RFR: 8329433: Reduce nmethod header size [v3]

[Vladimir Kozlov]

On Tue, 16 Apr 2024 02:34:29 GMT, Dean Long <dlong at openjdk.org> wrote:

>> Vladimir Kozlov has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Union fields which usages do not overlap
>
> src/hotspot/share/code/nmethod.hpp line 205:
> 
>> 203:       // offsets to find the receiver for non-static native wrapper frames.
>> 204:       ByteSize _native_receiver_sp_offset;
>> 205:       ByteSize _native_basic_lock_sp_offset;
> 
> Don't we need an assert in the accessor functions to make sure nmethod is native or not?

I thought about that but in both places where these accessors are called (`frame::get_native_monitor()` and `frame::get_native_receiver()`) there are such asserts already:
https://github.com/openjdk/jdk/blob/master/src/hotspot/share/runtime/frame.cpp#L1085

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PR Review Comment: https://git.openjdk.org/jdk/pull/18768#discussion_r1566650267