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Flow insensitive pointer analysis: fixed S1: l := new Cons p := l S2: t := new Cons *p := t p := t l p S1 l p tS2 l p S1 t S2 l t S1 p S2 l t S1 p S2 l t S1 p L2 l t S1 p S2 l t S1 p S2 l t S1 p S2 l t L1 p L2 l t S1 p S2 Iter 1Iter 2Iter 3 l t S1 p S2 Final result This is Andersen’s algorithm ’94

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Flow insensitive loss of precision S1: l := new Cons p := l S2: t := new Cons *p := t p := t l t S1 p S2 l t S1 p S2 l t S1 p S2 l t S1 p S2 Flow-sensitive SolnFlow-insensitive Soln l t S1 p S2

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Flow insensitive loss of precision Flow insensitive analysis leads to loss of precision! main() { x := &y;... x := &z; } Flow insensitive analysis tells us that x may point to z here! However: –uses less memory (memory can be a big bottleneck to running on large programs) –runs faster

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Worst case complexity of Andersen *x = y x abc y def x abc y def Worst case: N 2 per statement, so at least N 3 for the whole program. Andersen is in fact O(N 3 )

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New idea: one successor per node Make each node have only one successor. This is an invariant that we want to maintain. x a,b,c y d,e,f *x = y x a,b,c y d,e,f

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x *x = y y More general case for *x = y

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x *x = y yxyxy More general case for *x = y

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x x = *y y Handling: x = *y

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x x = *y yxyxy Handling: x = *y

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x x = y y x = &y xy Handling: x = y (what about y = x?) Handling: x = &y

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x x = y yxyxy x = &y xyx y,… xy Handling: x = y (what about y = x?) Handling: x = &y get the same for y = x

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Our favorite example, once more! S1: l := new Cons p := l S2: t := new Cons *p := t p := t 1 2 3 4 5

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Our favorite example, once more! S1: l := new Cons p := l S2: t := new Cons *p := t p := t l S1 t S2 p l S1 l p l t S2 p l S1,S2 tp 1 2 3 4 5 12 3 l S1 t S2 p 4 5

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Flow insensitive loss of precision S1: l := new Cons p := l S2: t := new Cons *p := t p := t l t S1 p S2 l t S1 p S2 l t S1 p S2 l t S1 p S2 Flow-sensitive Subset-based Flow-insensitive Subset-based l t S1 p S2 l S1,S2 tp Flow-insensitive Unification- based

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bar() { i := &a; j := &b; foo(&i); foo(&j); // i pnts to what? *i :=...; } void foo(int* p) { printf(“%d”,*p); } 1 2 3 4 Another example

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bar() { i := &a; j := &b; foo(&i); foo(&j); // i pnts to what? *i :=...; } void foo(int* p) { printf(“%d”,*p); } i a j b p i a i a j b i a j b p i,j a,b p 1 2 3 4 12 Another example 4 3

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Advanced Pointer Analysis Combine flow-sensitive/flow-insensitive Clever data-structure design Context-sensitivity

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Summary of material Dataflow Analysis Program Representations Interprocedural Analysis Points-to Analysis

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Research at UCSD Compiler Correctness Race detection Refactoring Javascript Energy

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U NIVERSITY OF M ASSACHUSETTS, A MHERST Department of Computer Science Emery Berger University of Massachusetts, Amherst Advanced Compilers CMPSCI 710.

U NIVERSITY OF M ASSACHUSETTS, A MHERST Department of Computer Science Emery Berger University of Massachusetts, Amherst Advanced Compilers CMPSCI 710.

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