Simple and effective link-time optimization of Modula-3 programs

Abstract

Modula-3 supports development of modular programs by separating an object's interface from its implementation. This separation induces a runtime overhead in the implementation of objects, because it prevents the compiler from having complete information about a program's type hierarchy. This overhead can be reduced at link time, when the entire type hierarchy becomes available. We describe opportunities for link-time optimization of Modula-3, present two link-time optimizations that reduce the runtime costs of Modula-3's opaque types and methods, and show how link-time optimization could provide C++ which the benefits of opaques types at no additional runtime cost.Our optimization techniques are implemented in mld, a retargetable linker for the MIPS, SPARC, and Intel 486, mld links a machine-independent intermediate code that is suitable for link-time optimization and code generation. Linking intermediate code simplifies implementation of the optimizations and makes it possible to evaluate them on a wide range of architectures. mld's optimizations are effective: they reduce the total number of instructions executed by up to 14% and convert as many as 79% of indirect calls to direct calls.