Analysis of Control Flow and Data Flow

Abstract

In this chapter, we analyze the control flow and dataflow of a C program. Understanding these properties helps a designer to understand the relationship between a C program and an equivalent hardware implementation of that C program. Control edges and data edges reflect relationships between the operations of the C program, and we distinguish control edges from data edges. A control edge specifies the execution order of these operations. A data edge specifies that data produced by one operation is consumed by the second. By representing the operations of the C program as nodes of a graph, control edges and data edges define a structure called a Control Flow Graph (CFG) and a Data Flow Graph (DFG), respectively. For a hardware–software codesigner, the distinction between control edges and data edges is of great importance. Data edges will appear in any implementation target – hardware or software – of the algorithm. Control edges, on the other hand, may be removed when the algorithm executes on an architecture with sufficient implementation parallelism.