Using an ML-Like Language to Specify the Semantics of Machine Instructions

Languages in the Computer Systems Description Languages (CSDL) family describe properties of machines. The descriptions are used to generate machine-dependent components of systems software. CSDL speciies instruction semantics using register transfer lists. Much information that is implicit in other register-transfer frameworks is explicit in CSDL. So much detail is required that it would be unrealistic to expect people to write these register transfers directly; a metalanguage is needed. The metalanguage, called-RTL, is based on ML. ML types and type inference are extended to provide polymorphism in \widths" as well as types, enabling the-RTL translator to infer much of the detail needed. Higher-order functions enable exploration and discovery of idioms that will be useful for specifying the semantics of machine instructions. ML extended with subtyping enables-RTL programmers to leave fetches implicit , resulting in a notation that is familiar to compiler writers and machine designers.-RTL contains polymorphic primitives in which the width of the result is independent of the width of an argument. Applying such primitives may result in terms with free \width variables." It would be counterpro-ductive to forbid such terms; they occur too frequently.-RTL typically constrains such variables, and it binds one by choosing the minimal integer satisfying the constraint.