[Bug c/56219] New: avr-gcc-4.7.2 missing __uint24 loop optimisation

[demiurg_spb at freemail dot ru]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56219



             Bug #: 56219

           Summary: avr-gcc-4.7.2 missing __uint24 loop optimisation

    Classification: Unclassified

           Product: gcc

           Version: 4.7.2

            Status: UNCONFIRMED

          Severity: normal

          Priority: P3

         Component: c

        AssignedTo: unassig...@gcc.gnu.org

        ReportedBy: demiurg_...@freemail.ru





int main(void)

{

//    static const unsigned long __flash br[8] = {0,}; // case1: 194 bytes

    static const __uint24      __flash br[8] = {0,}; // case2: 190 bytes

(should be case1 minus 8 bytes)



    unsigned char i=0;



    for (;;i++)

    {

        *((volatile unsigned char*)100) = br[i%8];

    }



    return (0);

}



//case1: avr-gcc-4.7.2 -S -mmcu=atmega8 -Os main.c

    ldi r24,0

.L2:

    mov r30,r24

    andi r30,lo8(7)

    ldi r25,lo8(4)

    mul r30,r25

    movw r30,r0

    clr __zero_reg__

    subi r30,lo8(-(br.1322))

    sbci r31,hi8(-(br.1322))

    lpm r25,Z

    sts 100,r25

    subi r24,lo8(-(1))

    rjmp .L2



//case2: avr-gcc-4.7.2 -S -mmcu=atmega8 -Os main.c

    ldi r18,0

.L2:

    mov r24,r18

    andi r24,lo8(7)

    ldi r25,0

    movw r30,r24

    lsl r30

    rol r31

    add r30,r24

    adc r31,r25

    subi r30,lo8(-(br.1322))

    sbci r31,hi8(-(br.1322))

    lpm r24,Z

    sts 100,r24

    subi r18,lo8(-(1))

    rjmp .L2