TDA4VM: LLVM r5 C library memset/memcpy too slow ?

Hi experts,
I am using tda4vm sdk8.1, and I try to set no cached memory region (64M) to zero by c library memset function on mcu3_0,
but it consume about 14 second.

I use mem_set8_arm function to replace memset as follow , it consume about 500ms.

static void *mem_set8_arm (void *dest, int c, size_t n)
{
    uint32_t *d = dest;
    uint8_t *dc = dest;
    uint32_t setflag32 =
        (c & 0xff) |
        ((c << 8) & 0xff00) |
        ((c << 16) & 0xff0000) |
        ((c << 24) & 0xff000000);
    uint8_t setflag8 = c & 0xff;

    while (n >= 64) {
        __asm __volatile
        (
            "\n\t mov r4, %[flag]"
            "\n\t mov r5, r4"
            "\n\t mov r6, r4"
            "\n\t mov r7, r4"
            "\n\t stmia %[dst]!,{r4-r7}"
            "\n\t stmia %[dst]!,{r4-r7}"
        :: [dst] "r" (d), [flag] "r" (&setflag32) : "r4", "r4", "r6", "r7");

        d += 16;

        n -= 64;
    }

    while (n >= 4) {
        *d++ = setflag32;
        n -= 4;
    }

    dc = (uint8_t *) d;

    while (n--)
        *dc++ = setflag8;

    return dest;
}

Regards,

Li quan