1) there is no need to fiddle with IE, just the bit for the device that shares the variable.
2) in critical apps the following IS possible
dsbl int
nop
blah = shared int #1
enbl int
dsbl int
nop
bloh = shared int #2
enbl int
....

been there done that

I did, when doing the above 2) try many methods, but this one is 'clean' and works (the interrupt is only disabled for a very short time. I checked the generated assembler for "improvements of the C" and did switch to

U16 get_atomic1(void)

push IE
actual IE bit = 0
mov r6 intvar1
mov r7 intvar1+1
pop IE
ret

even with the function call it was faster

I then expanded to an array so 2) above became one function call to an asm routine.

Erik