Atmel CAVR-4 Manuale Utente

CAVR-4

Part1. Using the compiler

When clustering of variables is enabled, static and global variables are arranged so that 
variables that are accessed in the same function are stored close to each other. This 
makes it possible for the compiler to use the same base pointer for several accesses.

Note: This option has no effect at optimization levels None and Low.

Common code sequences are extracted to local subroutines. This optimization, which is 
performed at optimization level High, can reduce code size, sometimes dramatically, on 
behalf of execution time and stack size. The resulting code might however be difficult 
to debug. This optimization cannot be disabled using the 

#pragma optimize

 directive.

Note: This option has no effect at optimization levels None, Low, and Medium, unless 
the option 

--do_cross_call

 is used.

To read more about related command line options, see --no_cross_call, page 189, 
--do_cross_call, page 179, and --cross_call_passes, page 174.

For efficient treatment of data, you should consider the data types used and the most 
efficient placement of the data.This section provides useful information for efficient 
treatment of data:

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With the AVR IAR C/C++ Compiler there are three possible locations for storing 
strings:

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In external ROM in the data memory space

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In internal RAM in the data memory space

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In flash in the code memory space.

To read more about this, see Initialized data, page 39.