RFR: 8309136: [JVMCI] add -XX:+UseGraalJIT flag [v2]

[Doug Simon]

On Wed, 31 May 2023 23:21:16 GMT, Vladimir Kozlov <kvn at openjdk.org> wrote:

> > > Actually checking the availability of Graal can only be done in the code I linked to and it's only done on the first Graal JIT compilation (JVMCI compiler initialization is lazy to reduce impact to VM startup time).
> > 
> > 
> > Are you saying that the application will start executing quite happily in interpreted mode and then only abort when the JIT first kicks in? That would be a very bad thing to do unless you can guarantee the jit will kick in extremely early during VM init sequence.
> 
> I assume this is required only for Java Graal. For libgraal you can check library presence at the VM startup. Or I am wrong?

JVMCI compiler initialization is always lazy. It has been this way since the initial JVMCI implementation. Even libgraal initialization will impact VM startup. The first top tier compilation usually happens within the first 100 ms of VM execution.

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PR Comment: https://git.openjdk.org/jdk/pull/14231#issuecomment-1571093117