I've been septic since I introduced it, this commit
proves that it costs more than it helps. I've also fixed
a bad bug in rega() where I alloc'ed the wrong size for
internal arrays. Enums now have names so I can use them
to cast in gdb to get the name corresponding to a constant.
This new machine-independent mechanism might not be general
enough in the long term but, now, it provides a flexible way
to inform the spiller about the maximum number of arguments
of an instruction that can be spill locations.
There are two things I overlooked so far.
1. Binary instructions like cmp that do not have a result
in registers need the size suffix sometimes, for example
when comparing a spill location with a constant.
2. The register allocator needs to be adapted to support the
comparison instruction: it is not possible to compare two
spill locations without using a register.
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').
