RFR: 8256365: Clean up vtable initialization code [v3]

[David Holmes]

On Wed, 18 Nov 2020 03:55:19 GMT, Coleen Phillimore <coleenp at openjdk.org> wrote:

>> I was looking through this code because of JDK-8061949 and want to do some minor cleanups.
>> 1. There's a function in the wrong place (is_override)
>> 2. methodHandles that use mh()->is_native(), with extra (),
>> 3. some methods declared with TRAPS, that don't trap
>> 4. some multi-clause conditionals with confusing formatting
>> 5. extra InstanceKlass::cast() casts
>> 6. some useless asserts
>> 7. and potentially a bug with RedefineClasses where the method being added to the vtable may have been redefined in the constraint verification call. (noreg-hard)
>> 
>> Tested with tier1-3.
>
> Coleen Phillimore has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Rename is_override to can_be_overridden.

Marked as reviewed by dholmes (Reviewer).

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PR: https://git.openjdk.java.net/jdk/pull/1236