When something calls `IdString::c_str()` on an autoidx ID, we need to cache the
full string in a thread-safe way. If we need to allocate an entry in some data
structure to do that, it's difficult to do in a thread-safe no-performance-hazard way.
So instead, store the cached string pointer in the same hashtable as the prefix
pointer.
We could make it safe to increment autoidx during multithreaded passes, but that's
actually undesirable because it would lead to nondeterminism. If/when we need new
IDs during parallel passes, we'll have to figure out how to allocate them in a
deterministic way, and that will depend on the details of what the pass does.
So don't try to tackle that now.
Refcounting is hardly used at all so this option is not that useful.
We might want to have a different option that disables GC if that becomes
a performance issue, but that should be a different option.
This saves space and doesn't cost very much since we hardly ever have nonzero refcounts any more.
It also allows for IdStrings with negative indexes, which we're going to add.
- consistently use value semantics for objects passed along FFI boundary
(not ideal but matches previous behavior)
- add new overload of RTLIL::Module: addMemory that does not require a "donor" object
- the idea is `Module`, `Memory`, `Wire`, `Cell` and `Process` cannot be directly constructed in Python and can only be added to the existing memory hierarchy in `Design` using the `add` methods - `Memory` requiring a donor object was the odd one out here
- fix superclass member wrapping only looking at direct superclass for inheritance instead of recursively checking superclasses
- fix superclass member wrapping not using superclass's denylists
- fix Design's `__str__` function not returning a string
- fix the generator crashing if there's any `std::function` in a header
- misc: add a crude `__repr__` based on `__str__`
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.
