A sufficiently smart compiler for procedural records

Many languages include a syntax for declaring programmer-defined structured data types, i.e., structs or records. R6RS supports syntactic record definitions but also allows records to be defined procedurally, i.e., via a set of run-time operations. Indeed, the procedural interface is considered to be the primitive interface, and the syntactic interface is designed to be macro expandable into code that uses the procedural interface. Run-time creation of record types has a potentially significant impact. In particular, record creation, field access, and field mutation cannot generally be open coded, as it can be with syntactically specified records. Often, however, the shape of a record type can be determined statically, and in such a case, performance equivalent to that of syntactically specified record types can be attained. This paper describes an efficient run-time implementation of procedural record types, discusses its overhead, and describes a set of compiler optimizations that eliminate the overhead when record-type information can be determined statically. The optimizations improve the performance of a set of representative benchmark programs by over 20% on average.