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Graal 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 Truffle-based languages running on the JVM.


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

mkdir graal
cd graal

Building Graal

To simplify Graal 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

Graal 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. To develop Graal you need either a JVMCI-enabled JDK 8 (download from OTN or build yourself) or JDK 11 (build 20 or later).

Most Graal 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 only want to develop Graal for a single JDK version, you only need to define JAVA_HOME. For example:

export JAVA_HOME=/usr/lib/jvm/labsjdk1.8.0_172-jvmci-0.46


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 Graal for JDK 8 while ensuring mx build still works with the JDK 11 specific sources:

export JAVA_HOME=/usr/lib/jvm/labsjdk1.8.0_172-jvmci-0.46
export EXTRA_JAVA_HOMES=/usr/lib/jvm/jdk-11

And on macOS:

export JAVA_HOME=/Library/Java/JavaVirtualMachines/labsjdk1.8.0_172-jvmci-0.46/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 Graal. All subsequent mx commands should be executed from this directory.

Here's the recipe for building and running Graal (if on Windows, replace mx with mx.cmd):

mx build
mx vm

By default, Graal is only used for hosted compilation (i.e., the VM still uses C2 for compilation). To make the VM use Graal as the top tier JIT compiler, add the -XX:+UseJVMCICompiler option to the command line. To disable use of Graal altogether, use -XX:-EnableJVMCI.

IDE Configuration

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 Graal code base includes the Ideal Graph Visualizer which is very useful in terms of visualizing Graal's intermediate representation (IR). 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 Graal code base with extra options to make Graal dump the IR for all methods it compiles. You should wait for the GUI to appear before running the second command.

mx igv &
mx unittest -Dgraal.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.

Publications and Presentations

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

Building JVMCI JDK 8

To create a JVMCI enabled JDK 8 on other platforms (e.g., Windows):

git clone https://github.com/graalvm/graal-jvmci-8
cd graal-jvmci-8
mx --java-home /path/to/jdk8 build
mx --java-home /path/to/jdk8 unittest
export JAVA_HOME=$(mx --java-home /path/to/jdk8 jdkhome)

You need to use the same JDK the OTN downloads are based on as the argument to --java-home in the above commands. The build step above should work on all supported JDK 8 build platforms. It should also work on other platforms (such as Oracle Linux, CentOS and Fedora as described here). If you run into build problems, send a message to the Graal mailing list.


The Graal compiler is licensed under the GPL 2.