This adds a tier-up mechanism at loop edges, making it so we can
seamlessly (ish) transition between interpreted and native code so we
can start running wasm code immediately after validation while
compilation happens in the background, and switching to native code
eventually once we hit a big enough function that would benefit from
being compiled to begin with.
By default, `rustfmt` persists the import granularity. In practice, most
Rust code has import granularity "Module" due to LSP's actions.
"Item" gets rid of import groupings and achieves cleaner diffs and
better conflict resolution. Better greppability is a positive side
effect.
Note: it's an unstable rustfmt feature. `cargo +nightly fmt` must be
used instead of `cargo fmt`.
Wasm opcodes only need one byte plus a 24-bit selector for
prefixed instructions. Store them in u32 instead of u64 and reject
selectors that would not fit. Update the Rust opcode generator to
accept the new integer suffixes used by Opcode.h.
macOS POSIX shared memory objects returned by shm_open() only support
mmap() and ftruncate(). Calls to read(), write(), pread() or pwrite()
all fail with ESPIPE. The cranelift-compiler child was using pread/
pwrite via File::read_exact_at/write_all_at, which works fine on
Linux where the parent uses memfd_create(), but fails on macOS where
the parent uses shm_open().
Add a macOS-specific path that mmaps the inherited shm fd with
MAP_SHARED, mirroring the Windows MapViewOfFile path. Writes through
the mapping are automatically visible to the parent, so the explicit
write-back step at the end is also skipped on macOS.
