Walter Kirchgässner

An optimizer for Ada - design, experiences and results

In this paper we describe the design of a global machine independent low level optimizer for the Karlsruhe Ada Compiler. We give a short overview on the optimizations and data structures used in the optimizer as well as some experiences with the optimizer. Detailed measurements are provided for a collection of benchmarks. The average improvement of code speed is 40%.

Optimization in Ada

1. Introductio n Naive compilation of highly modular programs written i n high Level programming Languages usually results in grea t inefficiencies in object code. For this reason high Leve l languages are not used universally for programming. Since Ada is intended to be used in a wide range o f applications even in very time critical areas Like rea l time application, it will be necessary to bring th e efficiency of generated code into a tolerable range whe n compared with hand coded assembly programs. Within the Ada Project at the University of Karlsruhe w e have studied the applicability of classical optimizatio n techniques to Ada. An extended list of these techniques i s presented in CKirc827. For the analysis which underlies optimization, the progra m is first decomposed into basic blocks. A flow graph is the n constructed with the basic blocks building the nodes an d the flow of control (between the basic blocks) building th e edges. Based on this this flow graph data flow analysis an d optimization can be performed ECoMa80]. In this paper we want to study the influence of some Ad a features on flow analysis and thus optimization. Thes e features are exception handling, separate compilation , tasking, and generics. All citations are from the Ada Reference Manual (RM) CAdaS ]. 2. Exception s The exception facility in Ada deals with errors and othe r exceptional situations that arise during program execution. Such situations are called exception=. In the case of a program error (like arithmetic overflow) a predefined exception is raised. Predefined exceptions ca n be raised implicitly at almost any point of the program. Ada provides five predefined exceptions .