2017-02-06 14:03 GMT+04:00 Georg-Johann Lay <a...@gjlay.de>:
> This patch adds an alternative to addhi3_zero_extend for the case
> where output operand and the 8-bit addend happen to reside
> the the same register. Without the patch this might lead
> to additional reloads to satisfy the constraints like
>
>
> uint16_t func (uint8_t x, uint16_t y)
> {
> return x + y;
> }
>
>
> Without the new alternative the code will be
>
>
> func:
> movw r18,r22 ; 18 *movhi/1 [length = 1]
> add r18,r24 ; 13 *addhi3_zero_extend [length = 2]
> adc r19,__zero_reg__
> movw r24,r18 ; 19 *movhi/1 [length = 1]
> /* epilogue start */
> ret
>
>
> With the change the code reads
>
>
> func:
> add r24,r22 ; 13 *addhi3_zero_extend/2 [length = 3]
> mov r25,r23
> adc r25,__zero_reg__
> /* epilogue start */
> ret
>
> which has smaller code size and register pressure.
>
> Ok for trunk?
>
> Johann
>
> * config/avr/avr.md (*addhi3_zero_extend): Add alternative where
> REGNO($0) == REGNO($1).
Approved.
Please apply.
