marcospb19 / mini-c

My first try at writing a LLVM compiler

mini-c

My (initial) experiments building compilers with LLVM.

Examples:

int fibonacci(int n) {
  if (n <= 1) {
    return 1;
  }
  return fibonacci(n - 2) + fibonacci(n - 1);
}

int factorial(int n) {
  if (n <= 1) {
    return 1;
  }
  return n * factorial(n - 1);
}

How

I'm generating LLVM-IR using inkwell, it's the only decent library I found.

After generating the IR, there are two options:

1. Running in LLVM's JIT execution engine (commented out in the code).
2. Dumping the IR into a file and using several utils to create the final binary.

I'm doing the latter, which is cumbersome but let's me inspect the generated assembly.

Here's the huge command I'm running:

clear \
    && cargo run -- file.c \
    && llc llvm-ir.ll -o assembly.s \
    && clang assembly.s -o a.out \
    && bat file.c \
    && (./a.out ; echo "\$? = $?")

Here's the oneliner:

clear && cargo run -- file.c && llc llvm-ir.ll -o assembly.s && clang assembly.s -o a.out && bat file.c && (./a.out ; echo "\$? = $?")

1. My program compiles file.c to LLVM IR and dumps it to the file llvm-ir.ll.
2. llc compiles llvm-ir.ll into the assembly file assembly.s.
3. clang compiles assembly.s into machine-code, a.out.
4. Show the source code, run the program (output appears here) and then print the return code.

You need llvm installed for lcc and clang.

You can also use gcc instead of clang here.

Dependencies for building

If you try running cargo run you'll meet a unpleasant linking error.

In some systems, installing llvm may solve, in Arch Linux you need to download a LLVM release tarball and unpack it.

https://github.com/llvm/llvm-project/releases/tag/llvmorg-15.0.0

Then point an env var to the resulting folder like so:

export LLVM_SYS_150_PREFIX=$(realpath ../llvm/clang+llvm-15.0.0-x86_64-linux-gnu-rhel-8.4)

Now llvm-sys and inkwell will compile fine, make sure you open your text editor of choice after setting this env var.