Curiously enough, using separate reads and writes, with appropriate nop padding, seems to do better than any read-modify-write variation I tried. By the way, r

Curiously enough, using separate reads and writes, with appropriate nop padding, seems to do better than any read-modify-write variation I tried. By the way, read-modify-write is not fused altogether: only the write part is fused, so it generates 2 unfused uops (read, add), plus the fused uop for the write + address generation. EDIT: Intel's compiler also generates read-modify-write code, but it ends up being slower than both gcc and clang.