In optimizing compilers, data structure choices directly influence the power and efficiency of practical program optimization. A poor choice of data structure can inhibit optimization or slow compilation to the point that advanced optimization features become undesirable. Recently, static single assignment form and the control dependence graph have been proposed to represent data flow and control flow propertiee of programs. Each of these previously unrelated techniques lends efficiency and power to a useful class of program optimization. Although both of these structures are attractive, the difficulty of their construction and their potential size have discouraged their use. We present new algorithms that efficiently compute these data structures for arbitrary control flow graphs. The algorithms use dominance frontiers, a new concept that may have other applications. We also give analytical and experimental evidence that all of these data structures are usually linear in the size of the original program. This paper thus presents strong evidence that these structures can be of practical use in optimization.

We present practical approximation methods for computing interprocedural aliases and side effects for a program written in a language that includes pointers, reference parameters and recursion. We present the following results: 1) An algorithm for flow-sensitive interprocedural alias analysis which is more precise and efficient than the best interprocedural method known. 2) An extension of traditional flow-insensitive alias analysis which accommodates pointers and provides a framework for a family of algorithms which trade off precision for efficiency. 3) An algorithm which correctly computes side effects in the presence of pointers. Pointers cannot be correctly handled by conventional methods for side effect analysis. 4) An alias naming technique which handles dynamically allocated objects and guarantees the correctness of data-flow analysis. 5) A compact representation based on transitive reduction which does not result in a loss of precision and improves precision in some cases. 6)...

The first interprocedural modification side-effects analysis for C (MOD_C) that obtains better than worst-case precision on programs with general-purpose pointer usage is presented with empirical results. The analysis consists of an algorithm schema corresponding to a family of MODC algorithms with two independent phases: one for determining pointer-induced aliases and a subsequent one for propagating interprocedural side effects. These MOD_C algorithms are parameterized by the aliasing method used. The empirical results compare the performance of two dissimilar MOD_C algorithms: MOD_C(FSAlias) uses a flow-sensitive, calling-context-sensitive interprocedural alias analysis [LR92]; MOD_C(FIAlias) uses a flow-insensitive, calling-context-insensitive alias analysis which is much faster, but less accurate. These two algorithms were profiled on 45 programs ranging in size from 250 to 30,000 lines of C code, and the results demonstrate dramatically the possible cost-precision tradeoffs. This first comparative implementation of MODC analyses offers insight into the differences between flow-/context-sensitive and flow-/context-insensitive analyses. The analysis cost versus precision tradeoffs in side-effect information obtained is reported. The results show surprisingly that the precision of flow-sensitive side-effect analysis is not always prohibitive in cost, and that the precision of flow-insensitive analysis is substantially better than worst-case estimates and seems sufficient for certain applications. On average MODC (FSAlias) for procedures and calls is in the range of 20% more precise than MODC (F IAlias); however, the performance was found to be at least an order of magnitude slower than MODC (F IAlias).

this article, we describe approximation methods for computing interprocedural aliases for a program written in a language that includes pointers, reference parameters, and recursion. We present the following contributions:

This paper presents a general framework for determining average program execution times and their variance, based on the program's interval structure and control dependence graph. Average execution times and variance values are computed using frequency information from an optimized counter-based execution profile of the program. 1 Introduction It is important for a compiler to obtain estimates of execution times for subcomputations of an input program, if it is to attempt optimizations related to overhead values in the target architecture. In earlier work [SH86a, SH86b, Sar87, Sar89], we used estimates of execution times to facilitate the automatic partitioning and scheduling of programs written in the singleassignment language, Sisal, for parallel execution on multiprocessors. In this paper, we present a general framework for estimating average execution times in a program. This approach is based on the interval structure [ASU86] and the control dependence relation [FOW87], both of w...

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...

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. Data-flow analysis algorithms can be classified into two categories: flow-sensitive and flow-insensitive. To improve efficiency, flowinsensitive interprocedural analyses do not make use of the intraprocedural control flow information associated with individual procedures. Since pointer-induced aliases can change within a procedure, applying known flow-insensitive analyses can result in either incorrect or overly conservative solutions. In this paper, we present a flow-insensitive dataflow analysis algorithm that computes interprocedural pointer-induced aliases. We improve the precision of our analysis by (1) making use of certain types of kill information that can be precomputed efficiently, and (2) computing aliases generated in each procedure instead of holding at the exit of each procedure. We improve the efficiency of our algorithm by introducing a technique called deferred evaluation. Interprocedural analyses, including alias analysis, rely upon the program call graph (PCG) fo...

This dissertation addresses a number of important issues related to interprocedural optimization. Interprocedural optimization is an integral component in a compilation system for high-performance computing. The importance of interprocedural optimization stems from two sources: it increases the context available to the optimizing compiler, and it enables programmers to use procedure calls without the concern of hurting execution time. While important, interprocedural optimization can introduce some significant compile-time costs. When interprocedural information is used to optimize a procedure, the procedure is then dependent on those interprocedural facts. Thus, even if the procedure is not edited, it may require recompilation due to changes in the interprocedural facts. In addition to these effects on recompilation, interprocedural information can also be expensive to compute. Furthermore, interprocedural optimizations can increase program size which can in turn increase compile tim...

The dependencies that exist among definitions and uses of variables in a program are required by many language-processing tools. This paper considers the computation of definition-use and use-definition chains that extend across procedure boundaries at call and return sites. Intraprocedural definition and use information is abstracted for each procedure and is used to construct an interprocedural flow graph. This intraprocedural data-flow information is then propagated throughout the program via the interprocedural flow graph to obtain sets of reaching deilnitions and/or reachable uses for each interprocedural control point, including procedure entry, exit, call, and return. Interprocedural definition-use and/or use-definition chains are computed from this reaching information. The technique handles the interprocedural effects of the data flow caused by both reference parameters and global variables, while preserving the calling context of called procedures. Additionally, recursion, aliasing, and separate compilation are handled. The technique has been implemented using a Sun-4 Workstation and incorporated into an interprocedural data-flow tester. Results from experiments indicate the practicality of the technique, both