Re: [avr-gcc-list] Problem With Call to Mulsi3

[Thomas D. Dean]

On Mon, 2009-02-16 at 23:37 +0100, Georg-Johann Lay wrote:

>         distance = =895*distance;

See my followup message about the typo. 
          distance = 895*distance.

> 
> [...]
> 
>  > 895*distance generates a call to __mulsi3, multiplying r25:22 by r21:18
>  > and returning the result in r25:22.
>  >
>  > However, I cannot find where r21:18 are set in the code.  Looking at the
>  > output of avr-gcc -S, I cannot find any of r18:21.
> 
> 
The compilable source is 3700 lines.  I can post it if necessary.

I think the following will demo the problem

1.  Create the two files, as below.
2.  Compile with
    avr-gcc  -mmcu=atmega32  -Wall -Wmissing-prototypes  -Os \
    -fno-strict-aliasing  range.c global_var.c -o range.elf
3.  avr-objdump -d range.elf

===== range.c =======================
#include <avr/io.h>        // port definitions
#include <inttypes.h>

extern volatile uint8_t range_new;
extern volatile uint8_t range_local;
extern volatile uint8_t range_count;
extern volatile uint8_t range_local_ovfl;
extern volatile uint8_t disp_range_count;
extern volatile uint8_t disp_range_ovfl;
extern volatile uint8_t range_ovfl;

int main() {
  while(1) {
        // if we have new range data, process it
        if (range_new == 1) {
          {
                uint32_t distance = range_local_ovfl<<8;
                distance += (uint32_t)range_count;
                distance = 2345*distance;
                distance = distance >> 16;
                range_local = (uint8_t)(distance - 4)&0xff;
          }
          disp_range_count = range_count;
          disp_range_ovfl = range_ovfl;
        }
        return 0;
  }
}


==== global_var.c ===================
#include <avr/io.h>        // port definitions
#include <inttypes.h>

volatile uint8_t range_new;
volatile uint8_t range_local;
volatile uint8_t range_count;
volatile uint8_t range_local_ovfl;
volatile uint8_t disp_range_count;
volatile uint8_t disp_range_ovfl;
volatile uint8_t range_ovfl;