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Transform async ResumeTy in generator transform

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- Eliminates all the `get_context` calls that async lowering created.
- Replace all `Local` `ResumeTy` types with `&mut Context<'_>`.

The `Local`s that have their types replaced are:
- The `resume` argument itself.
- The argument to `get_context`.
- The yielded value of a `yield`.

The `ResumeTy` hides a `&mut Context<'_>` behind an unsafe raw pointer, and the
`get_context` function is being used to convert that back to a `&mut Context<'_>`.

Ideally the async lowering would not use the `ResumeTy`/`get_context` indirection,
but rather directly use `&mut Context<'_>`, however that would currently
lead to higher-kinded lifetime errors.
See <https://github.com/rust-lang/rust/issues/105501>.

The async lowering step and the type / lifetime inference / checking are
still using the `ResumeTy` indirection for the time being, and that indirection
is removed here. After this transform, the generator body only knows about `&mut Context<'_>`.
This commit is contained in:
Arpad Borsos 2022-12-20 15:15:29 +01:00
parent 6ba6d22bdf
commit 96931a787a
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GPG key ID: FC7BCA77824B3298
10 changed files with 549 additions and 14 deletions
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34
compiler/rustc_ty_utils/src/abi.rs
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@ -108,21 +108,41 @@ fn fn_sig_for_fn_abi<'tcx>(
// `Generator::resume(...) -> GeneratorState` function in case we
// have an ordinary generator, or the `Future::poll(...) -> Poll`
// function in case this is a special generator backing an async construct.
let ret_ty = if tcx.generator_is_async(did) {
let state_did = tcx.require_lang_item(LangItem::Poll, None);
let state_adt_ref = tcx.adt_def(state_did);
let state_substs = tcx.intern_substs(&[sig.return_ty.into()]);
tcx.mk_adt(state_adt_ref, state_substs)
let (resume_ty, ret_ty) = if tcx.generator_is_async(did) {
// The signature should be `Future::poll(_, &mut Context<'_>) -> Poll<Output>`
let poll_did = tcx.require_lang_item(LangItem::Poll, None);
let poll_adt_ref = tcx.adt_def(poll_did);
let poll_substs = tcx.intern_substs(&[sig.return_ty.into()]);
let ret_ty = tcx.mk_adt(poll_adt_ref, poll_substs);
// We have to replace the `ResumeTy` that is used for type and borrow checking
// with `&mut Context<'_>` which is used in codegen.
#[cfg(debug_assertions)]
{
if let ty::Adt(resume_ty_adt, _) = sig.resume_ty.kind() {
let expected_adt =
tcx.adt_def(tcx.require_lang_item(LangItem::ResumeTy, None));
assert_eq!(*resume_ty_adt, expected_adt);
} else {
panic!("expected `ResumeTy`, found `{:?}`", sig.resume_ty);
};
}
let context_mut_ref = tcx.mk_task_context();
(context_mut_ref, ret_ty)
} else {
// The signature should be `Generator::resume(_, Resume) -> GeneratorState<Yield, Return>`
let state_did = tcx.require_lang_item(LangItem::GeneratorState, None);
let state_adt_ref = tcx.adt_def(state_did);
let state_substs = tcx.intern_substs(&[sig.yield_ty.into(), sig.return_ty.into()]);
tcx.mk_adt(state_adt_ref, state_substs)
let ret_ty = tcx.mk_adt(state_adt_ref, state_substs);
(sig.resume_ty, ret_ty)
};
ty::Binder::bind_with_vars(
tcx.mk_fn_sig(
[env_ty, sig.resume_ty].iter(),
[env_ty, resume_ty].iter(),
&ret_ty,
false,
hir::Unsafety::Normal,