Now that they're no longer a RHash instance, we don't have to box the offsets, we can directly srore the raw values, and stop marking them.
RHash isn't a good fit for storing `cdhash` as this force to allow arbitrary hash types into RHash, which doesn't work with AR tables. It also cause the cdhash to be larger than needed.
The `too_` prefix wasn't consistently used and just make the thing longer for no benefit.
Now that we have 1024B slots, we can store up to 126 fields inline. Objects larger than this are rare if not non-existent, hence we can get rid of the `malloc` path for imemo/fields and simply transition to `TOO_COMPLEX`. This additionally allows to shrink `attr_index_t` from 16 to 8B. Note: the ZJIT "ivar on extended" tests are renamed as "complex" because "extended" AKA malloc allocated imemo/fields no longer exists. They're now complex fields, AKA st tables. rb_class_allocate_instance: start as complex when over max_fields If `RCLASS_MAX_IV_COUNT` is over `max_fields`, allocating a large slot to end up transitioning to `TOO_COMPLEX` is wasteful. We might as well start as complex directly.
By only storing shape offsets in the cache, we're able to still match two equal objects that happen to be in different heaps, as well as to validate the object is neither frozen nor complex.
Expose both `rb_obj_shape_` functions that take a `VALUE` and `rb_shape_` functions that take a `shape_id`. Make common transition functions such as `complex` and `frozen` inlineable. Also get rid of RB_SET_SHAPE_ID and rb_set_boxed_class_shape_id.
Extracted from: https://github.com/ruby/ruby/pull/16817 It's likely that it will be u8 soon.
Embed and shrink the capacities array so that it can be queried more efficiently. Move `next_shape_id` and `cache_size` outside of the struct on their own cache line, as they're expected to be incremented atomically from concurrent threads, so we want to avoid false sharing. The also don't need to be exposed to the rest of the VM. Get rid of `root_shape` as it's always equal to `shape_list`.
As the documentation puts it, transmute is "incredibly unsafe". We can express what we need to with pointer casts in these closure FFI situations, so let's use pointer casts.