RFR: 8349088: De-virtualize Codeblob and nmethod [v2]

[Chris Plummer]

On Mon, 10 Feb 2025 02:47:58 GMT, Chris Plummer <cjplummer at openjdk.org> wrote:

>> Vladimir Kozlov has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Fix Zero and Minimal VM builds
>
> src/jdk.hotspot.agent/share/classes/sun/jvm/hotspot/code/CodeCache.java line 38:
> 
>> 36: public class CodeCache {
>> 37:   private static GrowableArray<CodeHeap> heapArray;
>> 38:   private static VirtualConstructor virtualConstructor;
> 
> What is the reason for switching from the virtualConstructor/hashMap approach to using getClassFor()? The hashmap is the model for JavaThread, MetaData, and CollectedHeap subtypes.

I think I found the answer. Since there is no longer a vtable, TypeDataBase.addressTypeIsEqualToType() will no longer work for Codeblobs. I was wondering if the lack of a vtable might have some negative impact. Glad to see you found a solution. I hope the lack of a vtable does not creep in elsewhere. I know it will have some negative impact on things like the "findpc" functionality, which will no longer be able to tell the user that an address points to a Codeblob instance. There's no test for this, but users might run across it.

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PR Review Comment: https://git.openjdk.org/jdk/pull/23533#discussion_r1948352958