x86: Update memcpy/memset inline strategies for Skylake family CPUs
Simply memcpy and memset inline strategies to avoid branches for
Skylake family CPUs:
1. With MOVE_RATIO and CLEAR_RATIO == 17, GCC will use integer/vector
load and store for up to 16 * 16 (256) bytes when the data size is
fixed and known.
2. Inline only if data size is known to be <= 256.
a. Use "rep movsb/stosb" with simple code sequence if the data size
is a constant.
b. Use loop if data size is not a constant.
3. Use memcpy/memset libray function if data size is unknown or > 256.
On Cascadelake processor with -march=native -Ofast -flto,