RFR: 8277878: Fix compiler tests after JDK-8275908

[Volker Simonis]

On Mon, 29 Nov 2021 10:33:29 GMT, Christian Hagedorn <chagedorn at openjdk.org> wrote:

>> This is a quick fix for the two compiler tests introduced by JDK-8275908. The test explicitly added SerialGC in the parameter list which leads to a garbage collector conflict, if the tests are run with some other Garbage collector.
>> 
>> It was suggested to fix this by adding a `@requires vm.gc.Serial` tag but this is not necessary because the tests are actually GC-agnostic so I've removed the `-XX:+UseSerialGC` parameter from the test command line instead.
>> 
>> After the fix it was necessary to refine the check for whether the test JVM has JVMCI support built-in. Before the fix, I used  `WhiteBox.getWhiteBox().isJVMCISupportedByGC()` which worked fine if only running with SerialGC. Now that we can run with GCs which don't support JVMCI we have to use the more specific `(WB.getBooleanVMFlag("EnableJVMCI") != null)`.
>> 
>> Please let me know if you want me to push this instantly after it has been reviewed or if you first want to re-run your internal Tier3 tests before pushing.
>
> Looks good! I guess it does not hurt to quickly verify it. Tier3 testing is submitted, will get back to you with the results.

Thanks @chhagedorn, @TobiHartmann!

I'll wait with submitting until @chhagedorn reports back the Tier3 results.

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PR: https://git.openjdk.java.net/jdk/pull/6581