RFR: 8320276: Improve class initialization barrier in TemplateTable::_new [v3]

[David Holmes]

On Thu, 21 Dec 2023 17:51:04 GMT, Matias Saavedra Silva <matsaave at openjdk.org> wrote:

>> The class initialization barrier in TemplateTable::_new fast path check ensures that the class being instantiated is fully initialized. It can be improved by introducing additional fast path check when current thread is initializer thread as MacroAssembler::clinit_barrier() does. It avoids repeated calls into interpreter runtime for classes being initialized. This patch adds the optimization for x86 and aarch64. Verified with tier 1-5 tests.
>> 
>> This change was tested with Spring Petclinic which reported the following startup times:
>> 
>> Clean build:   #### Booted and returned in 161941ms
>> Patched build: #### Booted and returned in 160657ms
>
> Matias Saavedra Silva has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Fixed comments

Please update the comments on `supports_fast_class_init_checks` for all architectures so they are consistent. As it just a comment there are no concerns about build/test. Thanks.

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Changes requested by dholmes (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/17006#pullrequestreview-1793813583