is there any reason to handle the <asop> as single operations instead
of breaking it down into separate <as> and <op> operations? that is,
is (a <op>= b) always equivalent to (a = a <op> b)?
you then have to fuss whether the evaluation of a has side-effects, and
if so, add an assignment to a temporary. it turns out that the existing
code needs only a little more care about which type is used to allocate
registers, and on the RISCy machines it will then work. 8c is a little more
involved because of the 387's architecture. there probably won't be much code,
but it's fiddly. it would be nice finally to switch
to SSE but i suppose there might still be some SSE-less x86/32 processors.