Add a suggestion to consider deprecating opcodes 0x91 - 0x97.

These are a special case encoding of XCHG that hardcodes one register
as [E/R]AX and the other register is in the low 3 bits.  Encoding
the exchange using the existing 87 opcode is just one byte longer.

The deprecation would only be in capability mode.

Author: bsdjhb

chap-cheri-x86-64.tex

@@ -1434,3 +1434,9 @@ \subsection{Direct Memory-Offset MOVs}
 extended to support capability immediates for the memory offset.  In
 that case, the opcodes would be retained in capability mode rather
 than deprecated.
+
+\subsection{Single-byte XCHG Opcodes}
+
+If the single-byte \insnnoref{XCHG} instructions other than
+\insnnoref{NOP} (\texttt{90}) are not commonly used, they could be
+deprecated in capability mode.