This commit adds a test harness and the beginnings of a test suite for
the crate that performs GC over a wasm module. This crate historically
has had zero tests because it was thought that it would no longer be
used once LLD landed with `--gc-sections`, but `wasm-bindgen` has come
to rely more and more on `wasm-gc` for various purposes.
The last release of `wasm-bindgen` was also released with a bug in the
recently refactored support in the `wasm-gc` crate, providing a perfect
time and motivation to start writing some tests!
All tests added here are `*.wat` files which contain the expected output
after the gc pass is executed. Tests are automatically updated with
`BLESS_TESTS=1` in the environment, which is the expected way to
generate the output for each test.
This commit updates the `wasm-gc` pass of wasm-bindgen to eliminate
duplicate types in the type section, effectively enabling a gc of the
type section itself. The main purpose here is ensure that code generated
by `wasm-bindgen` itself doesn't have to go too far out of its way to
deduplicate at generation time, but rather it can rely on the gc pass to
clean up.
Note that this currently depends on paritytech/parity-wasm#231, but this
can be updated if that ends up not landing.
This commit adds support for running a gc pass over locals in a
function. This will remove dead local declarations for a function
(completely unused) as well as compact existing entries to ensure that
we don't have two local declarations of the same type.
While this was initially intended for some future support of emitting
shims in `wasm-bindgen`, it turns out this pass is firing quite a lot
over existing functions generated by LLVM. Looks like we may see benefit
from this today with slightly smaller wasm binaries!
These don't seem to be widely used and they're not needed by
wasm-bindgen itself, so let's remove the symbols by default and
optionally in the future we can add an option to retain them.
This commit restructures some of the internals of `wasm-gc` now that
I've actually got a better grasp on the wasm format and what all the
ownership edges look like. This shouldn't actually result in any
user-facing changes, but should make us be a bit more compatible with
operations in the future.
Memories/tables/elements/segments are no longer considered automatic
roots but rather need to be rooted by something else to prevent a gc.
For example an element section is gc'd along with a table if the table
is never referenced, along with data segments as well if the memory
isn't referenced.
Additionally all index sets now don't contained offseted indices, but
rather everything is always stored relative to the "index space" to
ensure consistency.
This should make it a bit easier to add future items to gc!
The `wasm-bindgen` crate is effectively the only user of this crate now
that the `wasm-gc` tool has been deprecated. It's also much easier to
keep it in this repository as it's easier to sync changes to
`parity-wasm`. I'd also like to start refactoring out utilities for
managing a `parity_wasm::Module` to share between this crate and the
other CLI support code.
