RFR: 8345826: Do not automatically resolve jdk.internal.vm.ci when libgraal is used [v3]

[Ioi Lam]

On Fri, 16 May 2025 15:26:31 GMT, Doug Simon <dnsimon at openjdk.org> wrote:

>> I ran a recent build of Oracle JDK 25 that has libjvmcicompiler.so (not including your changes):
>> 
>> 
>> $ ./bin/java -XX:+UnlockExperimentalVMOptions -XX:+UseGraalJIT -XX:+PrintFlagsFinal --version | \
>>         egrep '(EnableJVMCI)|(UseJVMCICompiler)|(UseJVMCINativeLibrary)'
>>      bool EnableJVMCI           = true    {JVMCI product} {default}
>>      bool EnableJVMCIProduct    = true    {JVMCI product} {command line}
>>      bool UseJVMCICompiler      = true    {JVMCI product} {default}
>>      bool UseJVMCINativeLibrary = true    {JVMCI product} {default}
>> $ ./bin/java -XX:+UnlockExperimentalVMOptions -XX:+EnableJVMCI -XX:+PrintFlagsFinal --version | \
>>         egrep '(EnableJVMCI)|(UseJVMCICompiler)|(UseJVMCINativeLibrary)'
>>      bool EnableJVMCI           = true    {JVMCI experimental} {command line}
>>      bool EnableJVMCIProduct    = false   {JVMCI experimental} {default}
>>      bool UseJVMCICompiler      = false   {JVMCI experimental} {default}
>>      bool UseJVMCINativeLibrary = true    {JVMCI experimental} {default}
>> 
>> 
>> So If you specify only `-XX:+EnableJVMCI` in the command-line, `UseJVMCINativeLibrary` will be true. As a result, with your latest version, the `jdk.internal.vm.ci` module is not added.
>> 
>> If you have an app that wants to use the jdk.internal.vm.ci API, you must specify both `-XX:+EnableJVMCI` and `
>>  --add-modules=jdk.internal.vm.ci`. Is this intentional?
>
>> If you have an app that wants to use the jdk.internal.vm.ci API, you must specify both -XX:+EnableJVMCI and  --add-modules=jdk.internal.vm.ci.
> 
> You should only have to specify `--add-modules=jdk.internal.vm.ci` and that now sets `+EnableJVMCI`. If you also want libgraal to be used as the JIT (instead of C2), then you need to add `-XX:+UseGraalJIT`.
> 
> For the Truffle on Oracle JDK, this means:
> * `--add-modules=jdk.internal.vm.ci`: Use C2 for JIT ("hosted") compilation and libgraal for Truffle ("guest") compilation
> * `--add-modules=jdk.internal.vm.ci -XX:+UseGraalJIT`: Use libgraal for both JIT and Truffle compilation

Ah I forgot the setting on EnableJVMCI to true. Thanks for the explanation.

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

PR Review Comment: https://git.openjdk.org/jdk/pull/25240#discussion_r2093283370