Fast PolyhedraAbstract Domainelina.ethz.ch/slides/popl2017-fast-polyhedra.pdf · Polyhedra Domain Analysis Automatic Discovery of Linear Restraints Among Variables of a Program, POPL’78

Gagandeep Singh Markus Püschel Martin Vechev

Department of Computer Science

ETH Zurich

Fast Polyhedra Abstract Domain

Polyhedra Domain AnalysisAutomatic Discovery of Linear Restraints Among Variables of a Program, POPL’78


Introduced by Patrick Cousot and Nicolas Halbwachs

Represents linear constraints between program variables

Patrick Cousot Nicolas Halbwachs


Introduced by Patrick Cousot and Nicolas Halbwachs

Represents linear constraints between program variables

y ≤ 3

-x ≤

2

Patrick Cousot Nicolas Halbwachs

Polyhedra Domain Analysis


if(*){

y:=2x-1;

}

else{

y:=2x-2;

}

assert(y<=2x);


if(*){

y:=2x-1;

}

else{

y:=2x-2;

}

Abstract

Domain

Can Prove the

Assertion?

Interval ❌

Pentagon ❌

Zones ❌

Octagon ❌

Polyhedra ✅assert(y<=2x);


if(*){

y:=2x-1;

}

else{

y:=2x-2;

}

Abstract

Domain

Can Prove the

Assertion?

Interval ❌

Pentagon ❌

Zones ❌

Octagon ❌

Polyhedra ✅assert(y<=2x);

Polyhedra analysis: time and space exponential in number of variables

This work: contributions


Online decomposition: reduction in space and time without losing precision



Constant factor improvements via reduced operation count and cache optimizations




elina.ethz.ch

Complete end-to-end

implementation

http://elina.ethz.ch/




elina.ethz.ch

Complete end-to-end

implementation

Driver NewPolka PPL ELINA

500 var

39K LOC

OOM

(> 12 GB)

OOM

(> 12 GB)

4 sec

0.9 GB

650 var

25K LOC

TO

(> 4 hr)

TO

(> 4 hr)

2 sec

0.4 GB


Double Representation of Polyhedron

x1

x2 = 2

x2

𝒞 = {-x2 ≤ -2, x2 ≤ 2x1}

m: number of constraints

Constraints(⊔) easy

with the Generators


x1

x2 = 2

x2

𝒞 = {-x2 ≤ -2, x2 ≤ 2x1}

m: number of constraints

x1

x2

Vertices 𝒱 = {(1,2)},

Rays ℛ = {(1,2), (1,0)},

Lines 𝒵 = ∅g: number of generators

(1,2) (1,0)

Generators (⊔) easy

with the GeneratorsConstraints(⊔) easy

with the Generators


Asymptotic Time Complexity of Polyhedra


Operator Constraints Generators Both

Join (⊔) exp(n,m) Ο(𝑛𝑔) Ο(𝑛𝑔)

Meet (⊓) Ο(𝑛𝑚) exp(n,g) Ο(𝑛𝑚)

Inclusion (⊑) exp(n,m) exp(n,g) Ο(𝑛𝑔𝑚)

Assignment Ο(𝑛𝑚2) Ο(𝑛𝑔) Ο(𝑛𝑔)

Conditional Ο(𝑛) exp(n,g) Ο(𝑛)


Operator Constraints Generators Both

Join (⊔) exp(n,m) Ο(𝑛𝑔) Ο(𝑛𝑔)

Meet (⊓) Ο(𝑛𝑚) exp(n,g) Ο(𝑛𝑚)

Inclusion (⊑) exp(n,m) exp(n,g) Ο(𝑛𝑔𝑚)

Assignment Ο(𝑛𝑚2) Ο(𝑛𝑔) Ο(𝑛𝑔)

Conditional Ο(𝑛) exp(n,g) Ο(𝑛)

Constraints Generators

exp(n,m)

exp(n,g)

Key Idea: Online Decomposition


{𝒙𝟏 ≤ 𝟐𝒙𝟐,

𝒙𝟐 = 𝟐,𝒙𝟏 + 𝒙𝟐 + 𝟐𝒙𝟑 ≤ 𝟓,

𝒙𝟒 - 𝒙𝟓 ≤ 𝟑,

𝒙𝟓 = 𝟏,

𝒙𝟔 = 𝟐}

Polyhedron


{𝒙𝟏 ≤ 𝟐𝒙𝟐,

𝒙𝟐 = 𝟐,𝒙𝟏 + 𝒙𝟐 + 𝟐𝒙𝟑 ≤ 𝟓,

𝒙𝟒 - 𝒙𝟓 ≤ 𝟑,

𝒙𝟓 = 𝟏,

𝒙𝟔 = 𝟐}

Polyhedron {𝒙𝟏 ≤ 𝟐𝒙𝟐,

𝒙𝟐 = 𝟐,𝒙𝟏 + 𝒙𝟐 + 𝟐𝒙𝟑 ≤ 𝟓}

{𝒙𝟒 - 𝒙𝟓 ≤ 𝟑,

𝒙𝟓 = 𝟏}

{𝒙𝟔 = 𝟐}

Set of factors


{𝒙𝟏 ≤ 𝟐𝒙𝟐,

𝒙𝟐 = 𝟐,𝒙𝟏 + 𝒙𝟐 + 𝟐𝒙𝟑 ≤ 𝟓,

𝒙𝟒 - 𝒙𝟓 ≤ 𝟑,

𝒙𝟓 = 𝟏,

𝒙𝟔 = 𝟐}


𝒙𝟐 = 𝟐,𝒙𝟏 + 𝒙𝟐 + 𝟐𝒙𝟑 ≤ 𝟓}

{𝒙𝟒 - 𝒙𝟓 ≤ 𝟑,

𝒙𝟓 = 𝟏}

{𝒙𝟔 = 𝟐}

Set of factors

Partition (𝜋) =

set of blocks

{𝒙𝟏, 𝒙𝟐, 𝒙𝟑}

{𝒙𝟒, 𝒙𝟓}

{𝒙𝟔}


working on smaller Polyhedra enables reduction in space and time

{𝒙𝟏 ≤ 𝟐𝒙𝟐,

𝒙𝟐 = 𝟐,𝒙𝟏 + 𝒙𝟐 + 𝟐𝒙𝟑 ≤ 𝟓,

𝒙𝟒 - 𝒙𝟓 ≤ 𝟑,

𝒙𝟓 = 𝟏,

𝒙𝟔 = 𝟐}


𝒙𝟐 = 𝟐,𝒙𝟏 + 𝒙𝟐 + 𝟐𝒙𝟑 ≤ 𝟓}

{𝒙𝟒 - 𝒙𝟓 ≤ 𝟑,

𝒙𝟓 = 𝟏}

{𝒙𝟔 = 𝟐}

Set of factors

Partition (𝜋) =

set of blocks

{𝒙𝟏, 𝒙𝟐, 𝒙𝟑}

{𝒙𝟒, 𝒙𝟓}

{𝒙𝟔}

Permissible Partitions


{𝒙𝟏 ≤ 𝟐𝒙𝟐,

𝒙𝟐 = 𝟐,𝒙𝟏 + 𝒙𝟐 + 𝟐𝒙𝟑 ≤ 𝟓,

𝒙𝟒 - 𝒙𝟓 ≤ 𝟑,

𝒙𝟓 = 𝟏,

𝒙𝟔 = 𝟐}

Polyhedron


{𝒙𝟏 ≤ 𝟐𝒙𝟐,

𝒙𝟐 = 𝟐,𝒙𝟏 + 𝒙𝟐 + 𝟐𝒙𝟑 ≤ 𝟓,

𝒙𝟒 - 𝒙𝟓 ≤ 𝟑,

𝒙𝟓 = 𝟏,

𝒙𝟔 = 𝟐}

PolyhedronBest (finest)

partition (𝜋)

{𝒙𝟏, 𝒙𝟐, 𝒙𝟑}

{𝒙𝟒, 𝒙𝟓}

{𝒙𝟔}


{𝒙𝟏 ≤ 𝟐𝒙𝟐,

𝒙𝟐 = 𝟐,𝒙𝟏 + 𝒙𝟐 + 𝟐𝒙𝟑 ≤ 𝟓,

𝒙𝟒 - 𝒙𝟓 ≤ 𝟑,

𝒙𝟓 = 𝟏,

𝒙𝟔 = 𝟐}


partition (𝜋)

{𝒙𝟏, 𝒙𝟐, 𝒙𝟑}

{𝒙𝟒, 𝒙𝟓}

{𝒙𝟔}

{𝒙𝟏, 𝒙𝟐, 𝒙𝟑}

{𝒙𝟒, 𝒙𝟓, 𝒙𝟔}

Permissible

partition (𝜋)


{𝒙𝟏 ≤ 𝟐𝒙𝟐,

𝒙𝟐 = 𝟐,𝒙𝟏 + 𝒙𝟐 + 𝟐𝒙𝟑 ≤ 𝟓,

𝒙𝟒 - 𝒙𝟓 ≤ 𝟑,

𝒙𝟓 = 𝟏,

𝒙𝟔 = 𝟐}


partition (𝜋)

{𝒙𝟏, 𝒙𝟐, 𝒙𝟑}

{𝒙𝟒, 𝒙𝟓}

{𝒙𝟔}

{𝒙𝟏, 𝒙𝟐, 𝒙𝟑}

{𝒙𝟒, 𝒙𝟓, 𝒙𝟔}

Permissible

partition (𝜋)

Invalid

partition

{𝒙𝟏, 𝒙𝟐}

{𝒙𝟑, 𝒙𝟒, 𝒙𝟓}

{𝒙𝟔}


Definition: A partition 𝜋 is permissible for Polyhedron P, if there are no two variables 𝒙𝒊 and 𝒙𝒋 in different blocks of 𝜋 related by a constraint in P

{𝒙𝟏 ≤ 𝟐𝒙𝟐,

𝒙𝟐 = 𝟐,𝒙𝟏 + 𝒙𝟐 + 𝟐𝒙𝟑 ≤ 𝟓,

𝒙𝟒 - 𝒙𝟓 ≤ 𝟑,

𝒙𝟓 = 𝟏,

𝒙𝟔 = 𝟐}


partition (𝜋)

{𝒙𝟏, 𝒙𝟐, 𝒙𝟑}

{𝒙𝟒, 𝒙𝟓}

{𝒙𝟔}

{𝒙𝟏, 𝒙𝟐, 𝒙𝟑}

{𝒙𝟒, 𝒙𝟓, 𝒙𝟔}

Permissible

partition (𝜋)

Invalid

partition

{𝒙𝟏, 𝒙𝟐}

{𝒙𝟑, 𝒙𝟒, 𝒙𝟓}

{𝒙𝟔}

Partition of Variable Set: Summary


The set of all partitions of variable set 𝒳 form a lattice ordered by “finer than” (<) relation

The best (finest) partition 𝜋𝑃 for Polyhedron P is unique

Any 𝜋, s.t., 𝜋𝑃 < 𝜋, is permissible

An unconstrained variable 𝑥𝑖 yields a singleton set {𝑥𝑖} in the partition


The set of all partitions of variable set 𝒳 form a lattice ordered by “finer than” (<) relation

The best (finest) partition 𝜋𝑃 for Polyhedron P is unique

Any 𝜋, s.t., 𝜋𝑃 < 𝜋, is permissible

An unconstrained variable 𝑥𝑖 yields a singleton set {𝑥𝑖} in the partition

Challenge: maintain permissible partitions for > 30 operators

Operator: Conditional


Definition: Let 𝜋 be a partition and ℬ be a block, then 𝜋 ↑ ℬ is the finest partition 𝜋’ such that 𝜋 ⊑ 𝜋’ and ℬ is a subset of an element of 𝜋’

Theorem (finest partition after conditional):

If O ≠⊥ and let ℬ be block containing all variables appearing in the conditional,then 𝜋𝑂 = 𝜋𝑃 ↑ ℬ





{𝒙𝟏 ≤ 𝟐𝒙𝟐,

𝒙𝟐 = 𝟐,𝒙𝟏 + 𝒙𝟐 + 𝟐𝒙𝟑 ≤ 𝟓}

{𝒙𝟒 - 𝒙𝟓 ≤ 𝟑,

𝒙𝟓 = 𝟏}

{𝒙𝟔 = 𝟐}

P 𝜋𝑃

{𝒙𝟏, 𝒙𝟐, 𝒙𝟑}

{𝒙𝟒, 𝒙𝟓}

{𝒙𝟔}





{𝒙𝟏 ≤ 𝟐𝒙𝟐,

𝒙𝟐 = 𝟐,𝒙𝟏 + 𝒙𝟐 + 𝟐𝒙𝟑 ≤ 𝟓}

{𝒙𝟒 - 𝒙𝟓 ≤ 𝟑,

𝒙𝟓 = 𝟏}

{𝒙𝟔 = 𝟐}

P 𝜋𝑃

{𝒙𝟏, 𝒙𝟐, 𝒙𝟑}

{𝒙𝟒, 𝒙𝟓}

{𝒙𝟔}

if( 𝒙𝟐 ≤ 𝟐𝒙𝟒)





{𝒙𝟏 ≤ 𝟐𝒙𝟐,

𝒙𝟐 = 𝟐,𝒙𝟏 + 𝒙𝟐 + 𝟐𝒙𝟑 ≤ 𝟓}

{𝒙𝟒 - 𝒙𝟓 ≤ 𝟑,

𝒙𝟓 = 𝟏}

{𝒙𝟔 = 𝟐}

P 𝜋𝑃

{𝒙𝟏, 𝒙𝟐, 𝒙𝟑}

{𝒙𝟒, 𝒙𝟓}

{𝒙𝟔}

O 𝜋𝑂{𝒙𝟏 ≤ 𝟐𝒙𝟐,

𝒙𝟐 = 𝟐,𝒙𝟏 + 𝒙𝟐 + 𝟐𝒙𝟑 ≤ 𝟓,

𝒙𝟒 - 𝒙𝟓 ≤ 𝟑,

𝒙𝟓 = 𝟏,

𝒙𝟐 ≤ 𝟐𝒙𝟒}

{𝒙𝟔 = 𝟐} {𝒙𝟔}

{𝒙𝟏, 𝒙𝟐, 𝒙𝟑,

𝒙𝟒, 𝒙𝟓}if( 𝒙𝟐 ≤ 𝟐𝒙𝟒)





{𝒙𝟏 ≤ 𝟐𝒙𝟐,

𝒙𝟐 = 𝟐,𝒙𝟏 + 𝒙𝟐 + 𝟐𝒙𝟑 ≤ 𝟓}

{𝒙𝟒 - 𝒙𝟓 ≤ 𝟑,

𝒙𝟓 = 𝟏}

{𝒙𝟔 = 𝟐}

P 𝜋𝑃

{𝒙𝟏, 𝒙𝟐, 𝒙𝟑}

{𝒙𝟒, 𝒙𝟓}

{𝒙𝟔}

O 𝜋𝑂{𝒙𝟏 ≤ 𝟐𝒙𝟐,

𝒙𝟐 = 𝟐,𝒙𝟏 + 𝒙𝟐 + 𝟐𝒙𝟑 ≤ 𝟓,

𝒙𝟒 - 𝒙𝟓 ≤ 𝟑,

𝒙𝟓 = 𝟏,

𝒙𝟐 ≤ 𝟐𝒙𝟒}

{𝒙𝟔 = 𝟐} {𝒙𝟔}

{𝒙𝟏, 𝒙𝟐, 𝒙𝟑,

𝒙𝟒, 𝒙𝟓}if( 𝒙𝟐 ≤ 𝟐𝒙𝟒)

𝓑 = {𝒙𝟐, 𝒙𝟒}

Operator: Assignment


{𝒙𝟏 ≤ 𝟐𝒙𝟐,

𝒙𝟐 = 𝟐,𝒙𝟏 + 𝒙𝟐 + 𝟐𝒙𝟑 ≤ 𝟓}

{𝒙𝟒 - 𝒙𝟓 ≤ 𝟑,

𝒙𝟓 = 𝟏}

{𝒙𝟔 = 𝟐}

P 𝜋𝑃

{𝒙𝟏, 𝒙𝟐, 𝒙𝟑}

{𝒙𝟒, 𝒙𝟓}

{𝒙𝟔}


{𝒙𝟏 ≤ 𝟐𝒙𝟐,

𝒙𝟐 = 𝟐,𝒙𝟏 + 𝒙𝟐 + 𝟐𝒙𝟑 ≤ 𝟓}

{𝒙𝟒 - 𝒙𝟓 ≤ 𝟑,

𝒙𝟓 = 𝟏}

{𝒙𝟔 = 𝟐}

P 𝜋𝑃

{𝒙𝟏, 𝒙𝟐, 𝒙𝟑}

{𝒙𝟒, 𝒙𝟓}

{𝒙𝟔}

𝒙𝟐∶= 𝟐𝒙𝟒


{𝒙𝟏 ≤ 𝟐𝒙𝟐,

𝒙𝟐 = 𝟐,𝒙𝟏 + 𝒙𝟐 + 𝟐𝒙𝟑 ≤ 𝟓}

{𝒙𝟒 - 𝒙𝟓 ≤ 𝟑,

𝒙𝟓 = 𝟏}

{𝒙𝟔 = 𝟐}

P 𝜋𝑃

{𝒙𝟏, 𝒙𝟐, 𝒙𝟑}

{𝒙𝟒, 𝒙𝟓}

{𝒙𝟔}

O 𝜋𝑂

{𝒙𝟏 ≤ 𝟒,

𝒙𝟏 + 𝟐𝒙𝟑 ≤ 𝟑,

{𝒙𝟔 = 𝟐} {𝒙𝟔}

{𝒙𝟏, 𝒙𝟑}

𝒙𝟐∶= 𝟐𝒙𝟒{𝒙𝟒 - 𝒙𝟓 ≤ 𝟑,

𝒙𝟓 = 𝟏,

𝒙𝟐= 𝟐𝒙𝟒}

{𝒙𝟐, 𝒙𝟒, 𝒙𝟓}


Theorem (finest partition after assignment):

Let ℬ be block containing all variables appearing for assignment 𝒙𝒊 ≔ 𝒆 , and let 𝜋𝒊 = {𝒳 ∖{𝒙𝒊}, {𝒙𝒊}}, then 𝜋𝑂 = (𝜋𝑃 ⊓ 𝜋𝒊) ↑ ℬ

{𝒙𝟏 ≤ 𝟐𝒙𝟐,

𝒙𝟐 = 𝟐,𝒙𝟏 + 𝒙𝟐 + 𝟐𝒙𝟑 ≤ 𝟓}

{𝒙𝟒 - 𝒙𝟓 ≤ 𝟑,

𝒙𝟓 = 𝟏}

{𝒙𝟔 = 𝟐}

P 𝜋𝑃

{𝒙𝟏, 𝒙𝟐, 𝒙𝟑}

{𝒙𝟒, 𝒙𝟓}

{𝒙𝟔}

O 𝜋𝑂

{𝒙𝟏 ≤ 𝟒,

𝒙𝟏 + 𝟐𝒙𝟑 ≤ 𝟑,

{𝒙𝟔 = 𝟐} {𝒙𝟔}

{𝒙𝟏, 𝒙𝟑}

𝒙𝟐∶= 𝟐𝒙𝟒{𝒙𝟒 - 𝒙𝟓 ≤ 𝟑,

𝒙𝟓 = 𝟏,

𝒙𝟐= 𝟐𝒙𝟒}

{𝒙𝟐, 𝒙𝟒, 𝒙𝟓}


Theorem (finest partition after assignment):

Let ℬ be block containing all variables appearing for assignment 𝒙𝒊 ≔ 𝒆 , and let 𝜋𝒊 = {𝒳 ∖{𝒙𝒊}, {𝒙𝒊}}, then 𝜋𝑂 = (𝜋𝑃 ⊓ 𝜋𝒊) ↑ ℬ

{𝒙𝟏 ≤ 𝟐𝒙𝟐,

𝒙𝟐 = 𝟐,𝒙𝟏 + 𝒙𝟐 + 𝟐𝒙𝟑 ≤ 𝟓}

{𝒙𝟒 - 𝒙𝟓 ≤ 𝟑,

𝒙𝟓 = 𝟏}

{𝒙𝟔 = 𝟐}

P 𝜋𝑃

{𝒙𝟏, 𝒙𝟐, 𝒙𝟑}

{𝒙𝟒, 𝒙𝟓}

{𝒙𝟔}

O 𝜋𝑂

{𝒙𝟏 ≤ 𝟒,

𝒙𝟏 + 𝟐𝒙𝟑 ≤ 𝟑,

{𝒙𝟔 = 𝟐} {𝒙𝟔}

{𝒙𝟏, 𝒙𝟑}

𝒙𝟐∶= 𝟐𝒙𝟒{𝒙𝟒 - 𝒙𝟓 ≤ 𝟑,

𝒙𝟓 = 𝟏,

𝒙𝟐= 𝟐𝒙𝟒}

{𝒙𝟐, 𝒙𝟒, 𝒙𝟓}𝓑 = {𝒙𝟐, 𝒙𝟒}

Lattice Operators

Lattice Operators

Theorem (finest partition for ⊑):

If 𝑃 ⊑ 𝑄 and 𝑃 ≠⊥, then 𝜋𝑄 ⊑ 𝜋𝑃

Theorem: (finest partition after ⊓):

If 𝑃 ⊓ 𝑄 ≠⊥ , then 𝜋𝑂 = 𝜋𝑃 ⊔ 𝜋𝑄

For join (⊔), no general relationship exists between 𝜋𝑂, 𝜋𝑃 and 𝜋𝑄

Operator: Join (⊔)


{𝒙𝟏 − 𝒙𝟐 ≤ 𝟎,

𝒙𝟏 ≤ 𝟎}

{𝒙𝟑 = 𝟏}

P 𝜋𝑃

{𝒙𝟏, 𝒙𝟐}

{𝒙𝟑}


{𝒙𝟏 − 𝒙𝟐 ≤ 𝟎,

𝒙𝟏 ≤ 𝟎}

{𝒙𝟑 = 𝟏}

P 𝜋𝑃

{𝒙𝟏, 𝒙𝟐}

{𝒙𝟑}

⊔


{𝒙𝟏 − 𝒙𝟐 ≤ 𝟎,

𝒙𝟏 ≤ 𝟎}

{𝒙𝟑 = 𝟏}

P 𝜋𝑃

{𝒙𝟏, 𝒙𝟐}

{𝒙𝟑}

{𝒙𝟏 ≤ 𝟐}

{𝒙𝟑 = 𝟎}

Q 𝜋𝑄

{𝒙𝟏}

{𝒙𝟑}

⊔ ∅ {𝒙𝟐}


{𝒙𝟏 − 𝒙𝟐 ≤ 𝟎,

𝒙𝟏 ≤ 𝟎}

{𝒙𝟑 = 𝟏}

P 𝜋𝑃

{𝒙𝟏, 𝒙𝟐}

{𝒙𝟑}

{𝒙𝟏 ≤ 𝟐}

{𝒙𝟑 = 𝟎}

Q 𝜋𝑄

{𝒙𝟏}

{𝒙𝟑}

⊔ ∅ {𝒙𝟐}

{𝒙𝟏 + 𝟐𝒙𝟑 ≤ 𝟐,

−𝒙𝟑 ≤ 𝟎,

𝒙𝟑 ≤ 𝟏}

∅

O 𝜋𝑂

{𝒙𝟏, 𝒙𝟑}

{𝒙𝟐}


{𝒙𝟏 − 𝒙𝟐 ≤ 𝟎,

𝒙𝟏 ≤ 𝟎}

{𝒙𝟑 = 𝟏}

P 𝜋𝑃

{𝒙𝟏, 𝒙𝟐}

{𝒙𝟑}

{𝒙𝟏 ≤ 𝟐}

{𝒙𝟑 = 𝟎}

Q 𝜋𝑄

{𝒙𝟏}

{𝒙𝟑}

⊔ ∅ {𝒙𝟐}

{𝒙𝟏 + 𝟐𝒙𝟑 ≤ 𝟐,

−𝒙𝟑 ≤ 𝟎,

𝒙𝟑 ≤ 𝟏}

∅

O 𝜋𝑂

{𝒙𝟏, 𝒙𝟑}

{𝒙𝟐}

𝜋𝑃 ⊔ 𝜋𝑄 = 𝜋𝑃 ≠ 𝜋𝑂


{𝒙𝟏 − 𝒙𝟐 ≤ 𝟎,

𝒙𝟏 ≤ 𝟎}

{𝒙𝟑 = 𝟏}

P 𝜋𝑃

{𝒙𝟏, 𝒙𝟐}

{𝒙𝟑}

{𝒙𝟏 ≤ 𝟐}

{𝒙𝟑 = 𝟎}

Q 𝜋𝑄

{𝒙𝟏}

{𝒙𝟑}

⊔ ∅ {𝒙𝟐}

{𝒙𝟏 + 𝟐𝒙𝟑 ≤ 𝟐,

−𝒙𝟑 ≤ 𝟎,

𝒙𝟑 ≤ 𝟏}

∅

O 𝜋𝑂

{𝒙𝟏, 𝒙𝟑}

{𝒙𝟐}


𝜋𝑃 ⊓ 𝜋𝑄 = 𝜋𝑄 ≠ 𝜋𝑂


{𝒙𝟏 − 𝒙𝟐 ≤ 𝟎,

𝒙𝟏 ≤ 𝟎}

{𝒙𝟑 = 𝟏}

P 𝜋𝑃

{𝒙𝟏, 𝒙𝟐}

{𝒙𝟑}

{𝒙𝟏 ≤ 𝟐}

{𝒙𝟑 = 𝟎}

Q 𝜋𝑄

{𝒙𝟏}

{𝒙𝟑}

⊔ ∅ {𝒙𝟐}

{𝒙𝟏 + 𝟐𝒙𝟑 ≤ 𝟐,

−𝒙𝟑 ≤ 𝟎,

𝒙𝟑 ≤ 𝟏}

∅

O 𝜋𝑂

{𝒙𝟏, 𝒙𝟑}

{𝒙𝟐}


𝜋𝑃 ⊓ 𝜋𝑄 = 𝜋𝑄 ≠ 𝜋𝑂

For Join, 𝜋𝑂 depends on both P and Q



Theorem: Let P and Q be two Polyhedra with the same permissiblepartition 𝜋 = {𝒳1, 𝒳2, . . . , 𝒳𝑟} and let 𝜋 be a permissible partition for the join, that is, 𝜋𝑃⊔𝑄 ⊑ 𝜋. If for any block 𝒳𝑘 ∈ 𝜋,𝑃𝑘 = 𝑄𝑘 , then 𝒳𝑘 ∈ 𝜋



x2

x1=4

x2=1

x2=2

x1=3

x1=1

x1=2

x2=4

x1=2x1

x2=-2x1+10

P

Q

x1P1

Q1

P2

Q2



x2

x1=4

x2=1

x2=2

x1=3

x1=1

x1=2

x2=4

x1=2x1

x2=-2x1+10

P

Q

x1P1

Q1

x2

x1=4

x2=1

x2=2

x1=4

x1=1

x1=1

x2=4

P

Q

x1P1

Q1

P2

Q2

P2

Q2

Operators with Permissible Partitions

Operators with Permissible Partitions

Theorem (permissible partition after join):

Let 𝜋 = 𝜋𝑃 ⊔ 𝜋𝑄 and 𝒰 = {𝒳𝑘 | 𝑃𝑘 = 𝑄𝑘 , 𝒳𝑘 ∈ 𝜋}.

Then 𝜋𝑃⊔𝑄 = 𝒰 ∪ ⨃𝒯∈𝜋 ∖𝒰𝒯 is permissible for 𝑃 ⊔ 𝑄

Theorem (permissible partition after meet):

𝜋𝑃 ⊔ 𝜋𝑄 is permissible for 𝑃 ⊓ 𝑄

Theorem (permissible partition after conditional):

If output O ≠⊥, then, 𝜋𝑃 ↑ ℬ is permissible for conditional

Theorem (permissible partition after assignment):

𝜋𝑃 ↑ ℬ is permissible for the output O of assignment

Asymptotic Complexity of Operators with Permissible Partitions

r: number

of blocks

Operator Before

(using both)

Our work

(using decomposition)

Join (⊔) Ο(𝑛𝑔) Ο(∑𝑖=1𝑟 𝑛𝑖𝑚𝑖𝑔𝑖 + 𝑛𝑚𝑎𝑥𝑚𝑚𝑎𝑥)

Meet (⊓) Ο(𝑛𝑚) Ο(∑𝑖=1𝑟 𝑛𝑖𝑚𝑖)

Inclusion (⊑) Ο(𝑛𝑔𝑚) Ο(∑𝑖=1𝑟 𝑛𝑖𝑚𝑖𝑔𝑖)

Assignment Ο(𝑛𝑔) Ο(𝑛𝑚𝑎𝑥𝑔𝑚𝑎𝑥)

Conditional Ο(𝑛) Ο(𝑛𝑚𝑎𝑥)

Conversion exp(n,g) exp(𝑛𝑚𝑎𝑥 , 𝑔𝑚𝑎𝑥)

Experimental Evaluation

We compared performance of ELINA against NewPolka and PPL

Using the Seahorn verification framework [CAV’15]• written in C, analyzes llvm-bitcode• produces Polyhedra invariants

> 1500 benchmarks from the software verification competition

Time limit: 4 hours

Memory limit: 12 GB





Evaluation

𝑛𝐸𝐿𝐼𝑁𝐴 < 𝑛𝑁𝑒𝑤𝑃𝑜𝑙𝑘𝑎 , large speedup as conversion is exponential in n

Related Work

Related Work

• Variable Packing • Blanchet et al. [PLDI’03]

• decomposition based on syntactic criteria

• loses precision

• Matrix based decomposition• Halbwachs et al. [FMSD’06]

• does not work with generators

• decomposition too coarse for join

Conclusion

Conclusion

Conclusion

Operator Both Online

decomposition

Join (⊔) Ο(𝑛𝑔) Ο(∑𝑖=1𝑟 𝑛𝑖𝑚𝑖𝑔𝑖

+ 𝑛𝑚𝑎𝑥𝑚𝑚𝑎𝑥)





Conclusion


decomposition







http://elina.ethz.ch


Conclusion


decomposition







http://elina.ethz.ch

Driver NewPolka PPL ELINA

500 var

39K LOC

OOM

(> 12 GB)

OOM

(> 12 GB)

4 sec

0.9 GB

650 var

25K LOC

TO

(> 4 hr)

TO

(> 4 hr)

2 sec

0.4 GB


Documents

Fast PolyhedraAbstract Domainelina.ethz.ch/slides/popl2017-fast-polyhedra.pdf · Polyhedra Domain Analysis Automatic Discovery of Linear Restraints Among Variables of a Program, POPL’78