Created by: khuey
xchg %ax,%r8w is separated from xchg %ax,%ax (aka OP_nop) only by REX.B. The decoding table was not reaching the 90 OP_xchg when coming through prefix_extensions.
Encoding of this short variant (and also e.g. xchg %eax, %r8d; xchg %eax, %r9d; etc) is still not handled, but those will fall back to the longer 87 xchg opcode.
Issue: #5442 (closed)