RFR: 8309136: [JVMCI] add -XX:+UseGraalJIT flag [v3]

[Doug Simon]

On Wed, 31 May 2023 23:26:17 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. It is an alias for `-XX:+EnableJVMCIProduct -Djvmci.Compiler=graal`. 
>> 
>> When `-XX:+UseGraalJIT` is specified, 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 five additional commits since the last revision:
> 
>  - improve error message when UseGraalJIT is used without -XX:+UnlockExperimentalVMOptions
>  - use strncmp instead of strcmp
>  - fix date in copyright header
>  - set UseGraalJIT value in enable_jvmci_product_mode
>  - added missing test of UseJVMCICompiler when adjusting JVMCI flags under -Xint

Thanks for input David. I agree that it's best to open a new JBS issue to discuss concerns about lazy JVMCI compiler initialization.

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PR Comment: https://git.openjdk.org/jdk/pull/14231#issuecomment-1571577103