Chapter 4 Introduction

Morgan Kaufmann Publishers 31 January 2013Compiler/Hardware Speculationn Compiler can reorder instructionsn e.g., move load before branchn Can include “fix-up” instructionsto recover from incorrect guessn Hardware can look ahead for instructionsto executen Buffer resultsuntil it determines they are actually neededn Flush buffers on incorrect speculationCSE 420 Chapter 4 — The Processor — 109Speculation and Exceptionsn What if exception occurs on aspeculatively executed instruction?n e.g., speculative load before null-pointer checkn Static speculationn Can add ISA support for deferring exceptionsn Dynamic speculationn Can buffer exceptions until instructioncompletion (which may not occur)CSE 420 Chapter 4 — The Processor — 110