RFR: 8257020: [JVMCI] enable a JVMCICompiler to specify which GCs it supports [v5]

[Doug Simon]

On Wed, 2 Dec 2020 17:41:49 GMT, Vladimir Kozlov <kvn at openjdk.org> wrote:

>>> Latest changes looks like reversal of original. Will GraalVM have additional checks to allow ask Graal before disabling JVMCI?
>> 
>> No, the changes in this PR are sufficient. When JVMCI support is added for Graal to be able to implement support for ZGC/Shenandoah/Epsilon, the `check_jvmci_supported_gc` implementation will be updated.
>
>> > Latest changes looks like reversal of original. Will GraalVM have additional checks to allow ask Graal before disabling JVMCI?
>> 
>> No, the changes in this PR are sufficient. When JVMCI support is added for Graal to be able to implement support for ZGC/Shenandoah/Epsilon, the `check_jvmci_supported_gc` implementation will be updated.
> 
> Okay. If you are fine with that.

There is the interesting question of whether explicit JVMCI API extensions are needed for Epsilon. @shipilev what's your intuition on that?

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PR: https://git.openjdk.java.net/jdk/pull/1423