Maps: a Compiler-Managed Memory System for RAW Machines

• Authors: Agarwal Rajeev Barua Walter Lee Saman Amarasinghe Anant
• Venue: Maps: a Compiler-Managed Memory System for RAW Machines
• Year: 1998

Microprocessors of the next decade and beyond will be built using VLSI chips employing billions of transistors. In this generation of microprocessors, achieving a high level of parallelism at a reasonable clock speed will require full distribution of machine resources. Raw architectures explore this architectural space by distributing all their processor and memory resources as a 2-D mesh of simple tiles. To provide a simple sequential programming model, a Raw architecture exposes the hardware fully and relies on the compiler or the software run-time system to achieve efficient execution while maintaining the semantics of a single instruction stream and a unified memory system. Supporting a single view of memory on top of a distributed memory architecture presents a challenging compiler problem. This paper presents a compiler system called Maps that supports a unified view of memory on a Raw architecture. Maps relies on two inter-tile interconnects: a fast, statically schedulable network and a slower dynamic network. Maps attempts to schedule the memory accesses for maximum parallelism and speed while enforcing proper dependence. It optimizes for speed in two ways: by finding accesses that can be scheduled on the static interconnect through a process called {\it static promotion}, and by minimizing dependence sequentialization for the remaining accesses. Static accesses are discovered through applications of traditional pointer and array analysis, and a new technique called modulo unrolling. Maps enforces proper dependence through a combination of explicit synchronization and a technique called software serial ordering. We have implemented Maps based on the SUIF infrastructure. This paper presents preliminary results based on compiling several programs using Maps.