# Melior

[![GitHub Action](https://img.shields.io/github/actions/workflow/status/raviqqe/melior/test.yaml?branch=main&style=flat-square)](https://github.com/raviqqe/melior/actions?query=workflow%3Atest)
[![Crate](https://img.shields.io/crates/v/melior.svg?style=flat-square)](https://crates.io/crates/melior)
[![License](https://img.shields.io/github/license/raviqqe/melior.svg?style=flat-square)](https://github.com/raviqqe/melior/blob/main/LICENSE)

Melior is the MLIR bindings for Rust. It aims to provide a simple,
safe, and complete API for MLIR with a reasonably sane ownership model
represented by the type system in Rust.

This crate is a wrapper of [the MLIR C API](https://mlir.llvm.org/docs/CAPI/).

## Examples

### Building a function to add integers

```rust
use melior::{
    Context,
    dialect::{arith, DialectRegistry, func},
    ir::{*, attribute::{StringAttribute, TypeAttribute}, r#type::FunctionType},
    utility::register_all_dialects,
};

let registry = DialectRegistry::new();
register_all_dialects(&registry);

let context = Context::new();
context.append_dialect_registry(&registry);
context.load_all_available_dialects();

let location = Location::unknown(&context);
let module = Module::new(location);

let index_type = Type::index(&context);

module.body().append_operation(func::func(
    &context,
    StringAttribute::new(&context, "add"),
    TypeAttribute::new(FunctionType::new(&context, &[index_type, index_type], &[index_type]).into()),
    {
        let block = Block::new(&[(index_type, location), (index_type, location)]);

        let sum = block.append_operation(arith::addi(
            block.argument(0).unwrap().into(),
            block.argument(1).unwrap().into(),
            location
        ));

        block.append_operation(func::r#return( &[sum.result(0).unwrap().into()], location));

        let region = Region::new();
        region.append_block(block);
        region
    },
    &[],
    location,
));

assert!(module.as_operation().verify());
```

## Install

```sh
cargo add melior
```

### Dependencies

[LLVM/MLIR 17](https://llvm.org/) needs to be installed on your system. On Linux and macOS, you can install it via [Homebrew](https://brew.sh).

```sh
brew install llvm@17
```

## Documentation

On [GitHub Pages](https://raviqqe.github.io/melior/melior/).

## Contribution

Contribution is welcome! But, Melior is still in the alpha stage as well as the MLIR C API. Note that the API is unstable and can have breaking changes in the future.

### Technical notes

- We always use `&T` for MLIR objects instead of `&mut T` to mitigate the intricacy of representing a loose ownership model of the MLIR C API in Rust.
- Only UTF-8 is supported as string encoding.
  - Most string conversion between Rust and C is cached internally.

### Naming conventions

- `Mlir<X>` objects are named `<X>` if they have no destructor. Otherwise, they are named `<X>` for owned objects and `<X>Ref` for borrowed references.
- `mlir<X>Create` functions are renamed as `<X>::new`.
- `mlir<X>Get<Y>` functions are renamed as follows:
  - If the resulting objects refer to `&self`, they are named `<X>::as_<Y>`.
  - Otherwise, they are named just `<X>::<Y>` and may have arguments, such as position indices.

### Safety

Although Melior aims to be completely type safe, some part of the current API is
not.

- Access to operations, types, or attributes that belong to dialects not
  loaded in contexts can lead to runtime errors or segmentation faults in
  the worst case.
  - Fix plan: Load all dialects by default on creation of contexts, and
    provide unsafe constructors of contexts for advanced users.
- IR object references returned from functions that move ownership of
  arguments might get invalidated later.
  - This is because we need to borrow `&self` rather than `&mut self` to
    return such references.
  - e.g. `Region::append_block()`
  - Fix plan: Use dynamic check, such as `RefCell`, for the objects.

## References

- The raw C binding generation depends on [femtomc/mlir-sys](https://github.com/femtomc/mlir-sys).
- The overall design is inspired by [TheDan64/inkwell](https://github.com/TheDan64/inkwell).

## License

[Apache 2.0](https://github.com/raviqqe/melior/blob/main/LICENSE)