[mypyc] Add experimental C extension librt.vecs (part 1/2) (#20653)
The extension defines the `vec[t]` type and associated functions. `vec`
is a sequence type optimized for use in compiled code. `vec` values are
immutable and represented internally as a struct with a length and
buffer fields. Only the buffer object is mutable. This allows very fast
access to the length field in compiled code, but any operations that
change the length of a `vec` value must return a modified `vec` value
(e.g. `append`).
Related issue: https://github.com/mypyc/mypyc/issues/840.
This PR doesn't define any mypyc primitives -- only use via generic
Python operations is supported at this point. I have a local branch that
implements efficient mypyc primitives for vecs, and there are
significant performance gains over `list` objects in benchmarks.
This PR only adds support for item types `i64`, `i32`, `i16`, `u8`,
`float` and `bool` (e.g. `vec[i32]`). A follow-up PR will add support
for reference item types (e.g. `vec[str]`) and nested vecs.
See the comment at the top of `mypyc/lib-rt/vecs/librt_vecs.c` for a
more detailed description. It also documents some implementation details
of reference item types and nested vec types (which are not included yet
in this PR).
Currently a fairly minimal API is supported. This example shows some of
the supported operations:
```
from librt.vecs import vec, append, remove, pop
v = vec[i32]([2, 3])
v[1] = v[0] + 2
v = append(v, 4)
v = remove(v, 2)
v, x = pop(v)
```
Additionally, read-only slicing and equality is supported. The `in`
operator and iteration only work through the sequence API, but I will
add proper support for these later on.
mypy
eabda0ee - [mypyc] Add experimental C extension librt.vecs (part 1/2) (#20653)
