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Auto merge of #126505 - compiler-errors:no-vtable, r=lcnr

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Only compute vtable information during codegen

This PR removes vtable information from the `Object` and `TraitUpcasting` candidate sources in the trait solvers, and defers the computation of relevant information to `Instance::resolve`. This is because vtables really aren't a thing in the trait world -- they're an implementation detail in codegen.

Previously it was just easiest to tangle this information together since we were already doing the work of looking at all the supertraits in the trait solver, and specifically because we use traits to represent when it's possible to call a method via a vtable (`Object` candidate) and do upcasting (`Unsize` candidate). but I am somewhat suspicious we're doing a *lot* of extra work, especially in polymorphic contexts, so let's see what perf says.
This commit is contained in:
bors 2024-06-16 05:33:49 +00:00
commit 5639c21fb3
14 changed files with 141 additions and 195 deletions
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3
compiler/rustc_codegen_cranelift/src/unsize.rs
View File

@ -39,8 +39,7 @@ pub(crate) fn unsized_info<'tcx>(
}
// trait upcasting coercion
let vptr_entry_idx =
fx.tcx.vtable_trait_upcasting_coercion_new_vptr_slot((source, target));
let vptr_entry_idx = fx.tcx.supertrait_vtable_slot((source, target));
if let Some(entry_idx) = vptr_entry_idx {
let entry_idx = u32::try_from(entry_idx).unwrap();

3
compiler/rustc_codegen_ssa/src/base.rs
View File

@ -163,8 +163,7 @@ pub fn unsized_info<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
// trait upcasting coercion
let vptr_entry_idx =
cx.tcx().vtable_trait_upcasting_coercion_new_vptr_slot((source, target));
let vptr_entry_idx = cx.tcx().supertrait_vtable_slot((source, target));
if let Some(entry_idx) = vptr_entry_idx {
let ptr_size = bx.data_layout().pointer_size;

8
compiler/rustc_middle/src/query/keys.rs
View File

@ -360,6 +360,14 @@ impl<'tcx> Key for (ty::ParamEnv<'tcx>, ty::TraitRef<'tcx>) {
}
}
impl<'tcx> Key for ty::TraitRef<'tcx> {
type Cache<V> = DefaultCache<Self, V>;
fn default_span(&self, tcx: TyCtxt<'_>) -> Span {
tcx.def_span(self.def_id)
}
}
impl<'tcx> Key for ty::PolyTraitRef<'tcx> {
type Cache<V> = DefaultCache<Self, V>;

7
compiler/rustc_middle/src/query/mod.rs
View File

@ -46,6 +46,7 @@ use crate::traits::{
};
use crate::ty::fast_reject::SimplifiedType;
use crate::ty::layout::ValidityRequirement;
use crate::ty::print::PrintTraitRefExt;
use crate::ty::util::AlwaysRequiresDrop;
use crate::ty::TyCtxtFeed;
use crate::ty::{
@ -1271,7 +1272,11 @@ rustc_queries! {
desc { |tcx| "finding all vtable entries for trait `{}`", tcx.def_path_str(key.def_id()) }
}
query vtable_trait_upcasting_coercion_new_vptr_slot(key: (Ty<'tcx>, Ty<'tcx>)) -> Option<usize> {
query first_method_vtable_slot(key: ty::TraitRef<'tcx>) -> usize {
desc { |tcx| "finding the slot within the vtable of `{}` for the implementation of `{}`", key.self_ty(), key.print_only_trait_name() }
}
query supertrait_vtable_slot(key: (Ty<'tcx>, Ty<'tcx>)) -> Option<usize> {
desc { |tcx| "finding the slot within vtable for trait object `{}` vtable ptr during trait upcasting coercion from `{}` vtable",
key.1, key.0 }
}

9
compiler/rustc_trait_selection/src/solve/assembly/mod.rs
View File

@ -5,6 +5,7 @@ use rustc_hir::def_id::DefId;
use rustc_hir::LangItem;
use rustc_infer::infer::InferCtxt;
use rustc_infer::traits::query::NoSolution;
use rustc_infer::traits::util::supertraits;
use rustc_middle::bug;
use rustc_middle::traits::solve::inspect::ProbeKind;
use rustc_middle::traits::solve::{Certainty, Goal, MaybeCause, QueryResult};
@ -744,14 +745,14 @@ impl<'tcx> EvalCtxt<'_, InferCtxt<'tcx>> {
// a projection goal.
if let Some(principal) = bounds.principal() {
let principal_trait_ref = principal.with_self_ty(tcx, self_ty);
self.walk_vtable(principal_trait_ref, |ecx, assumption, vtable_base, _| {
for (idx, assumption) in supertraits(self.interner(), principal_trait_ref).enumerate() {
candidates.extend(G::probe_and_consider_object_bound_candidate(
ecx,
CandidateSource::BuiltinImpl(BuiltinImplSource::Object { vtable_base }),
self,
CandidateSource::BuiltinImpl(BuiltinImplSource::Object(idx)),
goal,
assumption.upcast(tcx),
));
});
}
}
}

36
compiler/rustc_trait_selection/src/solve/eval_ctxt/mod.rs
View File

@ -24,7 +24,6 @@ use rustc_type_ir_macros::{Lift_Generic, TypeFoldable_Generic, TypeVisitable_Gen
use std::ops::ControlFlow;
use crate::traits::coherence;
use crate::traits::vtable::{count_own_vtable_entries, prepare_vtable_segments, VtblSegment};
use super::inspect::ProofTreeBuilder;
use super::{search_graph, GoalEvaluationKind, FIXPOINT_STEP_LIMIT};
@ -1022,41 +1021,6 @@ impl<'tcx> EvalCtxt<'_, InferCtxt<'tcx>> {
}
}
}
/// Walk through the vtable of a principal trait ref, executing a `supertrait_visitor`
/// for every trait ref encountered (including the principal). Passes both the vtable
/// base and the (optional) vptr slot.
pub(super) fn walk_vtable(
&mut self,
principal: ty::PolyTraitRef<'tcx>,
mut supertrait_visitor: impl FnMut(&mut Self, ty::PolyTraitRef<'tcx>, usize, Option<usize>),
) {
let tcx = self.interner();
let mut offset = 0;
prepare_vtable_segments::<()>(tcx, principal, |segment| {
match segment {
VtblSegment::MetadataDSA => {
offset += TyCtxt::COMMON_VTABLE_ENTRIES.len();
}
VtblSegment::TraitOwnEntries { trait_ref, emit_vptr } => {
let own_vtable_entries = count_own_vtable_entries(tcx, trait_ref);
supertrait_visitor(
self,
trait_ref,
offset,
emit_vptr.then(|| offset + own_vtable_entries),
);
offset += own_vtable_entries;
if emit_vptr {
offset += 1;
}
}
}
ControlFlow::Continue(())
});
}
}
/// Eagerly replace aliases with inference variables, emitting `AliasRelate`

4
compiler/rustc_trait_selection/src/solve/eval_ctxt/select.rs
View File

@ -114,8 +114,8 @@ fn candidate_should_be_dropped_in_favor_of<'tcx>(
// In the old trait solver, we arbitrarily choose lower vtable candidates
// over higher ones.
(
CandidateSource::BuiltinImpl(BuiltinImplSource::Object { vtable_base: a }),
CandidateSource::BuiltinImpl(BuiltinImplSource::Object { vtable_base: b }),
CandidateSource::BuiltinImpl(BuiltinImplSource::Object(a)),
CandidateSource::BuiltinImpl(BuiltinImplSource::Object(b)),
) => a >= b,
// Prefer dyn candidates over non-dyn candidates. This is necessary to
// handle the unsoundness between `impl<T: ?Sized> Any for T` and `dyn Any: Any`.

32
compiler/rustc_trait_selection/src/solve/trait_goals.rs
View File

@ -9,6 +9,7 @@ use rustc_hir::{LangItem, Movability};
use rustc_infer::infer::InferCtxt;
use rustc_infer::traits::query::NoSolution;
use rustc_infer::traits::solve::MaybeCause;
use rustc_infer::traits::util::supertraits;
use rustc_middle::bug;
use rustc_middle::traits::solve::inspect::ProbeKind;
use rustc_middle::traits::solve::{CandidateSource, Certainty, Goal, QueryResult};
@ -756,24 +757,19 @@ impl<'tcx> EvalCtxt<'_, InferCtxt<'tcx>> {
a_data.principal(),
));
} else if let Some(a_principal) = a_data.principal() {
self.walk_vtable(
a_principal.with_self_ty(tcx, a_ty),
|ecx, new_a_principal, _, vtable_vptr_slot| {
responses.extend(ecx.consider_builtin_upcast_to_principal(
goal,
CandidateSource::BuiltinImpl(BuiltinImplSource::TraitUpcasting {
vtable_vptr_slot,
}),
a_data,
a_region,
b_data,
b_region,
Some(new_a_principal.map_bound(|trait_ref| {
ty::ExistentialTraitRef::erase_self_ty(tcx, trait_ref)
})),
));
},
);
for new_a_principal in supertraits(tcx, a_principal.with_self_ty(tcx, a_ty)).skip(1) {
responses.extend(self.consider_builtin_upcast_to_principal(
goal,
CandidateSource::BuiltinImpl(BuiltinImplSource::TraitUpcasting),
a_data,
a_region,
b_data,
b_region,
Some(new_a_principal.map_bound(|trait_ref| {
ty::ExistentialTraitRef::erase_self_ty(tcx, trait_ref)
})),
));
}
}
responses

2
compiler/rustc_trait_selection/src/traits/mod.rs
View File

@ -65,7 +65,7 @@ pub use self::structural_match::search_for_structural_match_violation;
pub use self::structural_normalize::StructurallyNormalizeExt;
pub use self::util::elaborate;
pub use self::util::{expand_trait_aliases, TraitAliasExpander, TraitAliasExpansionInfo};
pub use self::util::{get_vtable_index_of_object_method, impl_item_is_final, upcast_choices};
pub use self::util::{impl_item_is_final, upcast_choices};
pub use self::util::{supertraits, transitive_bounds, transitive_bounds_that_define_assoc_item};
pub use self::util::{with_replaced_escaping_bound_vars, BoundVarReplacer, PlaceholderReplacer};

43
compiler/rustc_trait_selection/src/traits/select/confirmation.rs
View File

@ -22,10 +22,6 @@ use rustc_span::def_id::DefId;
use crate::traits::normalize::{normalize_with_depth, normalize_with_depth_to};
use crate::traits::util::{self, closure_trait_ref_and_return_type};
use crate::traits::vtable::{
count_own_vtable_entries, prepare_vtable_segments, vtable_trait_first_method_offset,
VtblSegment,
};
use crate::traits::{
ImplDerivedCause, ImplSource, ImplSourceUserDefinedData, Normalized, Obligation,
ObligationCause, PolyTraitObligation, PredicateObligation, Selection, SelectionError,
@ -689,13 +685,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
debug!(?nested, "object nested obligations");
let vtable_base = vtable_trait_first_method_offset(
tcx,
unnormalized_upcast_trait_ref,
ty::Binder::dummy(object_trait_ref),
);
Ok(ImplSource::Builtin(BuiltinImplSource::Object { vtable_base: vtable_base }, nested))
Ok(ImplSource::Builtin(BuiltinImplSource::Object(index), nested))
}
fn confirm_fn_pointer_candidate(
@ -1125,36 +1115,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
)?
.expect("did not expect ambiguity during confirmation");
let vtable_segment_callback = {
let mut vptr_offset = 0;
move |segment| {
match segment {
VtblSegment::MetadataDSA => {
vptr_offset += TyCtxt::COMMON_VTABLE_ENTRIES.len();
}
VtblSegment::TraitOwnEntries { trait_ref, emit_vptr } => {
vptr_offset += count_own_vtable_entries(tcx, trait_ref);
if trait_ref == unnormalized_upcast_principal {
if emit_vptr {
return ControlFlow::Break(Some(vptr_offset));
} else {
return ControlFlow::Break(None);
}
}
if emit_vptr {
vptr_offset += 1;
}
}
}
ControlFlow::Continue(())
}
};
let vtable_vptr_slot =
prepare_vtable_segments(tcx, source_principal, vtable_segment_callback).unwrap();
Ok(ImplSource::Builtin(BuiltinImplSource::TraitUpcasting { vtable_vptr_slot }, nested))
Ok(ImplSource::Builtin(BuiltinImplSource::TraitUpcasting, nested))
}
fn confirm_builtin_unsize_candidate(

17
compiler/rustc_trait_selection/src/traits/util.rs
View File

@ -208,23 +208,6 @@ pub fn upcast_choices<'tcx>(
supertraits(tcx, source_trait_ref).filter(|r| r.def_id() == target_trait_def_id).collect()
}
/// Given an upcast trait object described by `object`, returns the
/// index of the method `method_def_id` (which should be part of
/// `object.upcast_trait_ref`) within the vtable for `object`.
pub fn get_vtable_index_of_object_method<'tcx>(
tcx: TyCtxt<'tcx>,
vtable_base: usize,
method_def_id: DefId,
) -> Option<usize> {
// Count number of methods preceding the one we are selecting and
// add them to the total offset.
tcx.own_existential_vtable_entries(tcx.parent(method_def_id))
.iter()
.copied()
.position(|def_id| def_id == method_def_id)
.map(|index| vtable_base + index)
}
pub fn closure_trait_ref_and_return_type<'tcx>(
tcx: TyCtxt<'tcx>,
fn_trait_def_id: DefId,

127
compiler/rustc_trait_selection/src/traits/vtable.rs
View File

@ -1,15 +1,11 @@
use crate::errors::DumpVTableEntries;
use crate::traits::{impossible_predicates, is_vtable_safe_method};
use rustc_hir::def_id::DefId;
use rustc_hir::lang_items::LangItem;
use rustc_infer::traits::util::PredicateSet;
use rustc_infer::traits::ImplSource;
use rustc_middle::bug;
use rustc_middle::query::Providers;
use rustc_middle::traits::BuiltinImplSource;
use rustc_middle::ty::visit::TypeVisitableExt;
use rustc_middle::ty::GenericArgs;
use rustc_middle::ty::{self, GenericParamDefKind, Ty, TyCtxt, Upcast, VtblEntry};
use rustc_middle::ty::{GenericArgs, TypeVisitableExt};
use rustc_span::{sym, Span};
use smallvec::{smallvec, SmallVec};
@ -320,30 +316,42 @@ fn vtable_entries<'tcx>(
tcx.arena.alloc_from_iter(entries)
}
/// Find slot base for trait methods within vtable entries of another trait
pub(super) fn vtable_trait_first_method_offset<'tcx>(
tcx: TyCtxt<'tcx>,
trait_to_be_found: ty::PolyTraitRef<'tcx>,
trait_owning_vtable: ty::PolyTraitRef<'tcx>,
) -> usize {
// #90177
let trait_to_be_found_erased = tcx.erase_regions(trait_to_be_found);
// Given a `dyn Subtrait: Supertrait` trait ref, find corresponding first slot
// for `Supertrait`'s methods in the vtable of `Subtrait`.
pub(crate) fn first_method_vtable_slot<'tcx>(tcx: TyCtxt<'tcx>, key: ty::TraitRef<'tcx>) -> usize {
debug_assert!(!key.has_non_region_infer() && !key.has_non_region_param());
let ty::Dynamic(source, _, _) = *key.self_ty().kind() else {
bug!();
};
let source_principal = tcx
.normalize_erasing_regions(ty::ParamEnv::reveal_all(), source.principal().unwrap())
.with_self_ty(tcx, tcx.types.trait_object_dummy_self);
let target_principal = tcx
.normalize_erasing_regions(ty::ParamEnv::reveal_all(), key)
// We don't care about the self type, since it will always be the same thing.
.with_self_ty(tcx, tcx.types.trait_object_dummy_self);
let vtable_segment_callback = {
let mut vtable_base = 0;
let mut vptr_offset = 0;
move |segment| {
match segment {
VtblSegment::MetadataDSA => {
vtable_base += TyCtxt::COMMON_VTABLE_ENTRIES.len();
vptr_offset += TyCtxt::COMMON_VTABLE_ENTRIES.len();
}
VtblSegment::TraitOwnEntries { trait_ref, emit_vptr } => {
if tcx.erase_regions(trait_ref) == trait_to_be_found_erased {
return ControlFlow::Break(vtable_base);
if tcx
.normalize_erasing_late_bound_regions(ty::ParamEnv::reveal_all(), trait_ref)
== target_principal
{
return ControlFlow::Break(vptr_offset);
}
vtable_base += count_own_vtable_entries(tcx, trait_ref);
vptr_offset += tcx.own_existential_vtable_entries(trait_ref.def_id()).len();
if emit_vptr {
vtable_base += 1;
vptr_offset += 1;
}
}
}
@ -351,55 +359,72 @@ pub(super) fn vtable_trait_first_method_offset<'tcx>(
}
};
if let Some(vtable_base) =
prepare_vtable_segments(tcx, trait_owning_vtable, vtable_segment_callback)
{
vtable_base
} else {
bug!("Failed to find info for expected trait in vtable");
}
prepare_vtable_segments(tcx, source_principal, vtable_segment_callback).unwrap()
}
/// Find slot offset for trait vptr within vtable entries of another trait
pub(crate) fn vtable_trait_upcasting_coercion_new_vptr_slot<'tcx>(
/// Given a `dyn Subtrait` and `dyn Supertrait` trait object, find the slot of
/// // the trait vptr in the subtrait's vtable.
pub(crate) fn supertrait_vtable_slot<'tcx>(
tcx: TyCtxt<'tcx>,
key: (
Ty<'tcx>, // trait object type whose trait owning vtable
Ty<'tcx>, // trait object for supertrait
Ty<'tcx>, // Source -- `dyn Subtrait`.
Ty<'tcx>, // Target -- `dyn Supertrait` being coerced to.
),
) -> Option<usize> {
debug_assert!(!key.has_non_region_infer() && !key.has_non_region_param());
let (source, target) = key;
assert!(matches!(&source.kind(), &ty::Dynamic(..)) && !source.has_infer());
assert!(matches!(&target.kind(), &ty::Dynamic(..)) && !target.has_infer());
let ty::Dynamic(source, _, _) = *source.kind() else {
bug!();
};
let source_principal = tcx
.normalize_erasing_regions(ty::ParamEnv::reveal_all(), source.principal().unwrap())
.with_self_ty(tcx, tcx.types.trait_object_dummy_self);
// this has been typecked-before, so diagnostics is not really needed.
let unsize_trait_did = tcx.require_lang_item(LangItem::Unsize, None);
let ty::Dynamic(target, _, _) = *target.kind() else {
bug!();
};
let target_principal = tcx
.normalize_erasing_regions(ty::ParamEnv::reveal_all(), target.principal().unwrap())
.with_self_ty(tcx, tcx.types.trait_object_dummy_self);
let trait_ref = ty::TraitRef::new(tcx, unsize_trait_did, [source, target]);
let vtable_segment_callback = {
let mut vptr_offset = 0;
move |segment| {
match segment {
VtblSegment::MetadataDSA => {
vptr_offset += TyCtxt::COMMON_VTABLE_ENTRIES.len();
}
VtblSegment::TraitOwnEntries { trait_ref, emit_vptr } => {
vptr_offset += tcx.own_existential_vtable_entries(trait_ref.def_id()).len();
if tcx.normalize_erasing_regions(ty::ParamEnv::reveal_all(), trait_ref)
== target_principal
{
if emit_vptr {
return ControlFlow::Break(Some(vptr_offset));
} else {
return ControlFlow::Break(None);
}
}
match tcx.codegen_select_candidate((ty::ParamEnv::reveal_all(), trait_ref)) {
Ok(ImplSource::Builtin(BuiltinImplSource::TraitUpcasting { vtable_vptr_slot }, _)) => {
*vtable_vptr_slot
if emit_vptr {
vptr_offset += 1;
}
}
}
ControlFlow::Continue(())
}
otherwise => bug!("expected TraitUpcasting candidate, got {otherwise:?}"),
}
}
};
/// Given a trait `trait_ref`, returns the number of vtable entries
/// that come from `trait_ref`, excluding its supertraits. Used in
/// computing the vtable base for an upcast trait of a trait object.
pub(crate) fn count_own_vtable_entries<'tcx>(
tcx: TyCtxt<'tcx>,
trait_ref: ty::PolyTraitRef<'tcx>,
) -> usize {
tcx.own_existential_vtable_entries(trait_ref.def_id()).len()
prepare_vtable_segments(tcx, source_principal, vtable_segment_callback).unwrap()
}
pub(super) fn provide(providers: &mut Providers) {
*providers = Providers {
own_existential_vtable_entries,
vtable_entries,
vtable_trait_upcasting_coercion_new_vptr_slot,
first_method_vtable_slot,
supertrait_vtable_slot,
..*providers
};
}

22
compiler/rustc_ty_utils/src/instance.rs
View File

@ -213,13 +213,23 @@ fn resolve_associated_item<'tcx>(
Some(ty::Instance::new(leaf_def.item.def_id, args))
}
traits::ImplSource::Builtin(BuiltinImplSource::Object { vtable_base }, _) => {
traits::get_vtable_index_of_object_method(tcx, *vtable_base, trait_item_id).map(
|index| Instance {
def: ty::InstanceDef::Virtual(trait_item_id, index),
traits::ImplSource::Builtin(BuiltinImplSource::Object(_), _) => {
let trait_ref = ty::TraitRef::from_method(tcx, trait_id, rcvr_args);
if trait_ref.has_non_region_infer() || trait_ref.has_non_region_param() {
// We only resolve totally substituted vtable entries.
None
} else {
let vtable_base = tcx.first_method_vtable_slot(trait_ref);
let offset = tcx
.own_existential_vtable_entries(trait_id)
.iter()
.copied()
.position(|def_id| def_id == trait_item_id);
offset.map(|offset| Instance {
def: ty::InstanceDef::Virtual(trait_item_id, vtable_base + offset),
args: rcvr_args,
},
)
})
}
}
traits::ImplSource::Builtin(BuiltinImplSource::Misc, _) => {
if tcx.is_lang_item(trait_ref.def_id, LangItem::Clone) {

23
compiler/rustc_type_ir/src/solve.rs
View File

@ -171,25 +171,20 @@ pub enum CandidateSource<I: Interner> {
#[derive(Clone, Copy, Hash, PartialEq, Eq, Debug)]
#[cfg_attr(feature = "nightly", derive(HashStable_NoContext, TyEncodable, TyDecodable))]
pub enum BuiltinImplSource {
/// Some builtin impl we don't need to differentiate. This should be used
/// Some built-in impl we don't need to differentiate. This should be used
/// unless more specific information is necessary.
Misc,
/// A builtin impl for trait objects.
/// A built-in impl for trait objects. The index is only used in winnowing.
Object(usize),
/// A built-in implementation of `Upcast` for trait objects to other trait objects.
///
/// The vtable is formed by concatenating together the method lists of
/// the base object trait and all supertraits, pointers to supertrait vtable will
/// be provided when necessary; this is the start of `upcast_trait_ref`'s methods
/// in that vtable.
Object { vtable_base: usize },
/// The vtable is formed by concatenating together the method lists of
/// the base object trait and all supertraits, pointers to supertrait vtable will
/// be provided when necessary; this is the position of `upcast_trait_ref`'s vtable
/// within that vtable.
TraitUpcasting { vtable_vptr_slot: Option<usize> },
/// This can be removed when `feature(dyn_upcasting)` is stabilized, since we only
/// use it to detect when upcasting traits in hir typeck.
TraitUpcasting,
/// Unsizing a tuple like `(A, B, ..., X)` to `(A, B, ..., Y)` if `X` unsizes to `Y`.
///
/// This needs to be a separate variant as it is still unstable and we need to emit
/// a feature error when using it on stable.
/// This can be removed when `feature(tuple_unsizing)` is stabilized, since we only
/// use it to detect when unsizing tuples in hir typeck.
TupleUnsizing,
}