Chapter 4 Introduction

Morgan Kaufmann Publishers 31 January 2013Multiple Issuen Static multiple issuen Compiler groups instructions to be issued togethernnPackages them into “issue slots”Compiler detects and avoids hazardsn Dynamic multiple issuen CPU examines instruction stream andchooses instructions to issue each cyclen Compiler can help by reordering instructionsnCPU resolves hazardsusing advanced techniques at runtimeCSE 420 Chapter 4 — The Processor — 107Speculationn “Guess” what to do with an instructionn Start operation as soon as possiblenCheck whether guess was rightn If so, complete the operationn If not, roll-back and do the right thingn Common to static and dynamic multiple issuen ExamplesnnSpeculate on branch outcomenRoll back if path taken is differentSpeculate on loadn Roll back if location is updatedCSE 420 Chapter 4 — The Processor — 108