RFR: 8305895: Implement JEP 450: Compact Object Headers (Experimental) [v9]

[Stefan Karlsson]

On Fri, 27 Sep 2024 16:31:55 GMT, Yudi Zheng <yzheng at openjdk.org> wrote:

>> This is my current work-in-progress code:
>> https://github.com/stefank/jdk/compare/pull/20677...stefank:jdk:lilliput_remove_prototype_header_wip_2
>> 
>> I've made some large rewrites and I'm currently running it through functional testing.
>
> If @stefank 's patch does not go in this PR, could you please export `Klass::_prototype_header` to JVMCI? Thanks!
> 
> diff --git a/src/hotspot/share/jvmci/vmStructs_jvmci.cpp b/src/hotspot/share/jvmci/vmStructs_jvmci.cpp
> index 9d1b8a1cb9f..e462025074f 100644
> --- a/src/hotspot/share/jvmci/vmStructs_jvmci.cpp
> +++ b/src/hotspot/share/jvmci/vmStructs_jvmci.cpp
> @@ -278,6 +278,7 @@
>    nonstatic_field(Klass,                       _bitmap,                                       uintx)                                 \
>    nonstatic_field(Klass,                       _hash_slot,                                    uint8_t)                               \
>    nonstatic_field(Klass,                       _misc_flags._flags,                            u1)                                    \
> +  nonstatic_field(Klass,                       _prototype_header,                             markWord)                              \
>                                                                                                                                       \
>    nonstatic_field(LocalVariableTableElement,   start_bci,                                     u2)                                    \
>    nonstatic_field(LocalVariableTableElement,   length,                                        u2)                                    \

My patch will not be included in this PR. After JEP 450 has been delivered we'll reconsider if we want that patch or not.

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PR Review Comment: https://git.openjdk.org/jdk/pull/20677#discussion_r1778950736