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

[Vladimir Kozlov]

On Wed, 31 May 2023 08:08:34 GMT, Doug Simon <dnsimon at openjdk.org> wrote:

>> Use of the Graal-based JIT in OpenJDK currently requires the following flag: `-XX:+EnableJVMCIProduct`
>> 
>> This has no direct association with Graal. If the JDK image happens to include a non-Graal JVMCI implementation, it will be automatically selected. This would come as a surprise to users who equate JVMCI with Graal.
>> 
>> This PR introduces a new flag, `-XX:+UseGraalJIT` to address these shortcomings. The VM fails fast at startup if there is a non-Graal JVMCI implementation or no JVMCI implementation in the JDK image.
>
> Doug Simon has updated the pull request incrementally with one additional commit since the last revision:
> 
>   review based fixes

What about `UseJVMCICompiler` flag? A lot of code in HotSpot is guarded by this flag.

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PR Review: https://git.openjdk.org/jdk/pull/14231#pullrequestreview-1453927961