svn commit: r1639 - in trunk/yasm/modules/arch/x86: .

[peter at tortall.net]

Author: peter
Date: Tue Oct  3 21:38:43 2006
New Revision: 1639

Modified:
   trunk/yasm/modules/arch/x86/tests/xchg64.hex
   trunk/yasm/modules/arch/x86/x86id.c
Changeset:
   http://www.tortall.net/projects/yasm/changeset/1639

Log:
Follow-up to #80 and #81: "xchg ax, ax" can use the short 0x90 form as
16-bit operations don't clear the high bits of the 64-bit register, so
this is effectively a NOP as well.

While I'm still looking at this, make "xchg rax, rax" not output a REX
prefix.

I thought about being extra-clever and have "xchg ax, ax" not output an
operand-size prefix, but thought better of it: if the user says "ax"
they're probably going to expect the prefix to be there.  Left in as
a comment for future readers of the code.