ECS 142 Compilers Handout 8
Extra Credit Programming Assignment
Due Saturday, March 19, 2005 at 11:59pm
1 Introduction
This extra credit programming assignment is intended to be a fun project with which to end the semester.
You will need to implement some optimizations in your compiler such that the generated code has the
same semantic meaning, but executes in fewer cycles.
You may work in a group of one or two people. The submit program will ask you to specify group
members when you turn in your assignment.
2 Optimizer Project
Extra credit will be awarded for projects that, in addition to code generation, perform some significant
optimization of the code. The amount of extra credit depends on how well the optimization is written,
documented, and demonstrated. Two critical factors are
1. correctness (the optimizations don’t result in incorrect programs); and
2. the percentage speed-up your optimized code achieves over coolc, as measured by a weighted
sum of the instructions executed on spim over a suite of benchmarks of our choosing.
To find out how many instructions a Cool program executes, run spim with the -keepstats option.
There are many possible optimizations to implement; see the ASU chapters 9 and 10 for ideas.
Assuming your initial code generator is straightforward (like coolc’s), then two directions that may yield
significant improvement are (1) improving register usage and (2) specializing the implementation of the
basic classes Int and String.
We have not implemented an optimization phase in coolc, so we have no skeleton code to give you—
you are on your own. If you want to do an optimization phase, you are encouraged to talk it over with
one of the course staff first. Under absolutely no circumstances should you try optimization before your
code generator is finished!!
There is a -O flag that controls the global variable cgen optimize (C++) and Flags.cgen optimize
(Java). You may use this flag to switch between generating normal code and optimized code. For this
project, we will always run your compiler with the -O flag on.
The total extra credit for doing optimization will not exceed 5% of the total grade for the course.
Roughly speaking, the extra credit is worth up to about one-third of one of the two large programming
assignments.
3 Grading
The final curve for the course will be determined before including the extra credit. In other words, if you
elect not to do extra credit work, you will not be at a disadvantage in the final grading with respect to
those who do.
This extra-credit option is open-ended; you can do as much as you like. We will award credit for
results. For example, a project that merely attempts, but does not complete, an optimization phase may
receive as little as no extra credit.
Winter 2005 page 1 of 2
