qemu/block/qcow2.c:1942: possible performance problem ?

I just ran static analyser cppcheck over today (20140520) qemu source code.

It said many things, including

[qemu/block/qcow2.c:1942] -> [qemu/block/qcow2.c:1943]: (performance) Buffer 'pad_buf' is being writ
ten before its old content has been used.

Source code is

            memset(pad_buf, 0, s->cluster_size);
            memcpy(pad_buf, buf, nb_sectors * BDRV_SECTOR_SIZE);

Worth tuning ?

Similar problem here

[qemu/block/qcow.c:815] -> [qemu/block/qcow.c:816]: (performance) Buffer 'pad_buf' is being written 
before its old content has been used.

and

[qemu/hw/i386/acpi-build.c:1265] -> [qemu/hw/i386/acpi-build.c:1267]: (performance) Buffer 'dsdt' is
 being written before its old content has been used.