RFR: 8331341: secondary_super_cache does not scale well: C1 and interpreter [v5]

[Vladimir Ivanov]

On Mon, 22 Jul 2024 16:36:25 GMT, Andrew Haley <aph at openjdk.org> wrote:

>>> Alternatively, `Klass::is_subtype_of()` can unconditionally perform linear search over secondary_supers array.
>>> 
>>> Even though I very much like to see table lookup written in C++ (accompanying heavily optimized platform-specific MacroAssembler variants), it would make C++ runtime even simpler.
>> 
>> It would, but there is something to be said for being able to provide a fast "no" answer for interface membership. I'll agree it's probably not a huge difference. I guess `is_cloneable_fast()` exists only because searching the interfaces is slow.
>> Also, if table lookup is written in C++ but not used, it will rot.
>> Also also, `Klass::is_subtype_of()` is used for C1 runtime.
>
> Thinking about it some more, I don't really mind. There may be some virtue to moving lookup_secondary_supers_table() to a comment in the back end(s), and the expansion of population_count() is rather bloaty.

> Also also, Klass::is_subtype_of() is used for C1 runtime.

Can you elaborate, please? What I'm seeing in `Runtime1::generate_code_for()` for `slow_subtype_check` is a call into `MacroAssembler::check_klass_subtype_slow_path()`.

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PR Review Comment: https://git.openjdk.org/jdk/pull/19989#discussion_r1688586602