[avr-gcc-list] Endless loop: uchar c; for (c=1; c; c++)

[Dmitry K.]

Hi,

wrong code by avr-gcc 4.1.1:

Program:
~~~~~~~

/* This program is compiled as endless loop: condition `c1 != 0'
   is not tested.  In original (real) program there was an another
   error: in conditional expression based on c1 and c2 inside the
   loops (here this is removed).

   Compiler: avr-gcc 4.1.1
   Options: -W -Wall -Os -S     */

void foo (const char *s1, const char *s2);

int main ()
{
    unsigned char c1, c2;
    char s1[2] = ".";
    char s2[2] = ".";

    for (c1 = 1; c1; c1++) {
        for (c2 = 1; c2; c2++) {
            s1[0] = c1;
            s2[0] = c2;
            foo (s1, s2);
        }
    }
    return 0;
}

Result:
~~~~~~
        ...
main:
/* prologue: frame size=4 */
        ldi r28,lo8(__stack - 4)
        ldi r29,hi8(__stack - 4)
        out __SP_H__,r29
        out __SP_L__,r28
/* prologue end (size=4) */
        lds r24,.LC0
        lds r25,(.LC0)+1
        std Y+2,r25
        std Y+1,r24
        std Y+4,r25
        std Y+3,r24
        ldi r16,lo8(1)
        rjmp .L2
.L3:
        std Y+1,r16
        std Y+3,r17
        mov r22,r28
        mov r23,r29
        subi r22,lo8(-(3))
        sbci r23,hi8(-(3))
        mov r24,r28
        mov r25,r29
        adiw r24,1
        rcall foo
        subi r17,lo8(-(1))
        brne .L3
        subi r16,lo8(-(1))
.L2:
        ldi r17,lo8(1)
        rjmp .L3
/* epilogue: frame size=4 */
/* epilogue: noreturn */

Dmitry.