Kefir: An Independent C17/C23 Compiler

Kefir is a unique compiler for the C17 and C23 programming languages, crafted by Jevgenij Protopopov. It stands out for its comprehensive support of the C standards, including complex numbers and bit-precise integers, and its compatibility with various Unix-like systems such as Linux and BSD variants. The compiler is validated through a rigorous test suite encompassing 100 software projects, ensuring its robustness and reliability.

## Features and Capabilities

Kefir supports a wide array of features from the C17 and C23 standards, including variable-length arrays and _Decimal floating-point numbers. It is designed to integrate seamlessly with existing system toolchains, supporting both GNU As and Yasm assemblers, and provides a cc-compatible command line interface. The compiler is written in C11, minimizing runtime dependencies to the standard library and some POSIX components.

## Optimization and Code Generation

The compiler employs an SSA-based optimization pipeline, focusing on local scalars and offering optimizations like constant folding and loop-invariant code motion. It supports DWARF5 debug information and generates position-independent code. Kefir's optimization pipeline is structured along abstraction levels, ensuring efficient code generation and transformation.

## Testing and Validation

Kefir undergoes extensive testing, including its own test suite and external test suites like c-testsuite and GCC Torture suite. These tests validate the compiler's functionality across various platforms, ensuring compatibility and performance. The compiler also supports a reproducible bootstrap process, demonstrating its ability to produce identical copies of itself.

## Installation and Usage

Building Kefir requires a C11 compiler, GNU Make, and other standard tools. It can be installed via make on supported platforms, with detailed instructions provided for different environments. The compiler's dependencies include an external assembler and linker, with specific requirements for atomic operations and decimal floating-point support.

## Limitations and Considerations

While Kefir is a robust compiler, it is developed by a single individual without external funding, which may limit its support in production environments. The author acknowledges potential bugs and encourages feedback for improvements. Compatibility with C23 features is still evolving, with the majority of external validations focusing on C17.

## Future Prospects

The project has seen several releases since its inception in 2020, with continuous improvements in optimization and feature support. Future development is uncertain, but the author remains committed to maintaining and refining the compiler as needed.

## Licensing and Contribution

Kefir is licensed under GNU GPLv3, with runtime headers under BSD-3 terms. Contributions are welcome, but non-trivial code changes require prior discussion with the author. The project is distributed as source code, with release tarballs available on the project's website.