Atmel CAVR-4 사용자 설명서

CAVR-4

Taking advantage of the compilation system

Reference Guide

The AVR IAR C/C++ Compiler allows you to specify whether generated code should 
be optimized for size or for speed, at a selectable optimization level. The purpose of 
optimization is to reduce the code size and to improve the execution speed. When only 
one of these two goals can be reached, the compiler prioritizes according to the settings 
you specify. Note that one optimization sometimes enables other optimizations to be 
performed, and an application may become smaller even when optimizing for speed 
rather than size.

The following table describes the optimization levels:

By default, the same optimization level for an entire project or file is used, but you 
should consider using different optimization settings for different files in a project. For 
example, put code that must execute very quickly into a separate file and compile it for 
minimal execution time (maximum speed), and the rest of the code for minimal code 
size. This will give a small program, which is still fast enough where it matters. The 

#pragma

 

optimize

 directive allows you to fine-tune the optimization for specific 

functions, such as time-critical functions.

A high level of optimization will result in increased compile time, and may also make 
debugging more difficult, since it will be less clear how the generated code relates to the 
source code. At any time, if you experience difficulties when debugging your code, try 
lowering the optimization level.

None (Best debug support)

Variables live through their entire scope

Low

Dead code elimination

Redundant label elimination

Redundant branch elimination

Medium

Live-dead analysis and optimization

Code hoisting

Register content analysis and optimization

Code motion

Common subexpression elimination

Clustering of variables

High (Maximum optimization)

Peephole optimization

Cross jumping

Cross call (when optimizing for size)

Function inlining

Type-based alias analysis