The GraalVM compiler is a dynamic compiler written in Java that integrates with the HotSpot JVM. It has a focus on high performance and extensibility. In addition, it provides optimized performance for languages implemented with Truffle Framework-based languages running on the JVM. For brevity, the GraalVM compiler is often referred to as "the compiler" below.

Working with the GraalVM compiler will mean cloning more than one repository and so it's recommended to create and use a separate directory:

$ mkdir graal
$ cd graal

To simplify development, a separate Python tool called mx has been co-developed. This tool must be downloaded and put onto your PATH:

$ git clone https://github.com/graalvm/mx.git
$ export PATH=$PWD/mx:$PATH

The compiler depends on a JDK that supports a compatible version of JVMCI (JVM Compiler Interface). There is a JVMCI port for JDK 8 and the required JVMCI version is built into the JDK as of JDK 11. A JVMCI-enabled JDK 8 can be downloaded from GitHub or you can build it yourself.

The JVMCI JDKs that Graal is currently tested against are specified in common.json.

Most compiler sources are compliant with Java 8. Some sources use API specific to JDK 8 or only introduced in JDK 9. These sources are in versioned projects. If you don't have a JDK that satisfies the requirement of a versioned project, the project is ignored by mx.

If you want to develop on a single JDK version, you only need to define JAVA_HOME. For example:

$ export JAVA_HOME=/usr/lib/jvm/oraclejdk1.8.0_212-jvmci-20-b01

or:

$ export JAVA_HOME=/usr/lib/jvm/jdk-11

If you want to ensure your changes will pass both JDK 8 and JDK 11 gates, you can specify the secondary JDK(s) in EXTRA_JAVA_HOMES. For example, to develop for JDK 8 while ensuring mx build still works with the JDK 11 specific sources:

$ export JAVA_HOME=/usr/lib/jvm/oraclejdk1.8.0_212-jvmci-20-b01
$ export EXTRA_JAVA_HOMES=/usr/lib/jvm/jdk-11

And on macOS:

$ export JAVA_HOME=/Library/Java/JavaVirtualMachines/oraclejdk1.8.0_212-jvmci-20-b01/Contents/Home
$ export EXTRA_JAVA_HOMES=/Library/Java/JavaVirtualMachines/jdk-11.jdk/Contents/Home

If you omit EXTRA_JAVA_HOMES in the above examples, versioned projects depending on the specified JDK(s) will be ignored. Note that JAVA_HOME defines the primary JDK for development. For instance, when running mx vm, this is the JDK that will be used so if you want to run on JDK 11, swap JDK 8 and JDK 11 in JAVA_HOME and EXTRA_JAVA_HOMES.

Now change to the graal/compiler directory:

$ cd graal/compiler

Changing to the graal/compiler directory informs mx that the focus of development (called the primary suite) is the GraalVM compiler. All subsequent mx commands should be executed from this directory.

Here's the recipe for building and running the GraalVM compiler:

$ mx build
$ mx vm

When running mx vm, the GraalVM compiler is used as the top tier JIT compiler by default. To revert to using C2 instead, add the -XX:-UseJVMCICompiler option to the command line. To disable use of the GraalVM compiler altogether (i.e. for hosted compilations as well), use -XX:-EnableJVMCI.

When applying above steps on Windows, replace export with set.

You can generate IDE project configurations by running:

$ mx ideinit

This will generate Eclipse, IntelliJ, and NetBeans project configurations. Further information on how to import these project configurations into individual IDEs can be found on the IDEs page.

The Ideal Graph Visualizer(IGV) is very useful in terms of visualizing the compiler's intermediate representation (IR). IGV is available on OTN. You can get a quick insight into this tool by running the commands below. The first command launches the tool and the second runs one of the unit tests included in the code base with extra options to dump the compiler IR for all methods compiled. You should wait for the GUI to appear before running the second command.

$ $GRAALVM_EE_HOME/bin/idealgraphvisualizer &
mx unittest -Djdk.graal.Dump BC_athrow0

If you added -XX:+UseJVMCICompiler as described above, you will see IR for compilations requested by the VM itself in addition to compilations requested by the unit test. The former are those with a prefix in the UI denoting the compiler thread and id of the compilation (e.g., JVMCI CompilerThread0:390).

Further information can be found on the Debugging page.

Building the GraalVM compiler as described above means it is executed in the same way as any other Java code in the VM; it allocates in the HotSpot heap and it starts execution in the interpreter with hot parts being subsequently JIT compiled. The advantage of this mode is that it can be debugged with a Java debugger.

However, it has some disadvantages. Firstly, since it uses the object heap, it can reduce application object locality and increase GC pause times. Additionally, it can complicate fine tuning options such as -Xmx and -Xms which now need to take the heap usage of the compiler into account. Secondly, the compiler will initially be executed in the interpreter and only get faster over time as its hot methods are JIT compiled. This is mitigated to some degree by forcing the GraalVM compiler to only be compiled by C1 (i.e., -Djdk.graal.CompileGraalWithC1Only=true) but this comes at the cost of slower compilation speed.

To address these issues, the GraalVM compiler can be deployed as a native shared library. The shared library is a native image produced using SubstrateVM. In this mode, the GraalVM compiler uses memory separate from the HotSpot heap and it runs compiled from the start. That is, it has execution properties similar to other native HotSpot compilers such as C1 and C2.

To build libgraal:

$ cd graal/vm
$ mx --env libgraal build

The newly built GraalVM image containing libgraal is available at:

$ mx --env libgraal graalvm-home

or following this symlink:

$ ./latest_graalvm_home

For more information about building GraalVM images, see the README file of the vm suite.

Without leaving the graal/vm directory, you can now run libgraal as follows:

1. Use the GraalVM image that you just built:

   $ ./latest_graalvm_home/bin/java -XX:+UseJVMCICompiler -XX:+UseJVMCINativeLibrary ...

2. Use mx:

   • On linux:

     $ mx -p ../compiler vm -XX:JVMCILibPath=latest_graalvm_home/jre/lib/amd64 -XX:+UseJVMCICompiler -XX:+UseJVMCINativeLibrary ...

   • On macOS:

     $ mx -p ../compiler vm -XX:JVMCILibPath=latest_graalvm_home/jre/lib -XX:+UseJVMCICompiler -XX:+UseJVMCINativeLibrary ...

For video tutorials, presentations and publications on the GraalVM compiler visit the Publications page.

For instructions for building a JVMCI enabled JDK 8, refer to the graal-jvmci-8 repository.

The GraalVM compiler is licensed under the GPL 2.