A portable and optimizing back end for the SML/NJ compiler

Abstract

There are two major goals that must be addressed in a portable back end: a good sequence of instructions must be selected making full use of the capabilities of the machine, and it must be possible to orchestrate target-specific optimizations. A key to the first problem is the language MLRISC, intended in part, to represent the simplest and most basic operations implementable in hardware. The importance of MLRISC is that it provides a common representation for expressing the instruction set of any hardware platform. Bottom-up tree pattern matching with dynamic programming, expressed using succinct and clear specifications of the target instruction set, is used to generate target machine code from an MLRISC program. Target-specific optimizations are performed by parameterizing off-the-shelf optimization modules with concepts common across architectures. The specification of a variety of architectures, and the ability to mix and match sophisticated optimization algorithms are shown. The resulting back end is independent of the intermediate language used in SML/NJ, and could in principle be used in a compiler for a source language quite different from SML. We argue that porting the compiler to a new architecture requires substantially less effort than the existing abstract machine approach, and report significant gains from preliminary architecture description driven optimizations.

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