Project 9: Compilation

In this project, you will complete a compiler for SwiJay (called JaySea, inspired by javac) which produces Java VM assembly (which can then be used to generate classfiles).

You should mainly think of this as a compiler for Jay, except that one extra tricky part--switch statements---is added at the end.

1. Set-up.

Many other pieces are provided for you, and can be found in a tar file.

cp ~tvandrun/Public/cs365/proj9.tar .

The system works like this. The script jaysea feeds a Jay program into the ML-written compiler, which produces a file in Java bytecode assembly (actually a Jasmin input file). For example,

./jaysea Euclid.swijay

will produce Euclid.jj. Then the Java assembler Jasmin can be used to produce the classfile. For example,

jasmin Euclid.jj

will produce Euclid.class. Now

java Euclid

will run the program.

2. Your task

Your task is finishing the compilation functions in compile.sml. For all Jay statements and expressions, what series of instructions needs to be emitted, and how does that affect the stack?

Some specifics:

• The only changes to the code you'll need to do are to finish the compileStmt() and compileExpr() functions (and add any helper functions you deep necessary).
• As examples, I have already implemented certain parts of compileStmt() (skip, block, and loop) and compileExpr() (binary expression). Currently those functions will emit no code for the other kinds of expressions.
• You can looks things up in the symbol table using get(). This will return an integer (a local variable number) for a given identifier (a local variable name).
• Remember that the emit() function takes a string and an integer; the integer is the effect that the instruction has on the stack. This keeps track of stack depth consistency and the maximum stack depth.
• In theory, we could print out booleans as booleans, not as ints. However, that would require type checking, which I never did for SwiJay. So, for simplicity's sake, you may print out all values--integer or boolean--as ints.

3. Suggestions

Make use of these resources:

• The Jasmin Home Page, especially the description of instructions.
• The Java VM Spec, especially the VM instruction set (Notice the alphabetical indices at the top of the page.)

Make your changes to JaySea incrementally. First implement prints and int literals, and then compile a program that just prints an int literal and make sure it works. Then gradually add other statements and expressions.

Do switch statements last. Switch statements can be compiled to the instruction lookupswitch (or, if you're really ambitious, tableswitch). Remember that the statements inside a switch are called InSwitchStatements. In my version, I wrote a helper function called compileInSwitchStmt(), analogous to compileStmt().

As you work, I recommend you have both Jay and Java versions of your test files. Compile the Java versions and disassemble them with javap to see what the result might look like. Your output does not have to be identical to what javac produces--often there is an equivalent series of instructions that you'll find are easier to produce---but javac can guide you through some of the knottier statements.

4. Extra credit

All you need is a compiler that produces programs that work to get full credit. But there are some optimizations you could perform for which I will award extra credit. For example, if (x > 0)... would naively be complied by loading x, pushing 0, generating the sequence for >, and then ifne, but a more efficient version would load x and use if_icmpgt. Also, x = x + 1; could be done using the iinc instruction. Some switch statements can be compiled to a tableswitch instead of a lookupswitch.

5. To turn in

To turn in this project, please copy your compile.sml and, if you did any optimizations for extra credit, a text file describing what you did to the turn-in directory I will prepare for you:

/cslab/class/cs365/turnin/proj9/xxxxx

where "xxxxx" is [lily|chet|christopher|tim|david|ben|caleb]

Due: Wed, April 28, 5:00 pm UTC-12. For those of you who have not used up your late days, Fri, April 30 (the last day of classes) at 5:00 pm is the absolute deadline for this project, meaning that even if you still have all three of your late days left, you may apply no more than two late days to this project.