This can be done by passing
`--export-js <module>.<fn>[(<arg>:type, ...)][:type]=<source>`,
which uses a js function `(arg...) => source` to resolve the requested
import `module::fn`.
All literal wasm value types (i<n> and v128) are supported as both
parameter and return types.
This still passes the values on the stack, but registers are now allowed
to cross a call boundary.
This is a very significant (>50%) improvement on the small call
microbenchmarks on my machine.
This commit adds a register allocator, with 8 available "register"
slots.
In testing with various random blobs, this moves anywhere from 30% to
74% of value accesses into predefined slots, and is about a ~20% perf
increase end-to-end.
To actually make this usable, a few structural changes were also made:
- we no longer do one instruction per interpret call
- trapping is an (unlikely) exit condition
- the label and frame stacks are replaced with linked lists with a huge
node cache size, as we only need to touch the last element and
push/pop is very frequent.
This is largely unused (only in wasm.cpp)
A future reimplementation can bring it back as a separate interpreter
class that embeds the current bytecode interpreter.
...instead of specially handling JS::Completion.
This makes it possible for LibWeb/LibJS to have full control over how
these things are made, stored, and visited (whenever).
Fixes an issue where we couldn't roundtrip a JS exception through Wasm.
