Requirement
In this assignment, we will implement code generation for part of the language. The abstract syntax shown below has been modified to indicate which part of the language we need to implement now and how they map into JVM elements.1
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14Program ::= Name List<ParamDec> Block
class Name implements Runnable {
variables declared in List<ParamDec> are instance variables of the class
public Name(String[]args) {
initialize instance variables with values from args.
}
public static void main(String[] args) {
Name instance = new Name(args);
instance.run();
}
public void run() {
declarations and statements from block
}
}
The provided version of CodeGenVisitor.java also include a partially complete version of visitProgram. It is sufficient to generate code for an empty program. A test case in CodeGenVisitorTest with an empty program has been provided to illustrate how to put the pieces together, get useful output, etc. Use it to ensure that you have asm set up properly and as a starting point for your own tests. You will need asm and asm.util.
Because this fragment of our language does not have output, two routines, genPrint and genPrintTOS have been included with the provided version of CodeGenVisitor.java. These routines generate code to print a String and print the value on top of the stack (without consuming it), respectively. The CodeGenVisitor has a variable DEVEL and a variable GRADE that are set via parameters to the constructor. Both routines take a Boolean parameter that indicates whether these routines generate code or just to nothing. By adding these in appropriate places, you can easily generate code instrumented to show you what it is doing, and turn it off later.
In order to grade this assignment, we will be comparing the sequence of values written in assignment statements. (See assignment statement above.) Please follow directions exactly. This should be the ONLY call to genPrint of genPrintTOS that is passed the value of GRADE. You may insert calls with DEVEL anywhere you want. We will test with DEVEL = false and GRADE = true. The only output from the execution of your generated code should be these print statements.
It is difficult to write unit tests for these programs, nevertheless, Junit provides a convenient way to manage tests, even if they cannot easily automatically check the output. You should also be able to run your generated classfiles as a Java application program with the arguments on the command line.
Provided code
CodeGenVisitor.java starter code for code generation. visitProgram sets up the class and generates the main method and constructor, and the framework of the run method. You will need to make some changes, but it should compile and deal with the empty program as is. Implement all the methods marked “Implement this”.
CodeGenUtils.java some routines helpful during code generation
cop5556sp17.AST.Type.java A few useful modifications from the previous version.
Turn in
CodeGenVisitor.java, CodeGenVisitorTest.java, Parser.java, Scanner.java, SymbolTable.java, TypeCheckVisitor.java, all the classes in cop5555617.AST.
Troubleshooting Hints
If there are exceptions in the call to visitMaxs, you can temporarily replace1
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3cw=newClassWriter(ClassWriter.COMPUTE_FRAMES);
at the beginning of visitProgram with
cw=newClassWriter(0);
This will not yield a runnable class file, but it will allow you see the code that is being generated.
The JVM lecture also included some troubleshooting tips.