Frances E. Allen

Control flow analysis

Any static, global analysis of the expression and data relationships in a program requires a knowledge of the control flow of the program. Since one of the primary reasons for doing such a global analysis in a compiler is to produce optimized programs, control flow analysis has been embedded in many compilers and has been described in several papers. An early paper by Prosser [5] described the use of Boolean matrices (or, more particularly, connectivity matrices) in flow analysis. The use of “dominance” relationships in flow analysis was first introduced by Prosser and much expanded by Lowry and Medlock [6]. References [6,8,9] describe compilers which use various forms of control flow analysis for optimization. Some recent developments in the area are reported in [4] and in [7]. The underlying motivation in all the different types of control flow analysis is the need to codify the flow relationships in the program. The codification may be in connectivity matrices, in predecessor-successor tables, in dominance lists, etc. Whatever the form, the purpose is to facilitate determining what the flow relationships are; in other words to facilitate answering such questions as: is this an inner loop?, if an expression is removed from the loop where can it be correctly and profitably placed?, which variable definitions can affect this use? In this paper the basic control flow relationships are expressed in a directed graph. Various graph constructs are then found and shown to codify interesting global relationships.

A program data flow analysis procedure

The global data relationships in a program can be exposed and codified by the static analysis methods described in this paper. A procedure is given which determines all the definitions which can possibly “reach” each node of the control flow graph of the program and all the definitions that are “live” on each edge of the graph. The procedure uses an “interval” ordered edge listing data structure and handles reducible and irreducible graphs indistinguishably.

An overview of the PTRAN analysis system for multiprocessing

PTRAN (Parallel TRANslator) is a system for automatically restructuring sequential FORTRAN programs for execution on parallel architectures. This paper describes PTRAN-A: the currently operational analysis phase of PTRAN. The analysis is both broad and deep, incorporating interprocedural information into dependence analysis. The system is organized around a persistent database of program and procedure information. PTRAN incorporates several new, fast algorithms in a pragmatic design.

An overview for the PTRAN analysis system for multiprocessing

PTRAN (Parallel TRANslator) is a system for automatically restructuring sequential FORTRAN programs for execution on parallel architectures. This paper describes PTRAN-A: the currently operational analysis phase of PTRAN. The analysis is both broad and deep, incorporating interprocedural information into dependence analysis. The system is organized around a persistent database of program and procedure information. PTRAN incorporates several new, fast algorithms in a pragmatic design.

A framework for determining useful parallelism

An approach to finding and forming parallel processes for both sequential and parallel programs is presented. The approach is presented in a framework that can create useful parallelism for a variety of parallel architectures. The framework makes use of a control dependence graph to capture maximal parallelism, a process tree to expose useful parallelism, renaming and storage segregation to reduce data dependencies, and an architecture-specific cost analyzer to evaluate the effectiveness of the potential processes. The framework is currently being implemented.

The experimental compiling system

The Experimental Compiling System (ECS) described here represents a new compiler construction methodology that uses a compiler base which can be augmenttd to create a compiler for any one of a wide class of source languages. The resulting compiler permits the user to select code quality ranging from highly optimized to interpretive. The investigation is concentrating on easy expression and efficient implementation of language semantics; syntax analysis is ignored.

The history of language processor technology in IBM

The history of language processor technology in IBM is described in this paper. Most of the paper is devoted to compiler technology; interpreters, assemblers, and macro systems are discussed briefly. The emphasis is on scientific contributions and technological advances from ah istorical perspective. The synergistic relationship between theory andpractice is a subtheme.

Interprocedural Analysis and the Information derived by it

Well structured programs are usually expressed as a system of functionally oriented procedures. By analyzing and transforming an entire system of procedures, linkages can be modified or eliminated and interprocedural data dependencies documented to the user. This paper presents some of the methods being developed to effect such interprocedural analysis and transformations.

A technological review of the FORTRAN I compiler

The FORTRAN I compiler functions and organizations are described and shown to form the basis for many of the techniques used in modern compilers.

Turning points in interaction with computers

The development of interfaces by which humans and computers interact has brought about some of the most significant turning points in computing in the last 38 years. The work on interfaces in programming languages, office automation, and human factors has enabled more and more people to interact effectively with computers, but there is more work to do. The IBM Systems Journal has published many papers that reflect results of work in this area, and readers can see a representative selection of those papers in this section of this issue.