RFR: 8285364: Remove REF_ enum for java.lang.ref.Reference [v4]

[Kim Barrett]

On Fri, 29 Apr 2022 11:39:39 GMT, Albert Mingkun Yang <ayang at openjdk.org> wrote:

>> The `_reference_type` used to be initialized correctly in most cases, but
>> needed fixing up for a few cases during bootstrapping. With this change it is
>> *never* initialized correctly for Reference subtypes and always needs an
>> initialization kludge for them. That's not an improvement.
>
> `_reference_type` always gets the correct value after the constructor is run. The member initializer list just follows the convention of having all fields set. One could move this field inside the constructor body to ensure this field is set only once.

> The current approach limits the knowledge of non-strong ref types to `instanceRefKlass` file.

The mechanism used to compute the correct reftype is purely derived from the
parser, and to me looks like "parsing". So I think it would be better placed
with the parser. And that would also remove the need for the two-step
initialization of the InstanceKlass member.

With that in mind, I think the file scoped function determine_reference_type
in instanceRefKlass.cpp should instead be an ordinary public member function
`ClassFileParser::reference_type() const` (with appropriate adjustment of it's
implementation), called by the InstanceKlass constructor to initialize
`_reference_type`.

Associated with that are some other changes:
- The new InstanceRefKlass::set_reference_type is no longer needed.
- The new ClassFileParser::super_reference_type and
ClassFileParser::is_java_lang_ref_Reference_subclass don't need to be public.
(Assuming they exist at all after adjustment of ClassFileParser::reference_type.)

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PR: https://git.openjdk.org/jdk/pull/8332