[lworld] RFR: Add Class.isIdentity

[Mandy Chung]

On Wed, 1 Jun 2022 16:57:59 GMT, Roger Riggs <rriggs at openjdk.org> wrote:

>> src/hotspot/share/oops/instanceKlass.cpp line 3398:
>> 
>>> 3396:     }
>>> 3397:   }
>>> 3398:   // Do not strip ACC_SUPER, its ACC_IDENTITY now
>> 
>> I think this should apply only if `EnableValhalla` (or `--enable-preview` is set).
>
> The semantics of the bit are dependent on (at least) the class file version.
> That's part of the modifier problem, the bit(s) are/will/need to be interpreted differently depending on the class file version and source  (class vs member).  Solution is TBD.
> Preview is not implemented yet.

I expect when `--enable-preview` is implemented, `EnableValhalla` or some other flag can be used to detect that.   The class file version (`ClassFileParser::supports_inline_types`) only applies to a single class.   When running with value types enabled, `Class::isIdentity` should return true for classes of a class file version that does not support value type.   That's why I think `if (EnableValhalla)` should be adequate for this patch until preview is implemented.

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PR: https://git.openjdk.java.net/valhalla/pull/700