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Implement lowered-then-lifted functions (#4327)

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* Implement lowered-then-lifted functions

This commit is a few features bundled into one, culminating in the
implementation of lowered-then-lifted functions for the component model.
It's probably not going to be used all that often but this is possible
within a valid component so Wasmtime needs to do something relatively
reasonable. The main things implemented in this commit are:

* Component instances are now assigned a `RuntimeComponentInstanceIndex`
  to differentiate each one. This will be used in the future to detect
  fusion (one instance lowering a function from another instance). For
  now it's used to allocate separate `VMComponentFlags` for each
  internal component instance.

* The `CoreExport<FuncIndex>` of lowered functions was changed to a
  `CoreDef` since technically a lowered function can use another lowered
  function as the callee. This ended up being not too difficult to plumb
  through as everything else was already in place.

* A need arose to compile host-to-wasm trampolines which weren't already
  present. Currently wasm in a component is always entered through a
  host-to-wasm trampoline but core wasm modules are the source of all
  the trampolines. In the case of a lowered-then-lifted function there
  may not actually be any core wasm modules, so component objects now
  contain necessary trampolines not otherwise provided by the core wasm
  objects. This feature required splitting a new function into the
  `Compiler` trait for creating a host-to-wasm trampoline. After doing
  this core wasm compilation was also updated to leverage this which
  further enabled compiling trampolines in parallel as opposed to the
  previous synchronous compilation.

* Review comments
This commit is contained in:
Alex Crichton
2022-06-28 13:50:08 -05:00
committed by GitHub
parent df1502531d
commit c1b3962f7b
17 changed files with 400 additions and 107 deletions
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18
crates/environ/src/compilation.rs
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@@ -148,12 +148,21 @@ pub trait Compiler: Send + Sync {
types: &ModuleTypes,
) -> Result<Box<dyn Any + Send>, CompileError>;
/// Creates a function of type `VMTrampoline` which will then call the
/// function pointer argument which has the `ty` type provided.
fn compile_host_to_wasm_trampoline(
&self,
ty: &WasmFuncType,
) -> Result<Box<dyn Any + Send>, CompileError>;
/// Collects the results of compilation into an in-memory object.
///
/// This function will receive the same `Box<dyn Ayn>` produced as part of
/// `compile_function`, as well as the general compilation environment with
/// the translation/types. This method is expected to populate information
/// in the object file such as:
/// the translation. THe `trampolines` argument is generated by
/// `compile_host_to_wasm_trampoline` for each of
/// `module.exported_signatures`. This method is expected to populate
/// information in the object file such as:
///
/// * Compiled code in a `.text` section
/// * Unwind information in Wasmtime-specific sections
@@ -163,11 +172,14 @@ pub trait Compiler: Send + Sync {
///
/// The final result of compilation will contain more sections inserted by
/// the compiler-agnostic runtime.
///
/// This function returns information about the compiled functions (where
/// they are in the text section) along with where trampolines are located.
fn emit_obj(
&self,
module: &ModuleTranslation,
types: &ModuleTypes,
funcs: PrimaryMap<DefinedFuncIndex, Box<dyn Any + Send>>,
trampolines: Vec<Box<dyn Any + Send>>,
tunables: &Tunables,
obj: &mut Object<'static>,
) -> Result<(PrimaryMap<DefinedFuncIndex, FunctionInfo>, Vec<Trampoline>)>;