This might not be a good idea, the problem was that
many spurious registers would be added to the Bits
data-structures during compilation (and would
always remain 0). However, doing the above
modification de-uniformizes the handling of temps
and regs, this makes the code longer and not
really nicer. Also, additional Bits structures
are required to track the registers independently.
Overall this might be a bad idea to revert.
The commutativity information only makes sense for
arithmetic expressions. To account for that, I introduced
a new tri-valued boolean type B3. Memory operations, for
example, will receive an undefined commutativity trit.
The code emitter was buggy when rega emitted instructions
like 'rax = add 1, rax', this is now fixed using the
commutativity information (we rewrite it in 'rax = add
rax, 1').
It seems that this logic of shuffling stuff around
between blocks should be handled by the register
allocator instead: it *will* have to shuffle
between registers, so we might as well mix some
spill locations in.
