This paper describes a language-independent program representation-the program dependence graph—and &mCusses how program dependence graphs, together with operations such as program slicing, can provide the basis for powerfid programming tools that address important software-engineering problems, such as understanding what an existing program does and how it works, understanding the differences between several versions of a program, and creating new programs by combining pieces of old programs. The paper primarily surveys work in this mea that has been czried out at the University of Wisconsin during the past five years.

We present the design of DyC, a dynamic-compilation system for C based on run-time specialization. Directed by a few declarative user annotations that specify the variables and code on which dynamic compilation should take place, a binding-time analysis computes the set of run-time constants at each program point in the annotated procedure's control-flow graph; the analysis supports program-point-specific polyvariant division and specialization. The results of the analysis guide the construction of a run-time specializer for each dynamically compiled region; the specializer supports various caching strategies for managing dynamically generated code and mixes of speculative and demand-driven specialization of dynamic branch successors. Most of the key cost/benefit trade-offs in the binding-time analysis and the run-time specializer are open to user control through declarative policy annotations. DyC has

. This paper presents Soot, a framework for optimizing Java TM bytecode. The framework is implemented in Java and supports three intermediate representations for representing Java bytecode: Baf, a streamlined representation of Java's stack-based bytecode; Jimple, a typed three-address intermediate representation suitable for optimization; and Grimp, an aggregated version of Jimple. Our approach to class le optimization is to rst convert the stack-based bytecode into Jimple, a three-address form more amenable to traditional program optimization, and then convert the optimized Jimple back to bytecode. In order to demonstrate that our approach is feasible, we present experimental results showing the eects of processing class les through our framework. In particular, we study the techniques necessary to effectively translate Jimple back to bytecode, without losing performance. Finally, we demonstrate that class le optimization can be quite eective by showing the resul...

Text-based file comparators (e.g., the Unix utility diff), are very general tools that can be applied to arbitrary files. However, using such tools to compare programs can be unsatisfactory because their only notion of change is based on program text rather than program behavior. This paper describes a technique for comparing two versions of a program, determining which program components represent changes, and classifying each changed component as representing either a semantic or a textual change. ######################## This work was supported in part by the Defense Advanced Research Projects Agency, monitored by the Office of Naval Research under contract N00014-88-K, by the National Science Foundation under grant CCR8958530, and by grants from Xerox, Kodak, and Cray. Author's address: Computer Sciences Department, Univ. of Wisconsin, 1210 W. Dayton St., Madison, WI 53706. Permission to copy without fee all or part of this material is granted provided that the copies are not made...

This paper presents Soot, a framework for optimizing Java bytecode. The framework is implemented in Java and supports three intermediate representations for representing Java bytecode: Baf, a streamlined representation of bytecode which is simple to manipulate; Jimple, a typed 3-address intermediate representation suitable for optimization; and Grimp, an aggregated version of Jimple suitable for decompilation. We describe the motivation for each representation, and the salient points in translating from one representation to another. In order to demonstrate the usefulness of the framework, we have implemented intraprocedural and whole program optimizations. To show that whole program bytecode optimization can give performance improvements, we provide experimental results for 12 large benchmarks, including 8 SPECjvm98 benchmarks running on JDK 1.2 for GNU/Linuxtm . These results show up to 8% improvement when the optimized bytecode is run using the interpreter and up to 21% when run...

Current verification condition (VC) generation algorithms, such as weakest preconditions, yield a VC whose size may be exponential in the size of the code fragment being checked. This paper describes a two-stage VC generation algorithm that generates compact VCs whose size is worst-case quadratic in the size of the source fragment, and is close to linear in practice.This two-stage VC generation algorithm has been implemented as part of the Extended Static Checker for Java. It has allowed us to check large and complex methods that would otherwise be impossible to check due to time and space constraints.

Maintenance tends to degrade the structure of software, ultimately making maintenance more costly. At times, then, it is worthwhile to manipulate the structure of a system to make changes easier. However, it is shown that manual restructuring is an error-prone and expensive activity. By separating structural manipulations from other maintenance activities, the semantics of a system can be held constant by a tool, assuring that no errors are introduced by restructuring. To allow the maintenance team to focus on the aspects of restructuring and maintenance requiring human judgment, a transformation-based tool can be provided---based on a model that exploits preserving data flow-dependence and control flow-dependence---to automate the repetitive, errorprone, and computationally demanding aspects of re...

This thesis presents a framework for describing optimizations. It shows how to combine two such frameworks and how to reason about the properties of the resulting framework. The structure of the framework provides insight into when a combination yields better results. Also presented is a simple iterative algorithm for solving these frameworks. A framework is shown that combines Constant Propagation, Unreachable Code Elimination, Global Congruence Finding and Global Value Numbering. For these optimizations, the iterative algorithm runs in O(n^2) time. This thesis then presents an O(n log n) algorithm for combining the same optimizations. This technique also finds many of the common subexpressions found by Partial Redundancy Elimination. However, it requires a global code motion pass to make the optimized code correct, also presented. The global code motion algorithm removes some Partially Dead Code as a side-effect. An implementation demonstrates that the algorithm has shorter compile times than repeated passes of the separate optimizations while producing run-time speedups of 4%–7%. While global analyses are stronger, peephole analyses can be unexpectedly powerful. This thesis demonstrates parse-time peephole optimizations that find more than 95% of the constants and common subexpressions found by the best combined analysis. Finding constants and common subexpressions while parsing reduces peak intermediate representation size. This speeds up the later global analyses, reducing total compilation time by 10%. In conjunction with global code motion, these peephole optimizations generate excellent code very quickly, a useful feature for compilers that stress compilation speed over code quality.

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The ParaScope project is developing an integrated collection of tools to help scientific programmers implement correct and efficient parallel programs. The centerpiece of this collection is the ParaScope Editor, an intelligent interactive editor for parallel Fortran programs. The ParaScope Editor reveals to users potential hazards of a proposed parallelization in a program. It also provides a variety of powerful interactive program transformations that have been shown useful in converting programs to parallel form. In addition, the ParaScope Editor supports general user editing through a hybrid text and structure editing facility that incrementally analyzes the modified program for potential hazards. The ParaScope Editor is a new kind of program construction tool -- one that not only manages text, but also presents the user with information about the correctness of the parallel program under development. As such, it can support an exploratory programming style in which users get immediate feedback on their various strategies for parallelization.