- Add a `simple_legalize()` function that invokes a predetermined set of
legalizations, without depending on the details of the current
backend design. This will be used by the new backend pipeline.
- Separate out `has_side_effect()` from the DCE pass. This will be used
by the new backends' lowering code.
- Add documentation for the `Arm64Call` relocation type.
This does a lot at once, since there was no clear way to split the three
commits:
- Instruction need to be passed an explicit InstructionFormat,
- InstructionFormat deduplication is checked once all entities have been
defined;
This follows the rest of the code base data structures, where we have a
mutable data structure builder; once the data structure is constructed,
it's immutable.
This also makes the definition of instructions easier, and it paves the
way for defining immediate variants.
