RFR: 8377597: [Leyden] Improve peak performance when AOT code is used

[Vladimir Kozlov]

On Wed, 11 Feb 2026 21:18:40 GMT, Dan Heidinga <heidinga at openjdk.org> wrote:

>> Currently some AOT code could be used for long time after startup. It could case peak performance regression because AOT code is conservative and have several restrictions on optimizations it can do.
>> 
>> Introduce AOT code entry counter to request JIT compilation and replace AOT code after some threshold is reached. Use invocation count of C2 code during training run as threshold for AOT code replacement during production run.
>> 
>> The counts collected during training run are scaled based on hyperbolic saturation curve formula:
>> 
>> 
>>    int scaled_limit = (AOTCodeInvokeBase + limit / (1.0 + limit / (100000.0 * AOTCodeInvokeScale)));
>> 
>> where `AOTCodeInvokeBase` (default 100.) and `AOTCodeInvokeScale` (default 1.) are diagnostic flags.
>> This scaling limits threshold to 100K for higher counts.
>> 
>> Here some results running JavacBanch JMH benchmark on linux-x64 (numactl -C 0-3 -m 0`)
>> 
>> 
>> java -jar javac.jar -f 1 -bm ss -wi 0 -i 100 JavacBench.helloWorld1k
>> 
>> 
>> <img width="781" height="466" alt="Screenshot 2026-02-10 at 1 25 30 PM" src="https://github.com/user-attachments/assets/58d973bf-9881-45d9-acb8-40b18ca02a06" />
>> 
>> 
>> <img width="486" height="178" alt="Screenshot 2026-02-10 at 1 22 24 PM" src="https://github.com/user-attachments/assets/19fff702-2302-4e43-a093-5c6981a069ba" />
>> 
>> ...
>> <img width="479" height="153" alt="Screenshot 2026-02-10 at 1 24 09 PM" src="https://github.com/user-attachments/assets/72e9d81d-bce2-482c-aaea-a32a192a8899" />
>
> src/hotspot/share/ci/ciObjectFactory.cpp line 426:
> 
>> 424:   } else if (o->is_methodCounters()) {
>> 425:     // Hold methodHandle alive - might not be necessary ???
>> 426:     methodHandle h_m(THREAD, ((MethodCounters*)o)->method());
> 
> Either `o` is kept alive already by something else, or the `methodHandle` here is insufficient.
> 
> If `o` is not already kept alive by something, it could be GC'd before the `methodHandle` is created and we'd be operating on invalid data.

I think MethodData and MethodCounters are only cleared when their holder Method is cleared.
Also I don't need MH here (and dubious comment) because we already created MH in caller 
`ciMethod::ensure_method_counters()`

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PR Review Comment: https://git.openjdk.org/leyden/pull/110#discussion_r2796207930