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Points-to Analysis in Almost Linear Time

Points-to Analysis in Almost Linear Time. paper by Bjarne Steensgaard 23rd ACM Symposium on Principles of Programming Languages (POPL'96) Microsoft Research Technical Report MSR-TR-95-08. presented by Jeff Blank CMSC 858Z Spring 2004. Outline of Talk. Background Source Language

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Points-to Analysis in Almost Linear Time

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  1. Points-to Analysis in Almost Linear Time paper by Bjarne Steensgaard 23rd ACM Symposium on Principles of Programming Languages (POPL'96) Microsoft Research Technical Report MSR-TR-95-08 presented by Jeff Blank CMSC 858Z Spring 2004

  2. Outline of Talk • Background • Source Language • Type System • Inference Algorithm • Examples

  3. Motivation • Why this paper? • and which paper, exactly? • What type of analysis? • flow-insensitive, context-insensitive, interprocedural

  4. Example: Factorial Source Language fact = fun(x)->(r) if lessthan(x 1) then r = 1 else xminusone = subtract(x 1) nextfac = fact(xminusone) r = multiply(x nextfac) fi result = fact(10) S ::= x = y | x = &y | x = *y | x = op(y1. . .yn) | x = allocate(y) | *x = y | x = fun(f1…fn)->(r1…rm) S* | x1…xm= p(y1…yn)

  5. Non-standard types  ::=  x   ::=  | ref()  ::=  | lam(1…n)(n+1…n+m)

  6. Typing Rules • “obvious” vs. with partial order • (review on sheet) _ = whatever!

  7. Type Inference System • imposing the rules = performing points-to analysis • Algorithm: • Initialization • assumptions • all variables set to different types • Inference • impose the rules, i.e. merge types as necessary • one pass

  8. a x,z b p y c Example Run a = &x b = &y if p then y = &z; else y = &x fi c = &y

  9. m i j n More Examplesoriginal algorithm m = 42 i = m j = m j = &n

  10. m i j n More Examplesimproved algorithm m = 42 i = m j = m j = &n

  11. m i j n More Examplesimproved algorithm (joining with pending set) m = 42 i = m j = m m = &n

  12. Efficiency of system • O(N(N,N)) •  is inverse Ackermann’s function, cost of find • Compared to others...

  13. Other comments • no support for separate types in a composite object (e.g. a struct) • is fast • even on mid-nineties computers • test data (show graph)

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