base + index register addressing

[Michael P. Hayes]

Jeffrey A Law writes:
 >   > I was going to comment that the patch might be even better, if it
 >   > dealt with register + scaled register that some machines have (such
 >   > as the x86, ns32k, 88k to name the ones I've dealt with).
 > It's worth noting that patch only helps when the base/index is a hard reg,
 > which limits its usefulness on most of our platforms.  It's unclear if
 > the benefit for handling scaled register would outweigh the work involved.

Most of the utility of the patch occurs when an incoming function
argument is in a hard base (or possibly index) register.   

IMO, things would be simpler if two register addresses were
canonicalized so that the base register preceeded the index register,
i.e., (mem (plus (base_reg) (index_reg)).  This would reduce the
ambiguity when it comes to allocating base and index registers.

mph...