[veddan]

Reasonably modern versions of GCC will emit various rep instructions in some cases.

Some code I just compiled with GCC 6.1.1 had several snippets like this emitted for zeroing with memset:

    xor eax,eax
    ...
    rep stos QWORD PTR es:[rdi],rax

and some rep movs for memcpy/memmove.

[chkras]

really? I wonder if the timing of rep and string instructions have improved at all?

[userbinator]

They operate on cacheline-sized pieces ever since the P6.