In this assignment you shall experiment with and extend the material
from Chapter 2 of Nielson, Nielson and Hankin, mainly by
doing a selection of the exercises similar to those in the book.
The various parts are largely independent, and I have indicated when
you have the necessary information to complete the assignment.
The assignment may be done alone or, preferably, in pairs.
Every student should be able to explain orally and clearly
every part of the assignment he hands in. The lecturer has the freedom
to ask this explanation at any time, meaning that you might not be warned
Not all of the components below are worth the same number of grade point:
Part 1 to 3 are weighted at 20, 40, 40 percent.
The goal of the assignment
A large part of the chapter is devoted to developing a dataflow
analysis framework for an imperative language. To get a thorough
understanding of what is really happening underneath all that notation
you shall work on the following subjects:
- How to develop the transfer functions for a given analysis
- How chaotic iteration should be performed
- How to develop transfer functions for new language constructs and instantiate these for a specific analysis
Sometimes I ask you to give an illustrative, but small example.
The idea is that your example should be as varied and broad as possible,
but on the other hand should be as concise as possible. For instance,
in the case of Strongly Live Variables (see below), I expect an example
where a variable is strongly live, one which is not, one which is live
but not strongly live, and maybe you can think of other cases. The bottom line is that
your example is an alternative for a soundness proof, so the more convincing
your example, the more convinced people will be (actually, a proof also only
does the job when it is convincing).
The general rule is: Motivate your answers
The various parts of the assignment
Part 1: developing a new analysis within the framework
Do Exercise 2.4 for Strongly Live Variable Analysis
on page 136 of NNH, formulate your answer
similar to Table 2.4 on page 50.
Part 2: performing chaotic iteration
Design a While program of at least five blocks which well
illustrates the Strongly Live Variable Analysis (it should contain
at least one while loop).
Apply Chaotic Iteration to the set of equations that you obtain as a result of applying
Part 1 to your program, showing also intermediate
values for the iterations (similar to what I do in the slides for
Available Expressions). Indicate how SLV is different for this example
from the standard LV (and make sure that your example allows you to
illustrate this fact).
Part 3: adding new constructs to the While language
Add the following three programming constructs to the While
language. Describe, in general, what has to change to accommodate
each of the constructs. To avoid too much work: you don't have to give the semantics
of the new language constructs, but it is wise to describe it for me.
(Hint: sometimes it is sufficient to add new transfer functions, sometimes
a change has to be made to a different parameter of the monotone framework.
Deciding this is, of course, up to you.)
print a statement where
a is an arithmetic
expression. Show how to adapt the Strongly Live Analysis to accommodate
programs which contain
print statements. Devise a small
program which shows that your extension works as expected. (You do not
need to perform Chaotic Iteration. What you should do is give the
equations for your program, propose a good (preferably the best)
solution, indicate why you think this is a reasonable solution
and verify that it fulfills the equations).
- Simultaneous assignments: a simultaneous assignment is of the form
v1, ..., vn := a1, ..., an, which assigns the value of
v2 and so on. The semantics of such a statement is that first
the sequence of expressions
is evaluated, and when this is done, the resulting values are stored
in the corresponding variables in left to right order.
Add simultaneous assignments to the While language and show how
to adapt the Strongly Live Variable Analysis to accomodate it.
Illustrate that your solution works by giving an example.
- The break and continue statement: the semantics of break is to leave the enclosing
loop statement, the semantics of continue is to proceed to the enclosing loop condition.
What break and continue do when they are outside any loop, I leave up to you. But you have to make up your mind for each what happens
and document that well.
For testing, devise a small, but suitably complicated program and analyze it to illustrate that your proposed modifications work
for Available Expressions Analysis described in the book.
What, how and when to submit
Details can be found here
In whatever fashion you hand things in make sure things are clear and
readable and on time. Make sure that you motivate
Experiences from last year
This is a start-up assignment and generally not very difficult.
- 14 Nov 2008