RFR: 8257020: [JVMCI] enable a JVMCICompiler to specify which GCs it supports [v4]

[Vladimir Kozlov]

On Fri, 27 Nov 2020 10:20:17 GMT, Doug Simon <dnsimon at openjdk.org> wrote:

>> A number of jtreg tests require a specific GC. These tests should be ignored when EnableJVMCI is true and the JVMCI compiler does not support the required GC.
>> 
>> This PR adds `JVMCICompiler.isGCSupported` and makes use of it in `WhiteBox.isGCSupported`.
>> 
>> Prior to this PR, a test requiring a GC not yet supported by a JVMCI compiler fail as follows:
>> Error occurred during initialization of VM
>> JVMCI Compiler does not support selected GC: epsilon gc
>
> Doug Simon has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains seven additional commits since the last revision:
> 
>  - Merge remote-tracking branch 'openjdk-jdk/master' into JDK-8257020
>  - implemented isGCSupported in Graal compiler
>  - removed JVMCI logic from GCConfig and introduced WhiteBox.isGCSupportedByJVMCI instead
>  - removed broken check_jvmci_supported_gc logic
>  - removed redundant signature
>  - move logic to GCConfig
>  - enable a JVMCICompiler to specify which GCs it supports

Looks good.

-------------

Marked as reviewed by kvn (Reviewer).

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