GraalVM LLVM Runtime

The GraalVM LLVM runtime can execute programming languages that can be transformed to LLVM bitcode. This includes languages like C/C++, Fortran and others.

In contrast to static compilation that is normally used for LLVM-based languages, GraalVM’s implementation of the lli tool first interprets LLVM bitcode and then dynamically compiles the hot parts of the program using the Graal compiler. This allows seamless interoperability with the dynamic languages supported by GraalVM.

Getting Started #

As of GraalVM for JDK 21, the GraalVM LLVM runtime is available as a standalone distribution. You can download a standalone based on Oracle GraalVM or GraalVM Community Edition.

  1. Download the LLVM standalone for your operating system:
  2. Unzip the archive:
    tar -xzf <archive>.tar.gz

    Alternatively, open the file in the Finder.

    Note: If you are using macOS Catalina and later you may need to remove the quarantine attribute:

     sudo xattr -r -d <archive>.tar.gz
  3. A standalone comes with a JVM in addition to its native launcher. Check the version to see GraalVM LLVM runtime is active:
     ./path/to/bin/lli --version

Now you can execute programs in the LLVM bitcode format.

LLVM Toolchain #

Additionally, a prebuilt LLVM toolchain is bundled with the GraalVM LLVM runtime.

  1. Get the location of the toolchain, using the --print-toolchain-path argument of lli:
     ./path/to/bin/lli --print-toolchain-path
  2. Set the LLVM_TOOLCHAIN environment variable:
     export LLVM_TOOLCHAIN=$(./path/to/bin/lli --print-toolchain-path)
  3. Then see the content of the toolchain path for a list of available tools:

Now you can compile C/C++ code to LLVM bitcode using clang shipped with GraalVM via the LLVM toolchain.

Run LLVM Bitcode on GraalVM #

To run LLVM-based languages on GraalVM, the binaries need to be compiled with embedded bitcode. The Compiling guide provides information on how to compile a program to LLVM bitcode and what file format is expected.

The syntax to execute programs in LLVM bitcode format on GraalVM is:

lli [LLI options] [GraalVM options] [polyglot options] <bitcode file> [program args]

Here, <bitcode file> is a compiled program with embedded LLVM bitcode. See LLI Command Options or use lli --help for options explanations.

For example, put this C code into a file named hello.c:

#include <stdio.h>

int main() {
    printf("Hello from GraalVM!\n");
    return 0;

Then compile hello.c to an executable hello with embedded LLVM bitcode and run it as follows:

$LLVM_TOOLCHAIN/clang hello.c -o hello
lli hello

Note: LLVM bitcode is platform-dependent. The program must be compiled to bitcode for an appropriate platform.

Further Reading #

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