georgesittas / minijava-compiler

MiniJava to LLVM IR compiler

MiniJava Compiler

This is a MiniJava compiler that targets LLVM, written in Java with the help of JFlex, JavaCUP and JTB.

I would like to thank Stefanos Baziotis for contributing his MiniJava testsuite!

Usage

# Compile the project
make

# Run the compiler
java Main file1 [file2 [file3 ...]]

# Cleanup
make clean

Implementation

Scoping & Symbol Table

MiniJava is a simple language when it comes to scoping: all declarations precede statements. This property prevents declarations from showing up in nested compound statements such as if-else, while and block statements. Thus, the symbol table need only keep track of class declarations, class-scoped declarations (i.e. fields and methods) and method-scoped declarations (i.e. formal parameters and local variables).

Compilation Phases

We start by producing an AST for the source program with the help of JFlex, JavaCUP and JTB. Then, we check its semantics & finally generate the LLVM IR code with the help of the following visitor classes:

1. STVisitor populates the symbol table

2. SCVisitor type checks the program

3. VTVisitor populates the virtual method table

4. CGVisitor generates the resulting LLVM IR code

Notes

• The MainClass class and its main method are not handled as special cases. The method's argument is stored in the symbol table with type String[], so, if it appears in any expression in the program, a type error will be triggered by SCVisitor inevitably.

• Scopes are implemented by constructing strings of the form ClassID [":" [MethodID]] and passing them as arguments to children nodes as the visitors are walking the AST.

• LLVM-IR code virtual registers are assigned names of the form %_number, where number is an auto-incrementing integer.