Re: [avr-libc-dev] [bugs #12040] sbi in FAQ

[John Altstadt]

Erik Walthinsen wrote:
> > Should be removed or replaced with "The compiler optimizes '|=' to use
> > sbi when appropriate" (does he?)
>
>
> Just to clarify, no it does not (avr-gcc-3.4.3, as built by rod.info's 
> script, aka a very recent stable compiler used by the vast majority of 
> people actually making products):
>
>    4:test.c        ****   PORTB |= 0x03;
>   67                    .LM2:
>   68 0008 88B3                  in r24,56-0x20
>   69 000a 8360                  ori r24,lo8(3)
>   70 000c 88BB                  out 56-0x20,r24
>
> vs.
>
>    4:test.c        ****   PORTB |= 0x01;
>   67                    .LM2:
>   68 0008 C09A                  sbi 56-0x20,0
>    5:test.c        ****   PORTB |= 0x02;
>   70                    .LM3:
>   71 000a C19A                  sbi 56-0x20,1
>
> This insistence on people using the least readable form of all possible 
> ways of doing bit manipulation because the compiler is really smart 
> doesn't seem to have actual grounding.

Out of curiosity on my part, why do you think that
   PORTB |= 0x03;
and
   PORTB |= 0x01;
   PORTB |= 0x02;
are equivalent statements?

John