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

[Yudi Zheng]

On Thu, 19 Sep 2024 14:22:51 GMT, Stefan Karlsson <stefank at openjdk.org> wrote:

>> We haven't decided whether or not we will git rid of ```Klass::_prototype_header``` before intergrating this PR, or not. @stefank could point you to a WIP branch, if that's helpful.
>
> 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)                                    \

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PR Review Comment: https://git.openjdk.org/jdk/pull/20677#discussion_r1778884055