Code Generator for C/C++

Programming Language Technology Course, 2014, Laboration 3
Aarne Ranta (aarne (at)


14/3 Updates about test script by John Camilleri.

25/2 There is now an automatic test script in the testsuite directory.

24/2 The minimum test suite to pass is the same "good" directory as has been used to get started. If you are ambitious, you can also try the good files in lab2 testsuite. The big difference is whether instructions of type Double are needed.

18/2/2014 Some new advice and links to supporting material - look for boldfaced paragraphs below. In particular, the mini folders now contain compiler code and Readme files for this purpose.


The objective of this assignment is to write a code generator from a fragment of the C++ programming language to JVM, Java Virtual Machine. The code generator should produce Java class files, which can be run in the Java bytecode interpreter so that they correctly perform all their input and output actions.

Before the work can be submitted, the program has to pass some tests, which are given on the course web page via links later in this document.

Since this lab assumes a type checker, it is enough to run the tests in the "good" directory.

The recommended implementation is via a BNF grammar processed by the BNF Converter (BNFC) tool. The syntax tree created by the parser is first type checked by using the type checker created in Lab 2. The code generator should then make another pass of the type-checked code.

The type checker is moreover recommended to annotate the abstract syntax trees with types, needed in instruction selection.

However, it is probably a good idea to start with the lab2 type checker as it is. Then one can get straight into the business of code generation.

The approximate size of the grammar is 50 rules, and the code generator should be 100-300 lines, depending on the programming language used.

All BNFC supported languages can be used, but guidance is guaranteed only for Haskell and Java.

The code generator is partially characterized by compilation schemes in Chapter 6 of the PLT book. More JVM instructions are given in Appendix B. These explanations follow Jasmin assembler; the code generator may emit Jasmin assembly code into text files, which are then processed further by Jasmin to create class files.

Jasmin can be downloaded here.


The recommended procedure is two passes:

  1. build a symbol table that for every function gives its type in a form usable for JVM code generation;
  2. compile the program by generating a class file containing every source code function as a method.

You can copy your grammar and the TypeChecker module from Lab 2 to the same directory.

Language specification

The language is the same as in Lab 2, and you can use the grammar file Also its type system is the same.

There are four built-in functions:

    void   printInt(int x)        // print an integer and a newline in standard output
    void   printDouble(double x)  // print a double and a newline in standard output
    int    readInt()              // read an integer from standard input
    double readDouble()           // read a double from standard input

These functions can be defined in a separate runtime class, which can be obtained e.g. from writing these functions in Java and compiling to a class file.

A ready-made Java file is here.

Class structure

Boilerplate code, see PLT book, Chapter 6.


Methods in the class, main special, see Chapter 6.

Statements and expressions

The semantics is the same as in Lab 3. In other words, running the generated classes in java produces the same behaviour as running the source code in the lab2 interpreter.

Solution format

Input and output

The code generator must be a program called lab3, which is executed by the command

    lab3 <SourceFile>

and produces a class (.class) file. It may do this by first generating Jasmin assembly code (a .j file) and then calling Jasmin on this code. Jasmin can be called by

    java -jar jasmin.jar <File>.j

The generated class file should have the same name and be in the same directory as the original source file:

    lab3 ../a/b/

This should produce a class file ../a/b/c.class.

The output at failure is a code generator error, or a TYPE ERROR as in Assignment 2, or a SYNTAX ERROR as in Assignment 1.

The input can be read not only from user typing on the terminal, but also from standard input redirected from a file or by echo. For instance,

    ./java fibonacci <test-input
    echo 20 | java fibonacci

Example of success

Source file

  // file
  int main ()
    int i = readInt() ; //5
    printInt(i) ;   //5
    printInt(i++) ; //5
    printInt(i) ;   //6
    printInt(++i) ; //7
    printInt(i) ;   //7

Running the compiler

    % lab3
    # produces good.class
    % echo 3 | java good.class

Compiling the code generator

The compiler is submitted as a source file package that can be compiled by typing make.

Test programs

Run your compiler and the generated code with the good files in the test suite before submitting the assignment. A script for running it can be found here - download the entire folder and compile it using make. The test script can then be run as in lab 2:

    ./progs-test-lab3 ../path/to/solution/

Success criteria

Your program must pass the test suite It is enough to run it on the "good" programs; the assumption is that the type checker has already in lab2 been able to reject the incorrect programs.

The solution must be written in an easily readable and maintainable way. In particular, tailoring it for the programs in the test suite is not maintainable!


Submit your lab by using Fire, when Lab 3 is in place.

If you have any problems getting the test program to run, or if you think that there is an error in the test suite, contact the teachers via the course Google group.