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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.

Install LLVM Runtime

Since GraalVM 22.2, the LLVM runtime is packaged in a separate GraalVM component. It can be installed with GraalVM Updater:

$GRAALVM_HOME/bin/gu install llvm

This installs GraalVM’s implementation of lli in the $GRAALVM_HOME/bin directory. With the LLVM runtime installed, you can execute programs in LLVM bitcode format on GraalVM.

Additionally to installing the LLVM runtime, you can add the LLVM toolchain:

gu install llvm-toolchain
export LLVM_TOOLCHAIN=$(lli --print-toolchain-path)

Now you can compile C/C++ code to LLVM bitcode using clang shipped with GraalVM via a prebuilt 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