[avr-gcc-list] avr 32 bit math bug

[Shaun Jackman]

I've found two 32 bit math bugs in avr-gcc. Try the following code...
        uint32_t delay = 500000;
        while( --delay);
produces...
                delay = 500000;
  64:   80 e2           ldi     r24, 0x20       ; 32
  66:   91 ea           ldi     r25, 0xA1       ; 161
  68:   a7 e0           ldi     r26, 0x07       ; 7
  6a:   b0 e0           ldi     r27, 0x00       ; 0
                while( --delay);
  6c:   01 97           sbiw    r24, 0x01       ; 1
  6e:   a1 09           sbc     r26, r1
  70:   b1 09           sbc     r27, r1
  72:   e1 f7           brne    .-8             ; 0x6c
  74:   cc cf           rjmp    .-104           ; 0xe

There's two problems with this.
1. sbiw and sbc clear the zero flag, but they never set it!
2. r1 is used as a source register, but it's never initialized!

I had to work around it like this...
        uint32_t delay = 500000;
        asm( "clr r1");
        while( --delay)
                asm( "sez\n");
produces...
  12:   11 24           eor     r1, r1
                while( --delay)
  14:   8f e0           ldi     r24, 0x0F       ; 15
  16:   97 e2           ldi     r25, 0x27       ; 39
  18:   a0 e0           ldi     r26, 0x00       ; 0
  1a:   b0 e0           ldi     r27, 0x00       ; 0
                        asm( "sez\n");
  1c:   18 94           sez
  1e:   01 97           sbiw    r24, 0x01       ; 1
  20:   a1 09           sbc     r26, r1
  22:   b1 09           sbc     r27, r1
  24:   d9 f7           brne    .-10            ; 0x1c
  26:   f3 cf           rjmp    .-26            ; 0xe

Anyone seen this before?
avr-elf-gcc (GCC) 3.2 (Debian)
avr-elf-gcc -g -O2 -mmcu=at90s8515 foo.c -o foo

Thanks,
Shaun
avr-gcc-list at http://avr1.org