You'll likely see memcpy implemented using the vector extension, e.g.: memcpy: mv a3, a0 # Copy destination loop: vsetvli t0, a2, e8, m8,

You'll likely see memcpy implemented using the vector extension, e.g.: memcpy: mv a3, a0 # Copy destination loop: vsetvli t0, a2, e8, m8, ta, ma # Vectors of 8b vle8.v v0, (a1) # Load bytes add a1, a1, t0 # Bump pointer sub a2, a2, t0 # Decrement count vse8.v v0, (a3) # Store bytes add a3, a3, t0 # Bump pointer bnez a2, loop # Any more? ret # Return Are you sure `rep stos/movs` are actually optimal on x86_64 systems? Edit: I just ran tinymembench on my CPU (Ryzen 5 1600X) C copy backwards : 7300.7 MB/s (1.2%) C copy backwards (32 byte blocks) : 7330.5 MB/s (1.5%) C copy backwards (64 byte blocks) : 7313.6 MB/s (0.7%) C copy : 7385.3 MB/s (1.0%) C copy prefetched (32 bytes step) : 7737.9 MB/s (1.0%) C copy prefetched (64 bytes step) : 7701.1 MB/s (1.6%) C 2-pass copy : 6414.2 MB/s (2.1%) C 2-pass copy prefetched (32 bytes step) : 6947.9 MB/s (1.4%) C 2-pass copy prefetched (64 bytes step) : 6985.8 MB/s (1.5%) C fill : 9197.2 MB/s (1.2%) C fill (shuffle within 16 byte blocks) : 9193.0 MB/s (1.4%) C fill (shuffle within 32 byte blocks) : 9175.0 MB/s (2.2%) C fill (shuffle within 64 byte blocks) : 9229.0 MB/s (1.1%) --- standard memcpy : 11302.6 MB/s (1.2%) standard memset : 11046.1 MB/s (1.4%) --- MOVSB copy : 7668.6 MB/s (1.5%) MOVSD copy : 7607.0 MB/s (0.8%) SSE2 copy : 7987.0 MB/s (5.0%) SSE2 nontemporal copy : 11989.2 MB/s (2.7%) SSE2 copy prefetched (32 bytes step) : 7739.9 MB/s (1.3%) SSE2 copy prefetched (64 bytes step) : 7807.6 MB/s (2.9%) SSE2 nontemporal copy prefetched (32 bytes step) : 12503.7 MB/s (1.5%) SSE2 nontemporal copy prefetched (64 bytes step) : 12605.2 MB/s (2.5%) SSE2 2-pass copy : 6977.1 MB/s (1.7%) SSE2 2-pass copy prefetched (32 bytes step) : 7311.1 MB/s (1.8%) SSE2 2-pass copy prefetched (64 bytes step) : 7334.7 MB/s (1.5%) SSE2 2-pass nontemporal copy : 3223.3 MB/s SSE2 fill : 10919.1 MB/s (1.8%) SSE2 nontemporal fill : 30713.9 MB/s (1.8%)