Scope & Data-flow browsing

Overview

The Scope plug-in computes information about dependencies on a user-specified lvalue D at a user-specified program point L. It provides the following three features, which are presented in greater detail below.

• ShowDefs: gives information about the statements that may contribute to the value of D at L;

• DataScope: shows the statements where D is guaranteed to have the same value than at L;

• Zones: shows which data is needed in the previous statements to compute D at L.

Show Defs

ShowDefs selects the statements that contribute to define the value of D at L, and prints a message if a part of D might be undefined. Notice that undefined here only means that it has not been defined on some path from the beginning of the function.

DataScope

DataScope selects sets of statements around a user-specified program point L where a user-specified lvalue D is guaranteed to have the same value than at L.

• Backward selected statements are colored in green: if a statement s belongs to this selection, then for all executions of the function, the value of D is not modified between the execution of s and the next time L is reached.

• Forward selected statements are colored in blue: if a statement s belongs to this selection, then for all executions of the function, the value of D is not modified between the last time L is reached and the time s is reached.

• Statements that are in both selections are colored in purple.

• The starting statement is underlined and is always part of the forward set.

Zones

Zones computes, for each point Li of the function, the data Di needed to know the value of D at L. After this computation, the result Di will be printed in the information window each time a statement Li is selected. Of course, the only interesting program points Li are the ones reached before L.

The statements that contribute to the computation are highlighted so that you should get the same result Di for successive statements that are not highlighted.

Usage

Those features are available through the graphical user interface once the value analysis (Eva plug-in) has been done. They can be called from the menu Dependencies in the popup menu that appears when right-clicking a statement:

• The program point L is the one before the selected statement;

• The lvalue D for which computations are done is either the one that is currently selected, if any, or an lvalue entered by the user in a dialog window.

Results are presented by coloring the statements in the graphical interface as explained above. In addition, when something has been selected through these dependency features, a message in the information window serves as a reminder of where it comes from.

Note that all the variables that appear in the user-provided lvalue are taken into account, so that selecting T[0] and T[i] might lead to different results, even if the analysis is performed at a point where i=0.

Dependencies

The Scope plug-in only takes into account the executions that have been considered by Eva. In particular, the alarms emitted by Eva may correspond to executions that it ceased to consider. The alarms emitted by Eva should therefore be carefully examined by the user.