METHOD OF CONSTRUCTING A CONSTANT-FOLDING MECHANISM IN A MULTILANGUAGE OPTIMIZING COMPILER

摘要

Shoold not appear in this sectionA compiler framework uses a generic "shell" or control and sequencing mechanism, and a generic back end (where thecode generator is target-specific). The generic back end includes the functions of optimization, register and memory allocation,and code generation. The shell may be executed on various host computers, and the code generation function of the back end maybe targeted for any of a number of computer architectures. A front end is tailored for each different source language, such asCobol, Fortran, Pascal, C, C + +, Ada, etc. The front end scans and parses the source code modules, and generates from them anintermediate language ("IL") representation of the programs expressed in the source code. This IL is constructed to represent anyof the source code languages in a universal manner, so the interface between the front end and back end is of a standard format,and need not be rewritten for each language-specific front end. The IL representation by the front end is based upon atuple as the elemental unit, where each tuple represents a single operation to be performed, such as a load, a store, an add, alabel, a branch, etc. A data structure is created by the front end for each tuple, with fields for various necessary information. Onefeature of the invention is a mechanism for representing effects and dependencies in the interface between front end and backend; a tuple has an effect if it writes to memory, and has a dependency if it reads from a location which some other node maywrite to. A mechanism independent of source language is provided for describing the effects of program execution. Anotherfeature is the use in the optimization part of the compiler of a method for analyzing induction variables, where the improvement is touse the side effects sets used to construct IDEF sets. Another feature is a mechanism for "folding constants" (referred to asK-folding or a KFQLD routine), included as one of the optimizations. A further feature is the type definition mechanism, referredto as the TD module, which provides mechanisms used by the front end and the compiler of the back end in constructingprogram type information to be incorporated in an object module for use by a linker or debugger. Another feature is a method fordoing code generation using code templates in a multipass manner.