A technique is presented for global analysie of program structure in order to perform compile time optimization of object code generated for expressions. The global expression optimization presented includes constant propagation, common subexpression elimination, elimination of redundant register load operations, and live expression analysis. A general purpose program flow analysis algorithm is developed which depends upon the existence of an “optimizing function. ” The algorithm is defined formally using a directed graph model of program flow structure, and is shown to be correct, Several optimizing functions are defined which, when used in conjunction with the flow analysis algorithm, provide the various forms of code optimization. The flow analysis algorithm is sufficiently general that additional functions can easily be defined for other forms of globa ~ cod: optimization. 1. INTRODUCTION of the graph represent program control flow Dossi-A number of techniques have evolved for the bilities between the nodes at execution–time. compile-time analysis of program structure in order to locate redundant computations, perform constant

A fast algoritbm for finding dominators in a flowgraph is presented. The algorithm uses depth-first search and an efficient method of computing functions defined on paths in trees. A simple implemen-tation of the algorithm runs in O(m log n) time, where m is the number of edges and n is the number of vertices in the problem graph. A more sophisticated implementation runs in O(ma(m, n)) time, where a(m, n) is a functional inverse of Ackermann's function. Both versions of the algorithm were implemented in Algol W, a Stanford University version of Algol, and tested on an IBM 370/168. The programs were compared with an implementation by Purdom and Moore of a straightforward O(mn)-time algorithm, and with ~a bit vector algorithm described by Aho and Ullman. The fast algorithm beat the straightforward algorithm and the bit vector algorithm on all but the smallest graphs tested.

Historically, compilers have operated by applying a fixed set of optimizations in a predetermined order. We call such an ordered list of optimizations a compilation sequence. This paper describes a prototype system that uses biased random search to discover a program-specific compilation sequence that minimizes an explicit, external objective function. The result is a compiler framework that adapts its behavior to the application being compiled, to the pool of available transformations, to the objective function, and to the target machine.

We present two new data structure tools---disjoint set union with bottom-up linking, and pointer-based radix sort---and combine them with bottom-level microtrees to devise the first linear-time pointer-machine algorithms for off-line least common ancestors, minimum spanning tree (MST) verification, randomized MST construction, and computing dominators in a flowgraph.

A linear time algorithm is presented for finding dominators in control flow graphs.

The problem of finding the dominators in a control-flow graph has a long history in the literature. The original algorithms su#ered from a large asymptotic complexity but were easy to understand. Subsequent work improved the time bound, but generally sacrificed both simplicity and ease of implementation. This paper returns to a simple formulation of dominance as a global data-flow problem. Some insights into the natureofdominance lead to an implementation of an O(N )algorithm that runs faster, in practice, than the classic Lengauer-Tarjan algorithm, which has a timebound of O(E log(N)). We compare the algorithm to Lengauer-Tarjan because it is the best known and most widely used of the fast algorithms for dominance. Working from the same implementationinsights,wealso rederive (from earlier work on control dependence by Ferrante, et al.)amethodforcalculating dominance frontiers that we show is faster than the original algorithm by Cytron, et al. The aim of this paper is not to present a new algorithm, but, rather, to make an argument based on empirical evidence that algorithms with discouraging asymptotic complexities can be faster in practice than those more commonly employed. We show that, in some cases, careful engineering of simple algorithms can overcome theoretical advantages, even when problems grow beyond realistic sizes. Further, we argue that the algorithms presented herein are intuitive and easily implemented, making them excellent teaching tools.

Local register allocation (LRA) assigns pseudo-registers to actual registers in a basic block so as to minimize the spill cost. In this paper, four di#erent LRA algorithms are compared with respect to the quality of their generated allocations and the execution times of the algorithms themselves. The evaluation is based on a framework that views register allocation as the combination of boundary conditions, LRA, and register assignment. Our study does not address the problem of instruction scheduling in conjunction with register allocation, and we assume that the spill cost depends only on the number and type of load and store operations, but not on their positions within the instruction stream.

this article is organized as follows. Section 2 outlines Lengauer and Tarjan's approach. Section 3 gives a broad overview of our algorithm and dierentiates it from previous work. Section 4 presents our algorithm in detail, and Section 5 analyzes its running time. Section 6 presents our new path-compression result, on which the analysis relies. Section 7 describes our implementation, and Section 8 reports experimental results. We conclude in Section 9

Software engineering refers to the process of creating software systems. It applies loosely to techniques which reduce high software cost and complexity while increasing reliability and mochfiability. This paper outlines the procedures used in the development of computer software, emphasizing large-scale software development, and pmpomtmg areas

To my family, especially my wife Laura