they are longer than the prefix
-                        map(MethodHandle::type).
-                        filter(t -> t.parameterCount() > skipSize).
-                        map(MethodType::parameterList).
-                        reduce((p, q) -> p.size() >= q.size() ? p : q).orElse(empty);
-        return longest.isEmpty() ? empty : longest.subList(skipSize, longest.size());
-    }
-
-    private static List<Class<?>> longestParameterList(List<List<Class<?>>> lists) {
-        final List<Class<?>> empty = List.of();
-        return lists.stream().reduce((p, q) -> p.size() >= q.size() ? p : q).orElse(empty);
+                .map(MethodHandle::type)
+                .filter(t -> t.parameterCount() > skipSize)
+                .max(Comparator.comparingInt(MethodType::parameterCount))
+                .map(methodType -> List.of(Arrays.copyOfRange(methodType.ptypes(), skipSize, methodType.parameterCount())))
+                .orElse(List.of());
     }
 
     private static List<Class<?>> buildCommonSuffix(List<MethodHandle> init, List<MethodHandle> step, List<MethodHandle> pred, List<MethodHandle> fini, int cpSize) {
         final List<Class<?>> longest1 = longestParameterList(Stream.of(step, pred, fini).flatMap(List::stream), cpSize);
         final List<Class<?>> longest2 = longestParameterList(init.stream(), 0);
-        return longestParameterList(List.of(longest1, longest2));
+        return longest1.size() >= longest2.size() ? longest1 : longest2;
     }
 
     private static void loopChecks1b(List<MethodHandle> init, List<Class<?>> commonSuffix) {