P5: Decaf ILOC Generator
Objective
The goal of our semester-long project is to gain experience in compiler implementation by constructing a simple compiler.
The goal of this part of the project is to gain experience implementing code generation by converting Decaf ASTs into a linear code (ILOC).
Introduction
The semester-long project for this course is to build a compiler for the Decaf language. In this project, you will implement code generation for Decaf, which will be the fourth phase in our compiler. You will do this by traversing the annotated AST from the fourth phase, generating equivalent ILOC code.
You should download the project starter files from the "Files" tab in Canvas. The starter files include many new .java files as well as .class files representing compiled solutions.
Before you begin writing code, you should spend some time reading through all of the infrastructure files provided in the starter files. Our compiler this semester is a large project. Your solution will need to interface with several other classes, and you will need to thoroughly read through those classes to understand their interactions. Also, there are utility functions that you may find useful.
If you have questions about the existing code, please ask them on the Piazza forum (see the link on the sidebar in Canvas).
For this project, you will be implementing MyILOCGenerator
, a
subclass of the ILOCGenerator
. These classes handle the conversion
from an annotated ASTProgram
to sequential ILOC code in an
ILOCProgram
structure.
To do this conversion, you will write visitor methods that generate code for
each AST node. I recommend doing this using the "code" and "reg" attributes to
store the generated code and any temporary result register, respectively, as we
discussed in class. I have provided many helper functions in
ILOCGenerator
to aid in writing these methods.
To help you test your code generation, I wrote a simple ILOC interpreter,
which you can find in the ILOCInterpreter
class. Its implementation
may be of interest to you as you write your code generator. You can also use the
interpreter to test your ILOC output, and I have added a final pass to
DecafCompiler
that invokes the interpreter on your generated ILOC
code.
It may also help to turn on tracing in the interpreter, which will print out
the system state after each instruction. To enable this, find the following
line in DecafCompiler
:
ILOCInterpreter interp = new ILOCInterpreter();
Change it to the following:
ILOCInterpreter interp = new ILOCInterpreter(true);
Assignment
WARNING: You should only proceed with actual development once you are SURE you understand exactly what your task is and how your code should interact with the rest of the system.
For this particular project, you should pay special attention to the following classes:
ILOCGenerator
- Base class for ILOC code generators.ILOCProgram
- Collection of ILOC functions.ILOCFunction
- Collection of ILOC instructions.ILOCInstruction
- Single ILOC instruction.ILOCOperand
- Single ILOC operand. This class also handles generation of temporary registers and anonymous labels.ILOCInterpreter
- Interprets ("executes") an ILOC program.AllocateSymbols
- AST traversal that calculates static coordinates and runtime locations for all symbols as well as the size of local variables for functions (necessary for prologue emission). This pass must be completed before code generation.
Implement the MyILOCGenerator
class. This project is by design
more open-ended than any of the previous projects in this course. There are
infinitely many ILOC programs that are equivalent to any given Decaf program.
Some are more efficient, some are easier to analyze, some are easier to read.
In addition, the reference compiler re-numbers registers and labels sequentially
in between P5 and P6. Thus, your generated output will likely not exactly match
the sample output below, and that is fine. I will primarily be testing your
emitted code for correctness. You must also abide by the standard calling
conventions as described in the language reference and as discussed in class.
Notes:
- You can ignore the PHI instruction--it's for data flow analysis in static single-assignment form, which we will not be doing in this project.
- You can also ignore the
ILOCBasicBlock
class--it's for building and analyzing control flow graphs, which we will not be using in this project. - Recursive functions will not work properly at this point in the project because we're re-using virtual registers across function invocations. We'll fix this in P6 by spilling registers at call sites so it's ok for now.
Sample Input
def int add(int x, int y) { return x + y; } def int main() { int a; a = 3; return add(a, 2); }
Sample Output
add: push bp // prologue i2i sp => bp addI sp, 0 => sp // allocate space for local variables (0 bytes) loadAI [bp+8] => r1 {x} loadAI [bp+12] => r2 {y} add r1, r2 => r3 i2i r3 => ret jump l1 // return (x+y) l1: i2i bp => sp // epilogue pop bp return main: push bp // prologue i2i sp => bp addI sp, -4 => sp // allocate space for local variables (4 bytes) loadI 3 => r4 storeAI r4 => [bp-4] {a} // a = 3 loadAI [bp-4] => r5 {a} loadI 2 => r6 push r6 push r5 call add addI sp, 8 => sp // de-allocate space for parameters (8 bytes) i2i ret => r7 i2i r7 => ret jump l2 // return add(a, 2) l2: i2i bp => sp // epilogue pop bp return Result: 5
Submission
Please submit your MyILOCGenerator.java
file
to the appropriate assignment on Canvas by the due date indicated there.
Code Reviews
One of the goals of this course is to encourage good software development practices, especially when building a large software system (such as a compiler). For this project, you will be assigned two other random students in the course. You must review their code and offer constructive feedback according to the given rubric.
Submit your review on Canvas by midnight a week following the original project due date.
Grading
Here is the grading breakdown for this project:
Automated tests | 80 |
Instructor review | 10 |
Peer review | 10 |
TOTAL | 100 |