bjoernager/rust
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Avoid GenFuture shim when compiling async constructs

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Previously, async constructs would be lowered to "normal" generators,
with an additional `from_generator` / `GenFuture` shim in between to
convert from `Generator` to `Future`.

The compiler will now special-case these generators internally so that
async constructs will *directly* implement `Future` without the need
to go through the `from_generator` / `GenFuture` shim.

The primary motivation for this change was hiding this implementation
detail in stack traces and debuginfo, but it can in theory also help
the optimizer as there is less abstractions to see through.
This commit is contained in:
Arpad Borsos 2022-11-18 22:56:22 +01:00
parent fd815a5091
commit 9f36f988ad
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GPG key ID: FC7BCA77824B3298
41 changed files with 459 additions and 211 deletions
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60
compiler/rustc_trait_selection/src/traits/select/confirmation.rs
View file

@ -23,10 +23,11 @@ use crate::traits::{
BuiltinDerivedObligation, ImplDerivedObligation, ImplDerivedObligationCause, ImplSource,
ImplSourceAutoImplData, ImplSourceBuiltinData, ImplSourceClosureData,
ImplSourceConstDestructData, ImplSourceDiscriminantKindData, ImplSourceFnPointerData,
ImplSourceGeneratorData, ImplSourceObjectData, ImplSourcePointeeData, ImplSourceTraitAliasData,
ImplSourceTraitUpcastingData, ImplSourceUserDefinedData, Normalized, ObjectCastObligation,
Obligation, ObligationCause, OutputTypeParameterMismatch, PredicateObligation, Selection,
SelectionError, TraitNotObjectSafe, TraitObligation, Unimplemented, VtblSegment,
ImplSourceFutureData, ImplSourceGeneratorData, ImplSourceObjectData, ImplSourcePointeeData,
ImplSourceTraitAliasData, ImplSourceTraitUpcastingData, ImplSourceUserDefinedData, Normalized,
ObjectCastObligation, Obligation, ObligationCause, OutputTypeParameterMismatch,
PredicateObligation, Selection, SelectionError, TraitNotObjectSafe, TraitObligation,
Unimplemented, VtblSegment,
};
use super::BuiltinImplConditions;
@ -89,6 +90,11 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
ImplSource::Generator(vtable_generator)
}
FutureCandidate => {
let vtable_future = self.confirm_future_candidate(obligation)?;
ImplSource::Future(vtable_future)
}
FnPointerCandidate { .. } => {
let data = self.confirm_fn_pointer_candidate(obligation)?;
ImplSource::FnPointer(data)
@ -685,7 +691,21 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
debug!(?obligation, ?generator_def_id, ?substs, "confirm_generator_candidate");
let trait_ref = self.generator_trait_ref_unnormalized(obligation, substs);
let gen_sig = substs.as_generator().poly_sig();
// (1) Feels icky to skip the binder here, but OTOH we know
// that the self-type is an generator type and hence is
// in fact unparameterized (or at least does not reference any
// regions bound in the obligation). Still probably some
// refactoring could make this nicer.
let trait_ref = super::util::generator_trait_ref_and_outputs(
self.tcx(),
obligation.predicate.def_id(),
obligation.predicate.skip_binder().self_ty(), // (1)
gen_sig,
)
.map_bound(|(trait_ref, ..)| trait_ref);
let nested = self.confirm_poly_trait_refs(obligation, trait_ref)?;
debug!(?trait_ref, ?nested, "generator candidate obligations");
@ -693,6 +713,36 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
Ok(ImplSourceGeneratorData { generator_def_id, substs, nested })
}
fn confirm_future_candidate(
&mut self,
obligation: &TraitObligation<'tcx>,
) -> Result<ImplSourceFutureData<'tcx, PredicateObligation<'tcx>>, SelectionError<'tcx>> {
// Okay to skip binder because the substs on generator types never
// touch bound regions, they just capture the in-scope
// type/region parameters.
let self_ty = self.infcx.shallow_resolve(obligation.self_ty().skip_binder());
let ty::Generator(generator_def_id, substs, _) = *self_ty.kind() else {
bug!("closure candidate for non-closure {:?}", obligation);
};
debug!(?obligation, ?generator_def_id, ?substs, "confirm_future_candidate");
let gen_sig = substs.as_generator().poly_sig();
let trait_ref = super::util::future_trait_ref_and_outputs(
self.tcx(),
obligation.predicate.def_id(),
obligation.predicate.no_bound_vars().expect("future has no bound vars").self_ty(),
gen_sig,
)
.map_bound(|(trait_ref, ..)| trait_ref);
let nested = self.confirm_poly_trait_refs(obligation, trait_ref)?;
debug!(?trait_ref, ?nested, "future candidate obligations");
Ok(ImplSourceFutureData { generator_def_id, substs, nested })
}
#[instrument(skip(self), level = "debug")]
fn confirm_closure_candidate(
&mut self,