Discovering machine-specific code improvements

Abstract

I have designed and built a compiler construction tool that automates much of the case analysis necessary to exploit special purpose instructions on a target machine. Given a suitable description of the target machine, my analysis identifies instruction sequences that are equivalent to single instructions. During code generation, these equivalences can be used to avoid inefficient instruction sequences in favor of more efficient instructions. I present a working prototype of the instruction set analyzer needed in the framework outlined by [Giegerich 83]. In contrast to the work presented in [Davidson and Fraser 80, 84], I analyze machine descriptions during compiler construction, rather than analyzing instruction sequences that occur during code generation. [R Kessler 84] describes a system which analyzes machine descriptions during compiler construction, but which which is limited to discovering instructions that are equivalent to instruction sequences of length 2. The techniques presented here can identify instruction sequences of arbitrary length that are equivalent to single instructions. I have applied this analysis to the descriptions of two machines, and used the results to replace hand-written case analysis routines in an otherwise table-driven code generator [Henry 84].