edge splitting can cause new basic blocks to be added to the graph, but while
the graph itself gets properly rewritten the descriptor tables can't be updated
to take these into account, so they end up pointing at the wrong blocks. This
causes really hard-to-debug problems.
The new approach is to parse the descriptor blocks and then generate a
comparison chain. Brute force, but much easier for the compiler to reason
about.
need flt_arith any more. (And also generates them correctly on little-endian
systems.) as now parses numbers properly, doesn't trash memory all over the
place, and can handle negative numbers.
