machine designers have long recognized this dilemma. In 1972, Newey, Poole, and Waite [Newe79] observed that `Most problems will suggest a number of specialized operations which could possibly be implemented quite efficiently on certain hardware. The designer must balance the convenience and utility of these operations against the increased difficulty of implementing an abstract machine with a rich and varied instruction set.' Fortunately, applying all code improvements to the LIL removes efficiency considerations as HIL design issue. The abstract machine need only contain a set of features roughly equivalent to the intersection of the operations included in typical target machines. The result is a small, simple abstract machine. Such abstract machines are termed `intersection' machines. The analogy between union/intersection abstract machines and CISC/RISC architectures is obvious. void daxpy(n, da, dx, incx, dy, incy) int n, incx, incy; double da, dx[], dy[]; { if (n <= 0) return; i...

The functionality of the recently announced Microsoft .NET system is founded on the capabilities of the Common Language Infrastructure (CLI). Unlike some other recent systems based on virtual machines, the CLI was designed from the start to support a wide range of programming languages. It is also expected that ECMA standardization will make the CLI available on a wide range of computing platforms. This combination of multi-language capability and multiplatform implementation make the CLI an important target for future language compilers.

This article describes the key principles behind the design and implementation of a global code improver that has been use to construct several high-quality compilers and other program transformation and analysis tools. The code improver, called vpo, employs a paradigm of compilation that has proven to be flexible and adaptable---all code improving transformations are performed on a target-specific representation of the program. The aggressive use of this paradigm yields a code improver with several valuable properties. Four properties stand out. First, vpo is language and compiler independent. That is, it has been used to implement compilers for several different computer languages. For the C programming language, it has been used with several front ends each of which generates a different intermediate language. Second, because all code improvements are applied to a single low-level intermediate representation, phase ordering programs are minimized. Third, vpo is easily retargeted and handles a wide variety of architectures. In particular, vpo's structure allows new architectures and new implementations of existing architectures to be accommodated quickly and easily. Fourth and finally, because of its flexible structure, vpo has several other interesting uses in addition to its primary use in an optimizing compiler. This article describes the principles that have driven the design of vpo and the implications of these principles on vpo's implementation. The article concludes with a brief description of vpo's use as a back end with front ends for several different languages, and its use as a key component

: Many modern code generation methods use tree pattern matching with dynamic programming. However, especially in the case of an irregular special-purpose processor architecture their lack of transparency and stability may be problematic: it is difficult to predict the exact code generation result in advance, and the effects of a modification in the code generation rules may be surprisingly wide. In contrast, macro expansion techniques are intuitively transparent. When global variables are disallowed, macro expansion typically has the Church-Rosser property: the final expansion result is independent of the expansion order of the individual intermediate macro calls. Besides enabling parallel implementation, order-independence means stability: the effects of modifying a macro definition are guaranteed to remain local. The locality is actually the problem with macro expansion; code optimization is improved when an assembly language macro is sensitive to its context. For instance, it should...

Virtualization is ubiquitous, with the global availability of the Java Virtual Machine and other similar virtual machine platforms. Higher-order

This dissertation was presented by