Get rid of the per-value Vec in the LiveRange data type and use a
bforest::Map instead to represent the live-in intervals for non-local
live ranges.
This has some advantages:
- The memory footprint of a local live range is reduced from 40 to 20
bytes, and
- Clearing the Liveness data structure is now a constant time operation
which doesn't call free().
- The potentially quadratic behavior when computing large live ranges is
controlled by the logarithmic B-tree operations.
Rename the ArgumentType type to AbiParam since it describes the ABI
characteristics of a parameter or return value, not just the value type.
In Signature, rename members argument_types and return_types to "params"
and "returns". Again, they are not just types.
Fix a couple lingering references to "EBB arguments".
This is a verification pass that can be run after register allocation.
It verifies that value locations are consistent with constraints on
their uses, and that the register diversions are consistent.
Make it clear that register diversions are local to an EBB only. This
affects what branch relaxation is allowed to do.
The verify_locations() takes an optional Liveness parameter which is
used to check that no diverted values are live across CFG edges.
