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Review of Static Program Analysis and Co/Contra-variance

Ras Bodik, Thibaud Hottelier, James IdeUC Berkeley

CS164: Introduction to Programming Languages and Compilers Fall 2010

Improve the course (we need your feedback)

Office hours with Pizzathis Wed, Nov 17, 5pm, in La Val’s

HKN surveys: Next Monday, Nov 22

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HW8: Static analysis (types and flow analysis)• Three problems, one for each lecture L18-

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• Preparation for the exam.

• Some reading

• Due in two weeks (Two days before exam)

• Today’s lecture and Thursday recitation will review the material 3

HW9: Final Project Design Document

Main goal: Flesh out HW7. Include details for implementation and evaluation.

What programs you want to write in your language?

– if you are building a tool, answer “What programs do you want to analyze with your debugger / …?”

– be specific, write down these programs

What implementation steps will you follow?– finish your design before you submit the

document– break down the implementation into ~6 steps– say what data structures and modules you’ll

implement

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Announcements

Contest 1: Fastest 164 Parserworkload: large files + many tiny files (onclick handlers)

Contest 2: Most Impressive 164 Browser Demo

goal: combine bQuery with Rx, potentially extending themsimplicity: future 164 students must be able to build it

Prizes: iPod nanos

Deadline: a few days after the second midterm

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Paid 164 Courseware Developer Job

Do you want to improve 164? Some of the tasks where we need your help:

Improve the browser, the language, the parser.

Rewrite the handouts with creative technical writing.

Develop homeworks that prepare for PAs (like HW4).

Talk to Ras if interested.

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Prolog program for Andersen algorithm

new(o1,x). % x=new_1 Foo()new(o2,z). % z=new_2 Bar()assign(x,y). % y=xassign(x,w). % w=xpf(z,y,f). % y.f=zgf(w,v,f). % v=w.f

flowsTo(O,X) :- new(O,X).flowsTo(O,X) :- assign(Y,X), flowsTo(O,Y).flowsTo(O,X) :- pf(Y,P,F), gf(R,X,F), aliasP,R),

flowsTo(O,Y).

alias(X,Y) :- flowsTo(O,X), flowsTo(O,Y).

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Computing pointsTo and alias relations

o2

y

z new

w

v

assign

x

o1

new

assign

pf[f]gf[f]

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Handling of method calls

Issue 1: Arguments and return values:– these are translated into assignments of the

form p=r

Example: Object foo(T x) { return x.f }r = new T; s = foo(r.g)

is translated intofoo_retval = foo_x.fr = new T; s = foo_retval; foo_x = r.g

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Imprecision in modeling of function calls

Example where our modeling leads to imprecision:

def id(x) { return x }a = id(new Foo())b = id(new Bar())

Let’s draw our inference graph:

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Handling of method calls

Issue 2: targets of virtual calls– call p.f() may call many possible methods – to do the translation shown on previous slide,

must determine what these targets are

Suggest two simple methods:–

–

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Nominal type systems: co/contra-variance

Assume:C extends B extends A.class B has method B foo(B).class C also has method foo.

Assume you are designing the type system for this language. What types of C’s foo should you allow?

B-->B, A-->A, C-->A, A-->C, …

How do we decide? Want some statements to be type safe. What does type safety mean?

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