cgsdfc / simplecc

A simple and modular C-like compiler in C++ for educational purposes.

A simple and modular C-like compiler in C++

1. Source language

This project is a small compiler written in modern C++ for education and practice. The source language it compiles is called C0, which is a modified subset of C for educational purposes. The BNF grammar rules of C0 can be found in the file Grammar. In brief, this tiny language consists of the following components:

1. Constant declarations, like const int a = 1, f = 2;
2. Variable declarations, like char b; int c;
3. Function definitions, like void func() {}
4. Some C-like statements and expressions.

The test/ folder contains some vivid examples of the C0 language (files with .c0 suffix).

2. Supported backends

2.1 Mips Assembly

We have a hand-rolled stack-based IR generator that emits unoptimized Mips assembly, which can be executed by the Mars simulator. To use this backend, please run:

simplecc --asm input.c0

For more examples of the emitted Mips assembly

2.2 LLVM IR

We also integrate with the LLVM backend to enjoy its capacities of optimization and native codegen. To obtain an LLVM IR file, please run:

simplecc --emit-llvm input.c0

For more examples of emitted IR, please see the *.ll files in test/LLVM/ir/.

To obtain a native executable, please run:

simplecc --emit-llvm | clang -x ir

3. Visualization & debug support

We provide some support to inspect the intermediate results of the compiler.

3.1 Tokens

To see a stream of tokens, please run:

simplecc --print-tokens input.c0

This will print details about the tokens extracted from the source (one token in a line).

3.2 AST

To pretty-print the AST of the program, please run:

simplecc --print-ast input.c0

To obtain a flowchart of the AST, a graphviz-based diagram of AST can be generated with:

simplecc --ast-graph input.c0

This command will generate a dot file, which can be passed to the command dot as follows:

simplecc --ast-graph input.c0 | dot -Tpng -o input.png

3.3 Syntax checking

To check the syntax of a source file (but not emitting anything), please run:

simplecc --check-only input.c0

This will print any detected errors to the console.

4. Build & Install

This project requires a modern compiler that supports C++11. Please run the following commands to build and install our executable:

cd simplecc/ && mkdir -p build/
cd build/ && cmake -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX=$HOME ../src
make && make install

The command simplecc will then be available.

5. Optimization

For simplicity, we do not implement too many optimization passes. Only simple constant folding and dead code elimination are implemented. Please see src/lib/Transform for more details.

6. Citation

If you use our code in your research, we highly recommend your proper citation as follows:

@misc{cong_simplecc_2018,
	title = {Simplecc: {A} simple and modular {C}-like compiler in {C}++},
	shorttitle = {Simplecc},
	url = {https://github.com/cgsdfc/simplecc.git},
	abstract = {Simplecc is a small compiler written in modern C++ that compiles an educational C-like language C0. It has a primary backend that emits stack-based unoptimized Mips assembly. It also integrates with an external LLVM backend that enables optimization and native codegen. Internally it uses a generated parser and generated abstract syntax tree with other important components written in an object-oriented style.},
	author = {Cong Feng},
	year = {2018},
}