RFR: 8331341: secondary_super_cache does not scale well: C1 and interpreter [v6]

[Andrew Haley]

On Wed, 24 Jul 2024 19:09:06 GMT, Vladimir Ivanov <vlivanov at openjdk.org> wrote:

>>> > Also also, Klass::is_subtype_of() is used for C1 runtime.
>>> 
>>> Can you elaborate, please?
>> 
>> Sorry, that was rather vague. In C1-compiled code, the Java method `Class::isInstance(Object)`calls `Klass::is_subtype_of()`. 
>> 
>> In general, I find it difficult to decide how much work, if any, should be done to improve C1 performance. Clearly, if C1 exists only to help with startup time in a tiered compilation system, the answer is "not much".
>
> Thanks, now I see that `Class::isInstance(Object)` is backed by `Runtime1::is_instance_of()` which uses `oopDesc::is_a()` to do the job.
> 
> If it turns out to be performance critical, the intrinsic implementation should be rewritten to exercise existing subtype checking support in C1. As it is implemented now, it's already quite inefficient.

I did write an intrinsic for that, but it made this patch even larger. I have a small patch for C1, for some other time.

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PR Review Comment: https://git.openjdk.org/jdk/pull/19989#discussion_r1691491950