We were performing the helper passes `abc9_ops -replace_zbufs` and
`abc9_ops -restore_zbufs` for every module, but those passes act on the
full design (and can't be applied entirely selectively due to entering
and leaving bufnorm).
This lead to an explosive creation of a lot of redundant bufnorm helper
cells that would have been cleaned up by `clean` but that never ran.
Instead we now run each helper pass once, one before and one after
iterating over the selected modules. This limits the number of bufnorm
helper cells.
For consistency.
Also trying a new thing: only rebuilding objects that use the pybind11 library. The idea is these are the only objects that include the Python/pybind headers and thus the only ones that depend on the Python ABI in any capacity, so other objects can be reused across wheel builds. This has the potential to cut down build times.
- Rewrite all Python features to use the pybind11 library instead of boost::python.
Unlike boost::python, pybind11 is a header-only library that is just included by Pyosys code, saving a lot of compile time on wheels.
- Factor out as much "translation" code from the generator into proper C++ files
- Fix running the embedded interpreter not supporting "from pyosys import libyosys as ys" like wheels
- Move Python-related elements to `pyosys` directory at the root of the repo
- Slight shift in bridging semantics:
- Containers are declared as "opaque types" and are passed by reference to Python - many methods have been implemented to make them feel right at home without the overhead/ambiguity of copying to Python and then copying back after mutation
- Monitor/Pass use "trampoline" pattern to support virual methods overridable in Python: virtual methods no longer require `py_` prefix
- Create really short test set for pyosys that just exercises basic functionality
