Automatic generation of fast optimizing code generators

Abstract

This paper describes a system that accepts compact specifications of an intermediate code and target machine and produces program code for an integrated code generator and peephole optimizer. A compiler for most of C uses this packa.ge. It emits code comparable to PCCI’S, but it runs over five times faster on preliminary benchmarks. This compiler also runs over twice as fast as a version of pcc2 with a hand-coded, VAX-specific code generator. The code generators are produced as follows. A programmer describes a naive code generator by means of a non-procedural specification. The programmer also prepares a machine description for a retargetable peephole optimizer [2]. These two systems are used together to compile a testbed, and the compiler records each peephole optimization as it is made. This record and the specification of the naive code generator are compiled into a fast, integrated code generator and optimizer. This production code generator then takes the place of the slower “training” version. The production code generator and optimizer are integrated to the point that the code to be generated is communicated from one to the other by encoding it in the program counter, which obviates most inter-phase communication costs. Interpretive peephole optimizers have been driven by traces from retargetable peephole optimizers [3] and integrated with interpretive code generators [4], but the current work is distinguished by the production of a hard-coded, optimizing code generator. Historically, retargetable code generators (i.e., those not largely rewritten for each new machine)