Try this snippet with various assembler versions, and watch the console output:
include \masm32\include\masm32rt.inc
.686
.xmm
showx MACRO arg
tmp$ CATSTR <Myarg=>, <arg>
% echo tmp$
ENDM
.code
start:
showx xmm1
showx Xmm1
showx XMM1
echo xmm1
% echo xmm1
echo XMM1
% echo XMM1
.err
exit
end start
Here is what I get:
6.14, 6.15:
Myarg=XMM(1)
Myarg=XMM(1)
Myarg=XMM(1)
xmm1
XMM(1)
XMM1
XMM(1)
9.0, JWasm:
Myarg=xmm1
Myarg=Xmm1
Myarg=XMM1
xmm1
xmm1
XMM1
XMM1
My suspicion is that the earlier Masm versions use equates and macros for working with xmm registers.