[avr-gcc-list] Unnecessary mov to temp register in inline funct.

[Christian Vogel]

Hi,

I have a simple routine to send a char out of the uart:

> inline void send_char_uart(unsigned char c){
>   while(! (USR & BV(UDRE)) ); /* wait until last char is gone */
>   UDR = c;                    /* send char out of serial port */
> }

Now if I call this in another routine, the data is first moved from
the original register to a temp register and then out'ed to UDR:
(comments by myself, assembly code by gcc version 3.3 20021111 (experimental).
(rpm by address@hidden, many thanks!):

  mov  r24,r21  ; data32_0(r21) --> r24
  sbis 0x0b,5   ; <--+
  rjmp .-4      ; ---+ while(! USR & BV(UDRE) );
  out  0x06,r24 ; r24 --> UDR

What I would preferrably use is just out 0x06,r21 and forget the first mov.

Can I do something (besides making this short function a #define, this
get's rid of the temp register) to make this inline-function not use the
temp-register or is the assemly of an inline function fixed as soon
as it's defined so gcc really *HAS* to use this fixed register r24?

        Chris

---- just for reference, a snippet of my main program ---
     (which just read data from a ADC and outputs it to
      my computer's serial port)

> /* access variable as 32 bit or 4x 8 bit */
> typedef union {
>   uint32_t data32;      /* later: r18..21 */
>   struct {
>      uint8_t data32_0;  /* later:  r18 */
>      uint8_t data32_1;  /* later:  r19 */
>      uint8_t data32_2;  /* later:  r20 */
>      uint8_t data32_3;  /* later:  r21 */
>   };
> } union32_t;

> int main(void){
>   register union32_t data;
>   (...)
>   send_char_uart(data.data32_3); /* mov r24,r21 ... */
>   send_char_uart(data.data32_2); /* mov r24,r20 ... */
>   send_char_uart(data.data32_1); /* mov r24,r19 ... */
>   send_char_uart(data.data32_0); /* mov r24,r18 ... */
> }

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