Constraint Solver¶

The constraint solver subsystem is aimed to provide the possibility to automatically generate test cases based on specified constraints. A constraint is represented by a set of limitations for input values. The solver finds values of input variables which will violate the limitations if there are any such values.

The subsystem uses a third-party SMT solver as an engine (in the current version, we use the Z3 solver by Microsoft Research). SMT solvers use a special functional language to specify constraints. The subsystem generates constructions in the SMT language and uses the engine to process them and produce the results (find values of unknown input variables).

Syntax trees¶

We use language-independent syntax trees to represent constraints. These trees then are processed to generate a representation that can be understood by a particular SMT solver. The syntax tree contains the following node types:

1. Constraint. This is the root node of the tree. It holds the list of unknown variables and the list of limitations for these variables.
2. Formula. Represents a limitation expression. Can be combined with other limitations to build a more complex limitation (by applying a logic OR, AND or NOT to it). The underlying expression must be a logic expression that can be solved to true or false.
3. Operation. Represents an unary or binary operation with some unknown variable, some value or some expression as parameters.
4. Variable.Represents an input variable. It can have an assigned value and, in such case, will be treated as a value. Otherwise, it is an unknown variable. A variable includes a type as an attribute.
5. Value. Specifies some known value of the specified type which can be accessed as an attribute.

Note: Operation, Variables and Value can be treated polymorphically as syntax elements (SyntaxElement). This allows combining them to build complex expressions.

The current implementation supports operations with the following data types:

1. Bit vectors
2. Booleans

Constraint Solver Java Library¶

The source code files of the Constraint Solver subsystem are located in the "microtesk++/constraint-solver" folder. The java classes are organized in the following packages:

1. ru.ispras.microtesk.constraints - contains SMT representation generation logic and solver implementations.
2. ru.ispras.microtesk.constraints.syntax - contains classes implementing syntax tree nodes.
3. ru.ispras.microtesk.constraints.syntax.types - contains code that specifies particular data types and operation types.
4. ru.ispras.microtesk.constraints.tests - contains JUnit test cases.

База данных ограничений¶

База данных ограничений строится автоматически в результате анализа формализованных спецификаций системы команд микропроцессора, выполненной на одном из ADL-языков (например, nML). Некоторые ситуации могут описываться вручную и добавляться в базу данных ограничений.