Add a optimization frameword for operand narrowing (where the operand
size doesn't matter beyond a certain range because only certain bits
are referenced.)
Add a macro *and* matching facility for dealing with segment selectors, which are
typically rm16/r32/r64, but exactly how that is applied varies
depending on if a datum is read or written.
Signed-off-by: H. Peter Anvin (Intel) <hpa@zytor.com>
49a56ea9ee