Re: [avr-gcc-list] __builtin_constant_p for inline func args with -Os

[Paul Stoffregen]

Thanks!  That works perfectly.  :-)

I was totally misunderstanding the problem.  Just one little attribute, 
but it's a huge help.

Thanks again. 


-Paul



Joerg Wunsch wrote:
> Paul Stoffregen <address@hidden> wrote:
>
>   
> > Indeed it works great with -O2.  But with -Os, __builtin_constant_p
> > never returns 1.
> >     
>
> It appears to me GCC simply thinks inlining the function would not be
> feasible with -Os -- well, partially at least.  If you declare your
> function as
>
> static inline void __attribute__((always_inline))
> digitalWrite(uint8_t pin, uint8_t val)
>
> (thus overriding GCC's heuristics about inlining), it yields your
> desired result:
>
> main:
> /* prologue: function */
> /* frame size = 0 */
>         sbi 43-32,2
>         lds r24,num
>         ldi r22,lo8(1)
>         call _digitalWrite
>         sbi 43-32,2
> ..L2:
>         rjmp .L2
>
>