[Bug c/21671] New: Returning result of long long multiply from function clobbers lower 32 bits

[j33433 at gmail dot com]

m68k-unknown-elf-gcc (GCC) 3.4.4

Bug: long long multiply is broken when returning the result from a
subroutine. When using -O3 or higher, the lower half of the 64 bit
result is set to zero. This example works correctly with -O2.

Do not compile ll.c and ll_test.c as one file. Test case 2
fails (2LL * 2LL), the variable 'res' is zero.

m68k-unknown-elf-gcc -Wall -mcpu32 -c -O3 ll.c

/*
 * ll.c
 */

long long
mul_ll (long long a, long long b)
{
    return a * b;
}

/*
 * ll_test.c
 */

long long mul_ll (long long a, long long b);

typedef struct
{
    long long a;
    long long b;
    long long result;
}
ll_test;

int
main (void)
{
    ll_test cases[] =
    {
        {
            1073741824LL, /* 2 ^ 30 */
            1000LL,
            1073741824000LL
        },
        {
            536870912LL,  /* 2 ^ 29 */
            2LL,
            1073741824LL,
        },
        {
            2LL,
            2LL,
            4LL,
        }
    };
    int i;
    long long res;

    for (i = 0; i < (sizeof (cases) / sizeof (cases[0])); i++)
    {
        res = mul_ll (cases[i].a, cases[i].b);

        if (res != cases[i].result)
        {
            printf ("case %d failed\n", i);
        }
    }

    return 0;
}

mul_ll:
        link.w %a6,#0
        movm.l #0x3f00,-(%sp)
        clr.l %d0
        clr.l %d1
        move.l 8(%a6),%d4
        move.l 12(%a6),%d5
        move.l 16(%a6),%d2
        move.l 20(%a6),%d3
        move.l %d5,%d7
        mulu.l %d3,%d0:%d7  *** %d7 should be %d1 ***
        move.l %d5,%d6
        muls.l %d2,%d6
        add.l %d0,%d6
        move.l %d3,%d2
        muls.l %d4,%d2
        move.l %d6,%d0
        add.l %d2,%d0
        movm.l (%sp)+,#0xfc
        unlk %a6
        rts

-- 
           Summary: Returning result of long long multiply from function
                    clobbers lower 32 bits
           Product: gcc
           Version: 3.4.4
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: j33433 at gmail dot com
                CC: gcc-bugs at gcc dot gnu dot org
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: m68k-unknown-elf


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21671