[9] RFR (M): 8050877: Improve code for pairwise argument conversions and value boxing/unboxing

[Vladimir Ivanov]

http://cr.openjdk.java.net/~vlivanov/8050877/webrev.00/
https://bugs.openjdk.java.net/browse/JDK-8050877

Improved MethodHandleImpl.makePairwiseConvert & ValueConversions.unbox 
and small cleanups in related code.

Also, improved method handle caching in ValueConversions.

MethodHandleImpl.makePairwiseConvert:
-     * @param level which strength of conversion is allowed
+     * @param strict if true, only asType conversions are allowed; if 
false, explicitCastArguments conversions allowed
+     * @param monobox if true, unboxing conversions are assumed to be 
exactly typed (Integer to int only, not long or double)

ValueConversions.unbox:
-    private static MethodHandle unbox(Wrapper wrap, boolean cast) {
+    private static MethodHandle unbox(Wrapper wrap, int kind) {
+        // kind 0 -> strongly typed with NPE
+        // kind 1 -> strongly typed but zero for null,
+        // kind 2 -> asType rules: accept multiple box types but only 
widening conversions with NPE
+        // kind 3 -> explicitCastArguments rules: allow narrowing 
conversions, zero for null
+        WrapperCache cache = UNBOX_CONVERSIONS[kind];

Testing: jdk/java/lang/invoke, jdk/java/util/streams, nashorn, octane w/ 
"-ea -esa" and COMPILE_THRESHOLD={0,30}.

Reviewed-by: vlivanov, ?
Contributed-by: john.r.rose at oracle.com

Thanks!

Best regards,
Vladimir Ivanov