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[avr-gcc-list] Unused registers?

From: Thomas Pircher
Subject: [avr-gcc-list] Unused registers?
Date: Wed, 21 Oct 2009 09:59:22 +0100 (BST)
User-agent: SquirrelMail/1.4.15

Hi all,

I came across a strange behaviour of avr-gcc. In one of our programs (4k
in Flash) the assembler code shows that the registers r2, r3, r5 and r6
are not used at all. Since we are (as everyone, I guess) short in code
space, I am wondering if there are some tricks that can make avr-gcc use
those registers, too.

I'm not saying avr-gcc has a bug, as those registers are used when I
compile other code.

Ideally, what I would like to know is if there is some special magic to
make avr-gcc use all available registers and reduce the code size enough
that we can squeeze in all the features asked for by marketing ;)

I'm using WinAVR 20071221 but 20090313 shows the same behaviour.

avr-size prog.elf
   text    data     bss     dec     hex filename
   4092       0      80    4172    104c prog.elf


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