Re: [avr-gcc-list] Need help compiling testcase with gcc 3.3.5 or 3.4.3

[Dmitry K.]

On Saturday 29 January 2005 00:30, Andy Hutchinson wrote:
> Thanks Ian!
>
> Ideally, loop should be transformed into 10..1 and end in BRNE or maybe
> 9..0 and BRLT.
>
> Here is difference
>
>         WINAVR 3.3.1        GCC4.0
> TESTLOOP1   9..0 loop       10..1 loop
>         SBRS            BRNE
>
> TESTLOOP2   0..9            9..0
>         cpi/cpc         SBRS
>
> TESTLOOP3   9..0            0..9
>         SBRS            cpi/cpc
>
> TESTLOOP4   0..9            9..0
>         cpi/cpc         SBRS
>
> TESTLOOP5   9..0            10..1
>         SBRS            BRNE

Another interesting case (-Os used):
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
int foo (int x)
{
    int i= x;
    do {
        x *= 2;
    } while (--i);
    return x;
}

Result with 3.3.4:
~~~~~~~~~~~~~~~~~~
foo:
/* prologue: frame size=0 */
/* prologue end (size=0) */
        mov r18,r24
        mov r19,r25
.L2:
        add r24,r24
        adc r25,r25
        subi r18,lo8(-(-1))
        sbci r19,hi8(-(-1))
        brne .L2
/* epilogue: frame size=0 */
        ret

Result with 4.0:
~~~~~~~~~~~~~~~~
foo:
/* prologue: frame size=0 */
/* prologue end (size=0) */
        ldi r18,lo8(0)
        ldi r19,hi8(0)
        clr r20
        clr r21
        sub r20,r24
        sbc r21,r25
.L2:
        add r24,r24
        adc r25,r25
        subi r18,lo8(-(-1))
        sbci r19,hi8(-(-1))
        cp r18,r20
        cpc r19,r21
        brne .L2
/* epilogue: frame size=0 */
        ret