Modifying code after the compiler has generated it can be useful for both optimization and instrumentation. This paper compares the code modification systems of Mahler and pixie, and describes two new systems we have built that are hybrids of the two. This paper covers material presented at the CODE '91 International Workshop on Code Generation, Schloss Dagstuhl, Germany, May 20-24, 1991. i 1. Introduction Late code modification is the process of modifying the output of a compiler after the compiler has generated it. The reasons one might want to do this fall into two categories, optimization and instrumentation. Some forms of optimization must be performed on assembly-level or machinelevel code. The oldest is peephole optimization [11], which acts to tidy up code that a compiler has generated; it has since been generalized to include transformations on more machine-independent code [2,3]. Reordering of code to avoid pipeline stalls [4,7,18] is most often done after the code is gene...

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We built a system in which the compiler back end and the linker work together to present an abstract machine at a considerably higher level than the actual machine. The intermediate language translated by the back end is the target language of all high-level compilers and is also the only assembly language generally available. This lets us do intermodule register allocation, which would be harder if some of the code in the program had come from a traditional assembler, out of sight of the optimizer. We do intermodule register allocation and pipeline instruction scheduling at link time, using information gathered by the compiler back end. The mechanism for analyzing and modifying the program at link time was also useful in a wide array of instrumentation tools. i 1. Introduction When our lab built its experimental RISC workstation, the Titan, we defined a high-level assembly language as the official interface to the machine. This high-level assembly language, called Mahler,...

Development of reusable software is an important software-engineering problem. Researchers address this problem by designing programming languages with features to support the development of modular software. Object-oriented languages support modularity by providing abstractions, such as Modula-3's abstract data types, that separate a software component's interface from its implementation. Some object-oriented features, however, incur runtime costs, because they shift binding time, which is the time when the complete representations of types and variables are known, from compile time to run time. Late binding makes it difficult for a compiler to implement these features efficiently. This thesis describes a software approach to the problem of implementing high-level programming languages with late binding. We show how Modula-3's and C++'s features that require late binding can be implemented more efficiently with an optimizing linker. We describe the design and implementation of m...

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