Perf regression accessing fields in JDK21

[Aleksey Shipilev]

Hi Radim,

On 14.03.25 11:21, Radim Vansa wrote:
> I am attaching a reproducer; this creates a class with 21,000 fields,
> compiles it and executes this (all that the class does is to initialize
> all its fields). On JDK 17 running this reports 581 ms; on JDK 21 the
> test takes 8017 ms on my laptop.

Right. Please submit the RFE with your reproducer.

> I was able to avoid the second iteration by passing FieldInfo to
> reinitialize() and the execution went down to 5712 ms, but I don't see a
> simple solution that would make the first iteration more efficient. 

I recall looking at this when optimizing heap dumps, and I think we would not be able to avoid O(n) 
on initial field resolution. But I would expect incremental improvements to this code are possible.

Thanks,
-Aleksey