AMD Typewriter x86 사용자 설명서

AMD

Contents

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22007E/0—November 1999

AMD Athlon™ Processor x86 Code Optimization

Contents

Revision History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xv

Introduction

About this Document . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

AMD Athlon™ Processor Family. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

AMD Athlon Processor Microarchitecture Summary . . . . . . . . . . . . . 4

Top Optimizations

Optimization Star . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Group I Optimizations — Essential Optimizations . . . . . . . . . . . . . . . 8

Memory Size and Alignment Issues . . . . . . . . . . . . . . . . . . . . . . 8

Use the 3DNow!™ PREFETCH and PREFETCHW
Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Select DirectPath Over VectorPath Instructions . . . . . . . . . . . 9

Group II Optimizations—Secondary Optimizations . . . . . . . . . . . . . . 9

Load-Execute Instruction Usage. . . . . . . . . . . . . . . . . . . . . . . . . 9

Take Advantage of Write Combining. . . . . . . . . . . . . . . . . . . . 10

Use 3DNow! Instructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Avoid Branches Dependent on Random Data . . . . . . . . . . . . . 10

Avoid Placing Code and Data in the Same
64-Byte Cache Line. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

C Source Level Optimizations

Ensure Floating-Point Variables and Expressions
are of Type Float . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Use 32-Bit Data Types for Integer Code . . . . . . . . . . . . . . . . . . . . . . . 13

Consider the Sign of Integer Operands . . . . . . . . . . . . . . . . . . . . . . . 14

Use Array Style Instead of Pointer Style Code . . . . . . . . . . . . . . . . . 15

Completely Unroll Small Loops. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Avoid Unnecessary Store-to-Load Dependencies . . . . . . . . . . . . . . . 18

Consider Expression Order in Compound Branch Conditions . . . . . 20