A Tiling Perspective for Register Optimization

Register allocation is a much studied problem. A particularly important context for optimizing register allocation is within loops, since a significant fraction of the execution time of programs is often inside loop code. A variety of algorithms have been proposed in the past for register allocation, but the complexity of the problem has resulted in a decoupling of several important aspects, including loop unrolling, register promotion, and instruction reordering. In this paper, we develop an approach to register allocation and promotion in a unified optimization framework that simultaneously considers the impact of loop unrolling and instruction scheduling. This is done via a novel instruction tiling approach where instructions within a loop are represented along one dimension and innermost loop iterations along the other dimension. By exploiting the regularity along the loop dimension, and imposing essential dependence based constraints on intra-tile execution order, the problem of optimizing register pressure is cast in a constraint programming formalism. Experimental results are provided from thousands of innermost loops extracted from the SPEC benchmarks, demonstrating improvements over the current state-of-the-art

Design and Implementation of a Reversible Object-Oriented Programming Language

High-level reversible programming languages are few and far between and in general offer only rudimentary abstractions from the details of the underlying machine. Modern programming languages offer a wide array of language constructs and paradigms to facilitate the design of abstract interfaces, but we currently have a very limited understanding of the applicability of such features for reversible programming languages. We introduce the first reversible object-oriented programming language, ROOPL, with support for user-defined data types, class inheritance and subtype-polymorphism. The language extends the design of existing reversible imperative languages and it allows for effective implementation on reversible machines. We provide a formalization of the language semantics, the type system and we demonstrate the computational universality of the language by implementing a reversible Turing machine simulator. ROOPL statements are locally invertible at no extra cost to program size or computational complexity and the language provides direct access to the inverse semantics of each class method. We describe the techniques required for a garbage-free translation from ROOPL to the reversible assembly language PISA and provide a full implementation of said techniques. Our results indicate that core language features for object-oriented programming carries over to the field of reversible computing in some capacity.Comment: Master's Thesis, 110 pages, 55 figure