wala.util overview

This page provides high-level documentation for the com.ibm.wala.util sub-project of WALA. This is a work in progress!

Table of Contents

• Integer Sets
  • Union-Find
  • Mapping to integers
• Graphs
  • Data Structures
  • Graph Algorithms
• Fixed Point Solvers
  • General Infrastructure
    • Booleans and bit vectors
  • Dataflow Solver
• Tabulation Solver
• Other utilities
  • Collections
  • Progress monitors

Integer Sets

Union-Find

• IntegerUnionFind

Mapping to integers

Graphs

Data Structures

Graph Algorithms

Fixed Point Solvers

For many dataflow analyses, WALA provides specialized solvers that can be used directly. If you want to compute a dataflow analysis over a standard Killdall framework of an underlying flow graph and some transfer functions, use the specialized DataflowSolver type, which is documented below. For tabulation-style inter-procedural dataflow analyses (e.g., IFDS problems), use the tabulation solver (TODO: link to documentation). To use the WALA solver for other fixed-point problems, read on to learn about the more general infrastructure.

General Infrastructure

WALA's fixed-point solvers require a constraint system of com.ibm.wala.fixpoint.IFixedPointStatements over com.ibm.wala.fixpoint.IVariables. An IFixedPointStatement has a left-hand side (LHS) IVariable and a list of right-hand side (RHS) IVariables. A statement can be "evaluated" via com.ibm.wala.fixpoint.IFixedPointStatement.evaluate(), which typically involves computing a new state for its LHS variable based on the state of its RHS variables. (To this end, each IVariable must implement a com.ibm.wala.fixpoint.IVariable.copyState(T) method.) A fixed-point solver repeatedly evaluates statements until there is no further change, i.e., a fixed-point has been reached. Accordingly, statement evaluation must be monotonic.

The statements for a problem are collected in an com.ibm.wala.fixpoint.IFixedPointSystem, which gets solved by an com.ibm.wala.fixpoint.IFixedPointSolver. The outer logic for WALA's optimized fixed-point solver resides in com.ibm.wala.fixedpoint.impl.AbstractFixedPointSolver, and com.ibm.wala.fixedpoint.impl.DefaultFixedPointSystem provides a default implementation of IFixedPointSystem. The two are connected by com.ibm.wala.fixedpoint.impl.DefaultFixedPointSolver, which is the superclass of all fixed-point solvers used in other WALA components. To solve a fixed-point system, invoke com.ibm.wala.fixpoint.IFixedPointSolver.solve(IProgressMonitor).

In WALA, the logic for IFixedPointStatement evaluation typically resides in an com.ibm.wala.fixpoint.AbstractOperator object. WALA provides a com.ibm.wala.fixedpoint.impl.NullaryOperator type for statements with no RHS variables and a com.ibm.wala.fixpoint.UnaryOperator type for statements with a single RHS variable. When using WALA's optimized solver, fixed-point statements should not be allocated and added to the fixed-point system directly. Instead, use the appropriate variant of AbstractFixedPointSolver.newStatement(), depending on the number of RHS variables and arity of the operator.

Note that while solving a fixed-point system, statement evaluation is allowed to add new statements to the system. These statements are incorporated immediately and handled during the current solving phase. This functionality is useful, e.g., for techniques like on-the-fly call graph construction during points-to analysis.

Booleans and bit vectors

WALA provides the com.ibm.wala.fixpoint.BooleanVariable type for IVariables with boolean state. WALA also provides the com.ibm.wala.fixpoint.TrueOperator and com.ibm.wala.fixpoint.UnaryOr operators for constraints involving BooleanVariables.

The com.ibm.wala.fixpoint.BitVectorVariable type represents IVariables with bit-vector state. For efficiency, the state is represented using a MutableSharedBitVectorIntSet (see the integer set section). A number of operators on BitVectorVariables are provided as part of WALA's dataflow analysis framework; see below.

Dataflow Solver

Tabulation Solver

Other utilities

Collections

• Heap
• HashMapFactory / HashSetFactory
• Iterator2Collection, Iterator2Iterable

Progress monitors