[Bug optimization/10620] for(i=25000;i;i--) {} generates wrong assembly source in avr-gcc with -O2

[gumo@lucifer.kgt.bme.hu]

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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=10620



------- Additional Comments From gumo@lucifer.kgt.bme.hu  2003-05-23 07:51 -------
Subject: Re: [Bug optimization/10620] for(i=25000;i;i--) {} generates wrong
 assembly source in avr-gcc with -O2

Hi,

> I certainly don't know much about avr asm. With gcc 3.2.3 and 3.3 branch, I see the same code
> that you mention (.L10 etc.) generated. With mainline (20030520), I see the following:
>
> .L8:
>         subi r18,lo8(-(-50))
>         sbci r19,hi8(-(-50))
>         brne .L8
>
> Is this assembly also faulty? Thanks,

Yes. The original C code is i--, so it should decrease the register pair
by 1:

        subi r18,lo8(-(-1))
        sbci r19,hi8(-(-1))

Thanks,
Gumo




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