roc/compiler/builtins/bitcode

Bitcode for Builtins

Roc's builtins are implemented in the compiler using LLVM only. When their implementations are simple enough (e.g. addition), they can be implemented directly in Inkwell.

When their implementations are complex enough, it's nicer to implement them in a higher-level language like Rust, compile the result to LLVM bitcode, and import that bitcode into the compiler.

Here is the process for doing that.

Building the bitcode

The source we'll use to generate the bitcode is in src/lib.rs in this directory.

To generate the bitcode, cd into compiler/builtins/bitcode/ and run:

$ cargo rustc --release --lib -- --emit=llvm-bc

Then look in the root roc source directory under target/release/deps/ for a file with a name like roc_builtins_bitcode-8da0901c58a73ebf.bc - except probably with a different hash before the .bc. If there's more than one *.bc file in that directory, delete the whole deps/ directory and re-run the cargo rustc command above to regenerate it.

If you want to take a look at the human-readable LLVM IR rather than the bitcode, run this instead and look for a .ll file instead of a .bc file:

$ cargo rustc --release --lib -- --emit=llvm-ir

Importing the bitcode

The bitcode is a bunch of bytes that aren't particularly human-readable. Since Roc is designed to be distributed as a single binary, these bytes need to be included in the raw source somewhere.

The llvm/src/build.rs file statically imports these raw bytes using the include_bytes! macro, so we just need to move the .bc file from the previous step to the correct location.

The current .bc file is located at:

compiler/gen/src/llvm/builtins.bc

...so you want to overwrite it with the new .bc file in target/deps/

Once that's done, git status should show that the builtins.bc file has been changed. Commit that change and you're done!