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

[Stefan Karlsson]

On Tue, 24 Nov 2020 23:46:17 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

Could this be done without adding JVMCI code to GCConfig::is_gc_supported? Could you extend VMProps.java:
    protected void vmGC(SafeMap map) {
        var isGraalEnabled = Compiler.isGraalEnabled();
        for (GC gc: GC.values()) {
            map.put("vm.gc." + gc.name(),
                    () -> "" + (gc.isSupported()
                            && (!isGraalEnabled || isGcSupportedByGraal(gc))
                            && (gc.isSelected() || GC.isSelectedErgonomically())));
        }
    }
and add:
`!isJvcmiEnabled || isGcSupportedByJvmci(gc)`
plus necessary JVMCI code to implement that?

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

Changes requested by stefank (Reviewer).

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