RFR: 8331087: Move immutable nmethod data from CodeCache

[Dean Long]

On Fri, 26 Apr 2024 21:16:03 GMT, Vladimir Kozlov <kvn at openjdk.org> wrote:

> Move immutable nmethod's data from CodeCache to C heap. It includes `dependencies, nul_chk_table, handler_table, scopes_pcs, scopes_data, speculations, jvmci_data`. It amounts for about 30% (optimized VM) of space in CodeCache.
> 
> Use HotSpot's `os::malloc()` to allocate memory in C heap for immutable nmethod's data. Bail out compilation if allocation failed.
> 
> Shuffle fields order and change some fields size from 4 to 2 bytes to avoid nmethod's header size increase.
> 
> Tested tier1-5, stress,xcomp
> 
> Our performance testing does not show difference.
> 
> Example of updated `-XX:+PrintNMethodStatistics` output is in JBS comment.

src/hotspot/share/code/nmethod.cpp line 1332:

> 1330: #if INCLUDE_JVMCI
> 1331:     _speculations_offset     = _scopes_data_offset;
> 1332:     _jvmci_data_offset       = _speculations_offset;

Why not use 0 for all these?

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PR Review Comment: https://git.openjdk.org/jdk/pull/18984#discussion_r1581642931