add contibuting.md

Author: g4titanx

CONTRIBUTING.md

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+# Contributing to rust_codegen_gcc
+
+Welcome to the rust_codegen_gcc project! This guide will help you get started as a contributor. The project aims to provide a GCC codegen backend for rustc, allowing Rust compilation on platforms unsupported by LLVM and potentially improving runtime performance through GCC's optimizations.
+
+## Getting Started
+
+### Setting Up Your Development Environment
+
+1. Install the required dependencies:
+   - rustup (follow instructions on the [official website](https://rustup.rs))
+   - DejaGnu (for running libgccjit test suite)
+   - Additional packages: `flex`, `libmpfr-dev`, `libgmp-dev`, `libmpc3`, `libmpc-dev`
+
+2. Clone and configure the repository:
+   ```bash
+   git clone https://github.com/rust-lang/rust_codegen_gcc
+   cd rust_codegen_gcc
+   cp config.example.toml config.toml
+   ```
+
+3. Build the project:
+   ```bash
+   ./y.sh prepare  # downloads and patches sysroot
+   ./y.sh build --sysroot --release
+   ```
+
+### Running Tests
+
+To verify your setup:
+```bash
+# Run the full test suite
+./y.sh test --release
+
+# Test with a simple program
+./y.sh cargo build --manifest-path tests/hello-world/Cargo.toml
+```
+
+## Communication Channels
+
+- Matrix: Join our [Matrix channel](https://matrix.to/#/#rustc_codegen_gcc:matrix.org)
+- IRC: Join us on [IRC](https://web.libera.chat/#rustc_codegen_gcc)
+- GitHub Issues: For bug reports and feature discussions
+
+We encourage new contributors to join our communication channels and introduce themselves. Feel free to ask questions about where to start or discuss potential contributions.
+
+## Understanding Core Concepts
+
+### Project Structure
+
+The project consists of several key components:
+- The GCC backend integration through libgccjit
+- Rust compiler interface
+- Test infrastructure
+
+### Common Development Tasks
+
+#### Running Specific Tests
+To run a specific test:
+1. Individual test: `./y.sh test --test <test_name>`
+2. libgccjit tests: 
+   ```bash
+   cd gcc-build/gcc
+   make check-jit
+   # For a specific test:
+   make check-jit RUNTESTFLAGS="-v -v -v jit.exp=jit.dg/test-asm.cc"
+   ```
+
+#### Debugging Tools
+The project provides several environment variables for debugging:
+- `CG_GCCJIT_DUMP_MODULE`: Dumps a specific module
+- `CG_GCCJIT_DUMP_TO_FILE`: Creates C-like representation
+- `CG_GCCJIT_DUMP_RTL`: Shows Register Transfer Language output
+
+Full list of debugging options can be found in the README.
+
+## Making Contributions
+
+### Finding Issues to Work On
+1. Look for issues labeled with `good-first-issue` or `help-wanted`
+2. Check the project roadmap for larger initiatives
+3. Consider improving documentation or tests
+
+### Pull Request Process
+1. Fork the repository and create a new branch
+2. Make your changes with clear commit messages
+3. Add tests for new functionality
+4. Update documentation as needed
+5. Submit a PR with a description of your changes
+
+### Code Style Guidelines
+- Follow Rust standard coding conventions
+- Ensure your code passes `rustfmt` and `clippy`
+- Add comments explaining complex logic, especially in GCC interface code
+
+## Additional Resources
+
+- [Rustc Dev Guide](https://rustc-dev-guide.rust-lang.org/)
+- [GCC Internals Documentation](https://gcc.gnu.org/onlinedocs/gccint/)
+- Project-specific documentation in the `doc/` directory:
+  - Common errors
+  - Debugging GCC LTO
+  - Git subtree sync
+  - Sending patches to GCC
+
+## Getting Help
+
+If you're stuck or unsure about anything:
+1. Check the existing documentation in the `doc/` directory
+2. Ask in the IRC or Matrix channels
+3. Open a GitHub issue for technical problems
+4. Comment on the issue you're working on if you need guidance
+
+Remember that all contributions, including documentation improvements, bug reports, and feature requests, are valuable to the project.