Summary

Add -XX:+UseGraalJIT VM experimental flag to select the Graal-based JIT in the JDK image as the top tier JIT.

Problem

Introducing a -XX:+UseGraalJIT flag simplifies the command line for users wishing to use the Graal JIT embedded in a JDK image. The current flag for selecting the Graal JIT is:

-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 have equated JVMCI with Graal.

Solution

Define a -XX:+UseGraalJIT flag to simplify and secure the selection of the Graal JIT.

Specification

The -XX:+UseGraalJIT flag would be defined as an alias for:

-XX:+EnableJVMCIProduct -Djvmci.Compiler=graal

Including -Djvmci.Compiler=graal in the alias expansion means there will be a clear and fast failure if the JDK image contains no JVMCI implementation or a non-Graal JVMCI implementation.