if self.0.has_escaping_bound_vars() { None } else { Some(self.skip_binder()) }
}
- pub fn no_bound_vars_ignoring_escaping(self, tcx: TyCtxt<'tcx>) -> Option<T>
- where
- T: TypeFoldable<'tcx>,
- {
- if !self.0.has_escaping_bound_vars() {
- Some(self.skip_binder())
- } else {
- self.0.try_fold_with(&mut SkipBindersAt { index: ty::INNERMOST, tcx }).ok()
- }
- }
-
/// Splits the contents into two things that share the same binder
/// level as the original, returning two distinct binders.
///
//! Code shared by trait and projection goals for candidate assembly.
use super::infcx_ext::InferCtxtExt;
-use super::{
- instantiate_canonical_query_response, CanonicalGoal, CanonicalResponse, Certainty, EvalCtxt,
- Goal,
-};
+use super::{CanonicalResponse, Certainty, EvalCtxt, Goal};
use rustc_hir::def_id::DefId;
-use rustc_infer::infer::TyCtxtInferExt;
-use rustc_infer::infer::{
- canonical::{CanonicalVarValues, OriginalQueryValues},
- InferCtxt,
-};
use rustc_infer::traits::query::NoSolution;
use rustc_middle::ty::TypeFoldable;
use rustc_middle::ty::{self, Ty, TyCtxt};
-use rustc_span::DUMMY_SP;
use std::fmt::Debug;
/// A candidate is a possible way to prove a goal.
fn trait_def_id(self, tcx: TyCtxt<'tcx>) -> DefId;
fn consider_impl_candidate(
- acx: &mut AssemblyCtxt<'_, 'tcx, Self>,
+ acx: &mut AssemblyCtxt<'_, '_, 'tcx, Self>,
goal: Goal<'tcx, Self>,
impl_def_id: DefId,
);
/// An abstraction which correctly deals with the canonical results for candidates.
///
/// It also deduplicates the behavior between trait and projection predicates.
-pub(super) struct AssemblyCtxt<'a, 'tcx, G: GoalKind<'tcx>> {
- pub(super) cx: &'a mut EvalCtxt<'tcx>,
- pub(super) infcx: &'a InferCtxt<'tcx>,
- var_values: CanonicalVarValues<'tcx>,
+pub(super) struct AssemblyCtxt<'a, 'b, 'tcx, G: GoalKind<'tcx>> {
+ pub(super) cx: &'a mut EvalCtxt<'b, 'tcx>,
candidates: Vec<Candidate<'tcx, G>>,
}
-impl<'a, 'tcx, G: GoalKind<'tcx>> AssemblyCtxt<'a, 'tcx, G> {
+impl<'a, 'b, 'tcx, G: GoalKind<'tcx>> AssemblyCtxt<'a, 'b, 'tcx, G> {
pub(super) fn assemble_and_evaluate_candidates(
- cx: &'a mut EvalCtxt<'tcx>,
- goal: CanonicalGoal<'tcx, G>,
+ cx: &'a mut EvalCtxt<'b, 'tcx>,
+ goal: Goal<'tcx, G>,
) -> Vec<Candidate<'tcx, G>> {
- let (ref infcx, goal, var_values) =
- cx.tcx.infer_ctxt().build_with_canonical(DUMMY_SP, &goal);
- let mut acx = AssemblyCtxt { cx, infcx, var_values, candidates: Vec::new() };
+ let mut acx = AssemblyCtxt { cx, candidates: Vec::new() };
acx.assemble_candidates_after_normalizing_self_ty(goal);
source: G::CandidateSource,
certainty: Certainty,
) {
- match self.infcx.make_canonical_response(self.var_values.clone(), certainty) {
+ match self.cx.make_canonical_response(certainty) {
Ok(result) => self.candidates.push(Candidate { source, result }),
Err(NoSolution) => debug!(?source, ?certainty, "failed leakcheck"),
}
/// self type to the list of candidates in case that succeeds. Note that we can't just eagerly return in
/// this case as projections as self types add `
fn assemble_candidates_after_normalizing_self_ty(&mut self, goal: Goal<'tcx, G>) {
- let tcx = self.cx.tcx;
+ let tcx = self.cx.tcx();
+ let infcx = self.cx.infcx;
// FIXME: We also have to normalize opaque types, not sure where to best fit that in.
let &ty::Alias(ty::Projection, projection_ty) = goal.predicate.self_ty().kind() else {
return
};
- self.infcx.probe(|_| {
- let normalized_ty = self.infcx.next_ty_infer();
+ infcx.probe(|_| {
+ let normalized_ty = infcx.next_ty_infer();
let normalizes_to_goal = goal.with(
tcx,
ty::Binder::dummy(ty::ProjectionPredicate {
term: normalized_ty.into(),
}),
);
- let normalization_certainty =
- match self.cx.evaluate_goal(&self.infcx, normalizes_to_goal) {
- Ok((_, certainty)) => certainty,
- Err(NoSolution) => return,
- };
+ let normalization_certainty = match self.cx.evaluate_goal(normalizes_to_goal) {
+ Ok((_, certainty)) => certainty,
+ Err(NoSolution) => return,
+ };
// NOTE: Alternatively we could call `evaluate_goal` here and only have a `Normalized` candidate.
// This doesn't work as long as we use `CandidateSource` in both winnowing and to resolve associated items.
let goal = goal.with(tcx, goal.predicate.with_self_ty(tcx, normalized_ty));
- let mut orig_values = OriginalQueryValues::default();
- let goal = self.infcx.canonicalize_query(goal, &mut orig_values);
let normalized_candidates =
AssemblyCtxt::assemble_and_evaluate_candidates(self.cx, goal);
-
- // Map each candidate from being canonical wrt the current inference context to being
- // canonical wrt the caller.
- for Candidate { source, result } in normalized_candidates {
- self.infcx.probe(|_| {
- let candidate_certainty =
- instantiate_canonical_query_response(&self.infcx, &orig_values, result);
-
- // FIXME: This is a bit scary if the `normalizes_to_goal` overflows.
- //
- // If we have an ambiguous candidate it hides that normalization
- // caused an overflow which may cause issues.
- self.try_insert_candidate(
- source,
- normalization_certainty.unify_and(candidate_certainty),
- )
- })
+ for mut normalized_candidate in normalized_candidates {
+ normalized_candidate.result =
+ normalized_candidate.result.unchecked_map(|mut response| {
+ response.certainty = response.certainty.unify_and(normalization_certainty);
+ response
+ });
+ self.candidates.push(normalized_candidate);
}
})
}
fn assemble_impl_candidates(&mut self, goal: Goal<'tcx, G>) {
- self.cx.tcx.for_each_relevant_impl(
- goal.predicate.trait_def_id(self.cx.tcx),
+ let tcx = self.cx.tcx();
+ tcx.for_each_relevant_impl(
+ goal.predicate.trait_def_id(tcx),
goal.predicate.self_ty(),
|impl_def_id| G::consider_impl_candidate(self, goal, impl_def_id),
);
+++ /dev/null
-//! This module both handles the global cache which stores "finished" goals,
-//! and the provisional cache which contains partially computed goals.
-//!
-//! The provisional cache is necessary when dealing with coinductive cycles.
-//!
-//! For more information about the provisional cache and coinduction in general,
-//! check out the relevant section of the rustc-dev-guide.
-//!
-//! FIXME(@lcnr): Write that section, feel free to ping me if you need help here
-//! before then or if I still haven't done that before January 2023.
-use super::overflow::OverflowData;
-use super::{CanonicalGoal, Certainty, MaybeCause, Response};
-use super::{EvalCtxt, QueryResult};
-use rustc_data_structures::fx::FxHashMap;
-use rustc_index::vec::IndexVec;
-use rustc_infer::infer::canonical::{Canonical, CanonicalVarKind, CanonicalVarValues};
-use rustc_middle::ty::{self, TyCtxt};
-use std::collections::hash_map::Entry;
-
-rustc_index::newtype_index! {
- pub struct StackDepth {}
-}
-rustc_index::newtype_index! {
- pub struct EntryIndex {}
-}
-
-#[derive(Debug, Clone)]
-struct ProvisionalEntry<'tcx> {
- // In case we have a coinductive cycle, this is the
- // the currently least restrictive result of this goal.
- response: QueryResult<'tcx>,
- // In case of a cycle, the depth of lowest stack entry involved
- // in that cycle. This is monotonically decreasing in the stack as all
- // elements between the current stack element in the lowest stack entry
- // involved have to also be involved in that cycle.
- //
- // We can only move entries to the global cache once we're complete done
- // with the cycle. If this entry has not been involved in a cycle,
- // this is just its own depth.
- depth: StackDepth,
-
- // The goal for this entry. Should always be equal to the corresponding goal
- // in the lookup table.
- goal: CanonicalGoal<'tcx>,
-}
-
-struct StackElem<'tcx> {
- goal: CanonicalGoal<'tcx>,
- has_been_used: bool,
-}
-
-pub(super) struct ProvisionalCache<'tcx> {
- stack: IndexVec<StackDepth, StackElem<'tcx>>,
- entries: IndexVec<EntryIndex, ProvisionalEntry<'tcx>>,
- // FIXME: This is only used to quickly check whether a given goal
- // is in the cache. We should experiment with using something like
- // `SsoHashSet` here because in most cases there are only a few entries.
- lookup_table: FxHashMap<CanonicalGoal<'tcx>, EntryIndex>,
-}
-
-impl<'tcx> ProvisionalCache<'tcx> {
- pub(super) fn empty() -> ProvisionalCache<'tcx> {
- ProvisionalCache {
- stack: Default::default(),
- entries: Default::default(),
- lookup_table: Default::default(),
- }
- }
-
- pub(super) fn current_depth(&self) -> usize {
- self.stack.len()
- }
-}
-
-impl<'tcx> EvalCtxt<'tcx> {
- /// Tries putting the new goal on the stack, returning an error if it is already cached.
- ///
- /// This correctly updates the provisional cache if there is a cycle.
- pub(super) fn try_push_stack(
- &mut self,
- goal: CanonicalGoal<'tcx>,
- ) -> Result<(), QueryResult<'tcx>> {
- // FIXME: start by checking the global cache
-
- // Look at the provisional cache to check for cycles.
- let cache = &mut self.provisional_cache;
- match cache.lookup_table.entry(goal) {
- // No entry, simply push this goal on the stack after dealing with overflow.
- Entry::Vacant(v) => {
- if self.overflow_data.has_overflow(cache.stack.len()) {
- return Err(self.deal_with_overflow(goal));
- }
-
- let depth = cache.stack.push(StackElem { goal, has_been_used: false });
- let response = response_no_constraints(self.tcx, goal, Certainty::Yes);
- let entry_index = cache.entries.push(ProvisionalEntry { response, depth, goal });
- v.insert(entry_index);
- Ok(())
- }
- // We have a nested goal which relies on a goal `root` deeper in the stack.
- //
- // We first store that we may have to rerun `evaluate_goal` for `root` in case the
- // provisional response is not equal to the final response. We also update the depth
- // of all goals which recursively depend on our current goal to depend on `root`
- // instead.
- //
- // Finally we can return either the provisional response for that goal if we have a
- // coinductive cycle or an ambiguous result if the cycle is inductive.
- Entry::Occupied(entry_index) => {
- let entry_index = *entry_index.get();
- // FIXME `ProvisionalEntry` should be `Copy`.
- let entry = cache.entries.get(entry_index).unwrap().clone();
- cache.stack[entry.depth].has_been_used = true;
- for provisional_entry in cache.entries.iter_mut().skip(entry_index.index()) {
- provisional_entry.depth = provisional_entry.depth.min(entry.depth);
- }
-
- // NOTE: The goals on the stack aren't the only goals involved in this cycle.
- // We can also depend on goals which aren't part of the stack but coinductively
- // depend on the stack themselves. We already checked whether all the goals
- // between these goals and their root on the stack. This means that as long as
- // each goal in a cycle is checked for coinductivity by itself, simply checking
- // the stack is enough.
- if cache.stack.raw[entry.depth.index()..]
- .iter()
- .all(|g| g.goal.value.predicate.is_coinductive(self.tcx))
- {
- Err(entry.response)
- } else {
- Err(response_no_constraints(
- self.tcx,
- goal,
- Certainty::Maybe(MaybeCause::Overflow),
- ))
- }
- }
- }
- }
-
- /// We cannot simply store the result of [EvalCtxt::compute_goal] as we have to deal with
- /// coinductive cycles.
- ///
- /// When we encounter a coinductive cycle, we have to prove the final result of that cycle
- /// while we are still computing that result. Because of this we continously recompute the
- /// cycle until the result of the previous iteration is equal to the final result, at which
- /// point we are done.
- ///
- /// This function returns `true` if we were able to finalize the goal and `false` if it has
- /// updated the provisional cache and we have to recompute the current goal.
- ///
- /// FIXME: Refer to the rustc-dev-guide entry once it exists.
- pub(super) fn try_finalize_goal(
- &mut self,
- actual_goal: CanonicalGoal<'tcx>,
- response: QueryResult<'tcx>,
- ) -> bool {
- let cache = &mut self.provisional_cache;
- let StackElem { goal, has_been_used } = cache.stack.pop().unwrap();
- assert_eq!(goal, actual_goal);
-
- let provisional_entry_index = *cache.lookup_table.get(&goal).unwrap();
- let provisional_entry = &mut cache.entries[provisional_entry_index];
- // Was the current goal the root of a cycle and was the provisional response
- // different from the final one.
- if has_been_used && provisional_entry.response != response {
- // If so, update the provisional reponse for this goal...
- provisional_entry.response = response;
- // ...remove all entries whose result depends on this goal
- // from the provisional cache...
- //
- // That's not completely correct, as a nested goal can also
- // depend on a goal which is lower in the stack so it doesn't
- // actually depend on the current goal. This should be fairly
- // rare and is hopefully not relevant for performance.
- #[allow(rustc::potential_query_instability)]
- cache.lookup_table.retain(|_key, index| *index <= provisional_entry_index);
- cache.entries.truncate(provisional_entry_index.index() + 1);
-
- // ...and finally push our goal back on the stack and reevaluate it.
- cache.stack.push(StackElem { goal, has_been_used: false });
- false
- } else {
- // If not, we're done with this goal.
- //
- // Check whether that this goal doesn't depend on a goal deeper on the stack
- // and if so, move it and all nested goals to the global cache.
- //
- // Note that if any nested goal were to depend on something deeper on the stack,
- // this would have also updated the depth of this goal.
- if provisional_entry.depth == cache.stack.next_index() {
- for (i, entry) in cache.entries.drain_enumerated(provisional_entry_index.index()..)
- {
- let actual_index = cache.lookup_table.remove(&entry.goal);
- debug_assert_eq!(Some(i), actual_index);
- Self::try_move_finished_goal_to_global_cache(
- self.tcx,
- &mut self.overflow_data,
- &cache.stack,
- entry.goal,
- entry.response,
- );
- }
- }
- true
- }
- }
-
- fn try_move_finished_goal_to_global_cache(
- tcx: TyCtxt<'tcx>,
- overflow_data: &mut OverflowData,
- stack: &IndexVec<StackDepth, StackElem<'tcx>>,
- goal: CanonicalGoal<'tcx>,
- response: QueryResult<'tcx>,
- ) {
- // We move goals to the global cache if we either did not hit an overflow or if it's
- // the root goal as that will now always hit the same overflow limit.
- //
- // NOTE: We cannot move any non-root goals to the global cache even if their final result
- // isn't impacted by the overflow as that goal still has unstable query dependencies
- // because it didn't go its full depth.
- //
- // FIXME(@lcnr): We could still cache subtrees which are not impacted by overflow though.
- // Tracking that info correctly isn't trivial, so I haven't implemented it for now.
- let should_cache_globally = !overflow_data.did_overflow() || stack.is_empty();
- if should_cache_globally {
- // FIXME: move the provisional entry to the global cache.
- let _ = (tcx, goal, response);
- }
- }
-}
-
-pub(super) fn response_no_constraints<'tcx>(
- tcx: TyCtxt<'tcx>,
- goal: Canonical<'tcx, impl Sized>,
- certainty: Certainty,
-) -> QueryResult<'tcx> {
- let var_values = goal
- .variables
- .iter()
- .enumerate()
- .map(|(i, info)| match info.kind {
- CanonicalVarKind::Ty(_) | CanonicalVarKind::PlaceholderTy(_) => {
- tcx.mk_ty(ty::Bound(ty::INNERMOST, ty::BoundVar::from_usize(i).into())).into()
- }
- CanonicalVarKind::Region(_) | CanonicalVarKind::PlaceholderRegion(_) => {
- let br = ty::BoundRegion {
- var: ty::BoundVar::from_usize(i),
- kind: ty::BrAnon(i as u32, None),
- };
- tcx.mk_region(ty::ReLateBound(ty::INNERMOST, br)).into()
- }
- CanonicalVarKind::Const(_, ty) | CanonicalVarKind::PlaceholderConst(_, ty) => tcx
- .mk_const(ty::ConstKind::Bound(ty::INNERMOST, ty::BoundVar::from_usize(i)), ty)
- .into(),
- })
- .collect();
-
- Ok(Canonical {
- max_universe: goal.max_universe,
- variables: goal.variables,
- value: Response {
- var_values: CanonicalVarValues { var_values },
- external_constraints: Default::default(),
- certainty,
- },
- })
-}
use rustc_data_structures::fx::FxHashMap;
use rustc_infer::{
- infer::InferCtxt,
+ infer::{canonical::OriginalQueryValues, InferCtxt},
traits::{
query::NoSolution, FulfillmentError, FulfillmentErrorCode, PredicateObligation,
SelectionError, TraitEngine,
let mut has_changed = false;
for obligation in mem::take(&mut self.obligations) {
- let mut cx = EvalCtxt::new(infcx.tcx);
- let (changed, certainty) = match cx.evaluate_goal(infcx, obligation.clone().into())
- {
- Ok(result) => result,
+ let goal = obligation.clone().into();
+
+ // FIXME: Add a better API for that '^^
+ let mut orig_values = OriginalQueryValues::default();
+ let canonical_goal = infcx.canonicalize_query(goal, &mut orig_values);
+ let (changed, certainty) = match EvalCtxt::evaluate_canonical_goal(
+ infcx.tcx,
+ &mut super::search_graph::SearchGraph::new(infcx.tcx),
+ canonical_goal,
+ ) {
+ Ok(canonical_response) => {
+ (
+ true, // FIXME: check whether `var_values` are an identity substitution.
+ super::instantiate_canonical_query_response(
+ infcx,
+ &orig_values,
+ canonical_response,
+ ),
+ )
+ }
Err(NoSolution) => {
errors.push(FulfillmentError {
obligation: obligation.clone(),
-use rustc_infer::infer::canonical::CanonicalVarValues;
use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
use rustc_infer::infer::InferCtxt;
-use rustc_infer::traits::query::NoSolution;
use rustc_middle::ty::Ty;
use rustc_span::DUMMY_SP;
-use crate::solve::ExternalConstraints;
-
-use super::{Certainty, QueryResult, Response};
-
/// Methods used inside of the canonical queries of the solver.
pub(super) trait InferCtxtExt<'tcx> {
fn next_ty_infer(&self) -> Ty<'tcx>;
-
- fn make_canonical_response(
- &self,
- var_values: CanonicalVarValues<'tcx>,
- certainty: Certainty,
- ) -> QueryResult<'tcx>;
}
impl<'tcx> InferCtxtExt<'tcx> for InferCtxt<'tcx> {
span: DUMMY_SP,
})
}
-
- fn make_canonical_response(
- &self,
- var_values: CanonicalVarValues<'tcx>,
- certainty: Certainty,
- ) -> QueryResult<'tcx> {
- let external_constraints = take_external_constraints(self)?;
-
- Ok(self.canonicalize_response(Response { var_values, external_constraints, certainty }))
- }
-}
-
-#[instrument(level = "debug", skip(infcx), ret)]
-fn take_external_constraints<'tcx>(
- infcx: &InferCtxt<'tcx>,
-) -> Result<ExternalConstraints<'tcx>, NoSolution> {
- let region_obligations = infcx.take_registered_region_obligations();
- let opaque_types = infcx.take_opaque_types_for_query_response();
- Ok(ExternalConstraints {
- // FIXME: Now that's definitely wrong :)
- //
- // Should also do the leak check here I think
- regions: drop(region_obligations),
- opaque_types,
- })
}
use std::mem;
+use rustc_infer::infer::canonical::{Canonical, CanonicalVarKind, CanonicalVarValues};
use rustc_infer::infer::canonical::{OriginalQueryValues, QueryRegionConstraints, QueryResponse};
use rustc_infer::infer::{InferCtxt, InferOk, TyCtxtInferExt};
use rustc_infer::traits::query::NoSolution;
use rustc_infer::traits::Obligation;
use rustc_middle::infer::canonical::Certainty as OldCertainty;
-use rustc_middle::infer::canonical::{Canonical, CanonicalVarValues};
use rustc_middle::ty::{self, Ty, TyCtxt};
use rustc_middle::ty::{RegionOutlivesPredicate, ToPredicate, TypeOutlivesPredicate};
use rustc_span::DUMMY_SP;
use crate::traits::ObligationCause;
-use self::cache::response_no_constraints;
-use self::infcx_ext::InferCtxtExt;
-
mod assembly;
-mod cache;
mod fulfill;
mod infcx_ext;
-mod overflow;
mod project_goals;
+mod search_graph;
mod trait_goals;
pub use fulfill::FulfillmentCtxt;
impl<'tcx> TyCtxtExt<'tcx> for TyCtxt<'tcx> {
fn evaluate_goal(self, goal: CanonicalGoal<'tcx>) -> QueryResult<'tcx> {
- let mut cx = EvalCtxt::new(self);
- cx.evaluate_canonical_goal(goal)
+ let mut search_graph = search_graph::SearchGraph::new(self);
+ EvalCtxt::evaluate_canonical_goal(self, &mut search_graph, goal)
}
}
-struct EvalCtxt<'tcx> {
- tcx: TyCtxt<'tcx>,
+struct EvalCtxt<'a, 'tcx> {
+ infcx: &'a InferCtxt<'tcx>,
+ var_values: CanonicalVarValues<'tcx>,
- provisional_cache: cache::ProvisionalCache<'tcx>,
- overflow_data: overflow::OverflowData,
+ search_graph: &'a mut search_graph::SearchGraph<'tcx>,
}
-impl<'tcx> EvalCtxt<'tcx> {
- fn new(tcx: TyCtxt<'tcx>) -> EvalCtxt<'tcx> {
- EvalCtxt {
- tcx,
- provisional_cache: cache::ProvisionalCache::empty(),
- overflow_data: overflow::OverflowData::new(tcx),
- }
- }
-
- /// Recursively evaluates `goal`, returning whether any inference vars have
- /// been constrained and the certainty of the result.
- fn evaluate_goal(
- &mut self,
- infcx: &InferCtxt<'tcx>,
- goal: Goal<'tcx, ty::Predicate<'tcx>>,
- ) -> Result<(bool, Certainty), NoSolution> {
- let mut orig_values = OriginalQueryValues::default();
- let canonical_goal = infcx.canonicalize_query(goal, &mut orig_values);
- let canonical_response = self.evaluate_canonical_goal(canonical_goal)?;
- Ok((
- !canonical_response.value.var_values.is_identity(),
- instantiate_canonical_query_response(infcx, &orig_values, canonical_response),
- ))
- }
-
- fn evaluate_canonical_goal(&mut self, goal: CanonicalGoal<'tcx>) -> QueryResult<'tcx> {
- match self.try_push_stack(goal) {
+impl<'a, 'tcx> EvalCtxt<'a, 'tcx> {
+ fn evaluate_canonical_goal(
+ tcx: TyCtxt<'tcx>,
+ search_graph: &'a mut search_graph::SearchGraph<'tcx>,
+ canonical_goal: CanonicalGoal<'tcx>,
+ ) -> QueryResult<'tcx> {
+ match search_graph.try_push_stack(tcx, canonical_goal) {
Ok(()) => {}
// Our goal is already on the stack, eager return.
Err(response) => return response,
//
// FIXME: Similar to `evaluate_all`, this has to check for overflow.
loop {
- let result = self.compute_goal(goal);
+ let (ref infcx, goal, var_values) =
+ tcx.infer_ctxt().build_with_canonical(DUMMY_SP, &canonical_goal);
+ let mut ecx = EvalCtxt { infcx, var_values, search_graph };
+ let result = ecx.compute_goal(goal);
// FIXME: `Response` should be `Copy`
- if self.try_finalize_goal(goal, result.clone()) {
+ if search_graph.try_finalize_goal(tcx, canonical_goal, result.clone()) {
return result;
}
}
}
- fn compute_goal(&mut self, canonical_goal: CanonicalGoal<'tcx>) -> QueryResult<'tcx> {
- // WARNING: We're looking at a canonical value without instantiating it here.
- //
- // We have to be incredibly careful to not change the order of bound variables or
- // remove any. As we go from `Goal<'tcx, Predicate>` to `Goal` with the variants
- // of `PredicateKind` this is the case and it is and faster than instantiating and
- // recanonicalizing.
- let Goal { param_env, predicate } = canonical_goal.value;
+ fn tcx(&self) -> TyCtxt<'tcx> {
+ self.infcx.tcx
+ }
+
+ fn make_canonical_response(&self, certainty: Certainty) -> QueryResult<'tcx> {
+ let external_constraints = take_external_constraints(self.infcx)?;
+
+ Ok(self.infcx.canonicalize_response(Response {
+ var_values: self.var_values.clone(),
+ external_constraints,
+ certainty,
+ }))
+ }
+
+ /// Recursively evaluates `goal`, returning whether any inference vars have
+ /// been constrained and the certainty of the result.
+ fn evaluate_goal(
+ &mut self,
+ goal: Goal<'tcx, ty::Predicate<'tcx>>,
+ ) -> Result<(bool, Certainty), NoSolution> {
+ let mut orig_values = OriginalQueryValues::default();
+ let canonical_goal = self.infcx.canonicalize_query(goal, &mut orig_values);
+ let canonical_response =
+ EvalCtxt::evaluate_canonical_goal(self.tcx(), self.search_graph, canonical_goal)?;
+ Ok((
+ !canonical_response.value.var_values.is_identity(),
+ instantiate_canonical_query_response(self.infcx, &orig_values, canonical_response),
+ ))
+ }
- if let Some(kind) = predicate.kind().no_bound_vars_ignoring_escaping(self.tcx) {
+ fn compute_goal(&mut self, goal: Goal<'tcx, ty::Predicate<'tcx>>) -> QueryResult<'tcx> {
+ let Goal { param_env, predicate } = goal;
+ let kind = predicate.kind();
+ if let Some(kind) = kind.no_bound_vars() {
match kind {
- ty::PredicateKind::Clause(ty::Clause::Trait(predicate)) => self.compute_trait_goal(
- canonical_goal.unchecked_rebind(Goal { param_env, predicate }),
- ),
- ty::PredicateKind::Clause(ty::Clause::Projection(predicate)) => self
- .compute_projection_goal(
- canonical_goal.unchecked_rebind(Goal { param_env, predicate }),
- ),
- ty::PredicateKind::Clause(ty::Clause::TypeOutlives(predicate)) => self
- .compute_type_outlives_goal(
- canonical_goal.unchecked_rebind(Goal { param_env, predicate }),
- ),
- ty::PredicateKind::Clause(ty::Clause::RegionOutlives(predicate)) => self
- .compute_region_outlives_goal(
- canonical_goal.unchecked_rebind(Goal { param_env, predicate }),
- ),
+ ty::PredicateKind::Clause(ty::Clause::Trait(predicate)) => {
+ self.compute_trait_goal(Goal { param_env, predicate })
+ }
+ ty::PredicateKind::Clause(ty::Clause::Projection(predicate)) => {
+ self.compute_projection_goal(Goal { param_env, predicate })
+ }
+ ty::PredicateKind::Clause(ty::Clause::TypeOutlives(predicate)) => {
+ self.compute_type_outlives_goal(Goal { param_env, predicate })
+ }
+ ty::PredicateKind::Clause(ty::Clause::RegionOutlives(predicate)) => {
+ self.compute_region_outlives_goal(Goal { param_env, predicate })
+ }
// FIXME: implement these predicates :)
ty::PredicateKind::WellFormed(_)
| ty::PredicateKind::ObjectSafe(_)
| ty::PredicateKind::ConstEvaluatable(_)
| ty::PredicateKind::ConstEquate(_, _)
| ty::PredicateKind::TypeWellFormedFromEnv(_)
- | ty::PredicateKind::Ambiguous => {
- // FIXME
- response_no_constraints(self.tcx, canonical_goal, Certainty::Yes)
- }
+ | ty::PredicateKind::Ambiguous => self.make_canonical_response(Certainty::Yes),
}
} else {
- let (infcx, goal, var_values) =
- self.tcx.infer_ctxt().build_with_canonical(DUMMY_SP, &canonical_goal);
- let kind = infcx.replace_bound_vars_with_placeholders(goal.predicate.kind());
- let goal = goal.with(self.tcx, ty::Binder::dummy(kind));
- let (_, certainty) = self.evaluate_goal(&infcx, goal)?;
- infcx.make_canonical_response(var_values, certainty)
+ let kind = self.infcx.replace_bound_vars_with_placeholders(kind);
+ let goal = goal.with(self.tcx(), ty::Binder::dummy(kind));
+ let (_, certainty) = self.evaluate_goal(goal)?;
+ self.make_canonical_response(certainty)
}
}
fn compute_type_outlives_goal(
&mut self,
- goal: CanonicalGoal<'tcx, TypeOutlivesPredicate<'tcx>>,
+ _goal: Goal<'tcx, TypeOutlivesPredicate<'tcx>>,
) -> QueryResult<'tcx> {
- // FIXME
- response_no_constraints(self.tcx, goal, Certainty::Yes)
+ self.make_canonical_response(Certainty::Yes)
}
fn compute_region_outlives_goal(
&mut self,
- goal: CanonicalGoal<'tcx, RegionOutlivesPredicate<'tcx>>,
+ _goal: Goal<'tcx, RegionOutlivesPredicate<'tcx>>,
) -> QueryResult<'tcx> {
- // FIXME
- response_no_constraints(self.tcx, goal, Certainty::Yes)
+ self.make_canonical_response(Certainty::Yes)
}
}
-impl<'tcx> EvalCtxt<'tcx> {
+impl<'tcx> EvalCtxt<'_, 'tcx> {
fn evaluate_all(
&mut self,
- infcx: &InferCtxt<'tcx>,
mut goals: Vec<Goal<'tcx, ty::Predicate<'tcx>>>,
) -> Result<Certainty, NoSolution> {
let mut new_goals = Vec::new();
self.repeat_while_none(|this| {
let mut has_changed = Err(Certainty::Yes);
for goal in goals.drain(..) {
- let (changed, certainty) = match this.evaluate_goal(infcx, goal) {
+ let (changed, certainty) = match this.evaluate_goal(goal) {
Ok(result) => result,
Err(NoSolution) => return Some(Err(NoSolution)),
};
}
}
+#[instrument(level = "debug", skip(infcx), ret)]
+fn take_external_constraints<'tcx>(
+ infcx: &InferCtxt<'tcx>,
+) -> Result<ExternalConstraints<'tcx>, NoSolution> {
+ let region_obligations = infcx.take_registered_region_obligations();
+ let opaque_types = infcx.take_opaque_types_for_query_response();
+ Ok(ExternalConstraints {
+ // FIXME: Now that's definitely wrong :)
+ //
+ // Should also do the leak check here I think
+ regions: drop(region_obligations),
+ opaque_types,
+ })
+}
+
fn instantiate_canonical_query_response<'tcx>(
infcx: &InferCtxt<'tcx>,
original_values: &OriginalQueryValues<'tcx>,
assert!(obligations.is_empty());
value
}
+
+pub(super) fn response_no_constraints<'tcx>(
+ tcx: TyCtxt<'tcx>,
+ goal: Canonical<'tcx, impl Sized>,
+ certainty: Certainty,
+) -> QueryResult<'tcx> {
+ let var_values = goal
+ .variables
+ .iter()
+ .enumerate()
+ .map(|(i, info)| match info.kind {
+ CanonicalVarKind::Ty(_) | CanonicalVarKind::PlaceholderTy(_) => {
+ tcx.mk_ty(ty::Bound(ty::INNERMOST, ty::BoundVar::from_usize(i).into())).into()
+ }
+ CanonicalVarKind::Region(_) | CanonicalVarKind::PlaceholderRegion(_) => {
+ let br = ty::BoundRegion {
+ var: ty::BoundVar::from_usize(i),
+ kind: ty::BrAnon(i as u32, None),
+ };
+ tcx.mk_region(ty::ReLateBound(ty::INNERMOST, br)).into()
+ }
+ CanonicalVarKind::Const(_, ty) | CanonicalVarKind::PlaceholderConst(_, ty) => tcx
+ .mk_const(ty::ConstKind::Bound(ty::INNERMOST, ty::BoundVar::from_usize(i)), ty)
+ .into(),
+ })
+ .collect();
+
+ Ok(Canonical {
+ max_universe: goal.max_universe,
+ variables: goal.variables,
+ value: Response {
+ var_values: CanonicalVarValues { var_values },
+ external_constraints: Default::default(),
+ certainty,
+ },
+ })
+}
+++ /dev/null
-use rustc_infer::infer::canonical::Canonical;
-use rustc_infer::traits::query::NoSolution;
-use rustc_middle::ty::TyCtxt;
-use rustc_session::Limit;
-
-use super::cache::response_no_constraints;
-use super::{Certainty, EvalCtxt, MaybeCause, QueryResult};
-
-/// When detecting a solver overflow, we return ambiguity. Overflow can be
-/// *hidden* by either a fatal error in an **AND** or a trivial success in an **OR**.
-///
-/// This is in issue in case of exponential blowup, e.g. if each goal on the stack
-/// has multiple nested (overflowing) candidates. To deal with this, we reduce the limit
-/// used by the solver when hitting the default limit for the first time.
-///
-/// FIXME: Get tests where always using the `default_limit` results in a hang and refer
-/// to them here. We can also improve the overflow strategy if necessary.
-pub(super) struct OverflowData {
- default_limit: Limit,
- current_limit: Limit,
- /// When proving an **AND** we have to repeatedly iterate over the yet unproven goals.
- ///
- /// Because of this each iteration also increases the depth in addition to the stack
- /// depth.
- additional_depth: usize,
-}
-
-impl OverflowData {
- pub(super) fn new(tcx: TyCtxt<'_>) -> OverflowData {
- let default_limit = tcx.recursion_limit();
- OverflowData { default_limit, current_limit: default_limit, additional_depth: 0 }
- }
-
- #[inline]
- pub(super) fn did_overflow(&self) -> bool {
- self.default_limit.0 != self.current_limit.0
- }
-
- #[inline]
- pub(super) fn has_overflow(&self, depth: usize) -> bool {
- !self.current_limit.value_within_limit(depth + self.additional_depth)
- }
-
- /// Updating the current limit when hitting overflow.
- fn deal_with_overflow(&mut self) {
- // When first hitting overflow we reduce the overflow limit
- // for all future goals to prevent hangs if there's an exponental
- // blowup.
- self.current_limit.0 = self.default_limit.0 / 8;
- }
-}
-
-impl<'tcx> EvalCtxt<'tcx> {
- pub(super) fn deal_with_overflow(
- &mut self,
- goal: Canonical<'tcx, impl Sized>,
- ) -> QueryResult<'tcx> {
- self.overflow_data.deal_with_overflow();
- response_no_constraints(self.tcx, goal, Certainty::Maybe(MaybeCause::Overflow))
- }
-
- /// A `while`-loop which tracks overflow.
- pub(super) fn repeat_while_none(
- &mut self,
- mut loop_body: impl FnMut(&mut Self) -> Option<Result<Certainty, NoSolution>>,
- ) -> Result<Certainty, NoSolution> {
- let start_depth = self.overflow_data.additional_depth;
- let depth = self.provisional_cache.current_depth();
- while !self.overflow_data.has_overflow(depth) {
- if let Some(result) = loop_body(self) {
- self.overflow_data.additional_depth = start_depth;
- return result;
- }
-
- self.overflow_data.additional_depth += 1;
- }
- self.overflow_data.additional_depth = start_depth;
- self.overflow_data.deal_with_overflow();
- Ok(Certainty::Maybe(MaybeCause::Overflow))
- }
-}
use crate::traits::{specialization_graph, translate_substs};
use super::assembly::{self, AssemblyCtxt};
-use super::{CanonicalGoal, EvalCtxt, Goal, QueryResult};
+use super::{EvalCtxt, Goal, QueryResult};
use rustc_errors::ErrorGuaranteed;
use rustc_hir::def::DefKind;
use rustc_hir::def_id::DefId;
type Candidate<'tcx> = assembly::Candidate<'tcx, ProjectionPredicate<'tcx>>;
-impl<'tcx> EvalCtxt<'tcx> {
+impl<'tcx> EvalCtxt<'_, 'tcx> {
pub(super) fn compute_projection_goal(
&mut self,
- goal: CanonicalGoal<'tcx, ProjectionPredicate<'tcx>>,
+ goal: Goal<'tcx, ProjectionPredicate<'tcx>>,
) -> QueryResult<'tcx> {
let candidates = AssemblyCtxt::assemble_and_evaluate_candidates(self, goal);
self.merge_project_candidates(candidates)
}
fn consider_impl_candidate(
- acx: &mut AssemblyCtxt<'_, 'tcx, ProjectionPredicate<'tcx>>,
+ acx: &mut AssemblyCtxt<'_, '_, 'tcx, ProjectionPredicate<'tcx>>,
goal: Goal<'tcx, ProjectionPredicate<'tcx>>,
impl_def_id: DefId,
) {
- let tcx = acx.cx.tcx;
+ let tcx = acx.cx.tcx();
+ let infcx = acx.cx.infcx;
+
let goal_trait_ref = goal.predicate.projection_ty.trait_ref(tcx);
let impl_trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap();
let drcx = DeepRejectCtxt { treat_obligation_params: TreatParams::AsPlaceholder };
return;
}
- acx.infcx.probe(|_| {
- let impl_substs = acx.infcx.fresh_substs_for_item(DUMMY_SP, impl_def_id);
+ infcx.probe(|_| {
+ let impl_substs = infcx.fresh_substs_for_item(DUMMY_SP, impl_def_id);
let impl_trait_ref = impl_trait_ref.subst(tcx, impl_substs);
- let Ok(InferOk { obligations, .. }) = acx
- .infcx
+ let Ok(InferOk { obligations, .. }) = infcx
.at(&ObligationCause::dummy(), goal.param_env)
.define_opaque_types(false)
.eq(goal_trait_ref, impl_trait_ref)
.into_iter()
.map(|pred| goal.with(tcx, pred));
- let nested_goals = obligations.into_iter().map(|o| o.into()).chain(where_clause_bounds).collect();
- let Ok(trait_ref_certainty) = acx.cx.evaluate_all(acx.infcx, nested_goals) else { return };
+ let nested_goals =
+ obligations.into_iter().map(|o| o.into()).chain(where_clause_bounds).collect();
+ let Ok(trait_ref_certainty) = acx.cx.evaluate_all(nested_goals) else { return };
let Some(assoc_def) = fetch_eligible_assoc_item_def(
- acx.infcx,
+ infcx,
goal.param_env,
goal_trait_ref,
goal.predicate.def_id(),
impl_substs,
);
let substs = translate_substs(
- acx.infcx,
+ infcx,
goal.param_env,
impl_def_id,
impl_substs_with_gat,
let is_const = matches!(tcx.def_kind(assoc_def.item.def_id), DefKind::AssocConst);
let ty = tcx.bound_type_of(assoc_def.item.def_id);
let term: ty::EarlyBinder<ty::Term<'tcx>> = if is_const {
- let identity_substs = ty::InternalSubsts::identity_for_item(tcx, assoc_def.item.def_id);
+ let identity_substs =
+ ty::InternalSubsts::identity_for_item(tcx, assoc_def.item.def_id);
let did = ty::WithOptConstParam::unknown(assoc_def.item.def_id);
let kind =
ty::ConstKind::Unevaluated(ty::UnevaluatedConst::new(did, identity_substs));
ty.map_bound(|ty| ty.into())
};
- let Ok(InferOk { obligations, .. }) = acx
- .infcx
+ let Ok(InferOk { obligations, .. }) = infcx
.at(&ObligationCause::dummy(), goal.param_env)
.define_opaque_types(false)
.eq(goal.predicate.term, term.subst(tcx, substs))
};
let nested_goals = obligations.into_iter().map(|o| o.into()).collect();
- let Ok(rhs_certainty) = acx.cx.evaluate_all(acx.infcx, nested_goals) else { return };
+ let Ok(rhs_certainty) = acx.cx.evaluate_all(nested_goals) else { return };
let certainty = trait_ref_certainty.unify_and(rhs_certainty);
acx.try_insert_candidate(CandidateSource::Impl(impl_def_id), certainty);
--- /dev/null
+//! This module both handles the global cache which stores "finished" goals,
+//! and the provisional cache which contains partially computed goals.
+//!
+//! The provisional cache is necessary when dealing with coinductive cycles.
+//!
+//! For more information about the provisional cache and coinduction in general,
+//! check out the relevant section of the rustc-dev-guide.
+//!
+//! FIXME(@lcnr): Write that section, feel free to ping me if you need help here
+//! before then or if I still haven't done that before January 2023.
+use super::overflow::OverflowData;
+use super::StackDepth;
+use crate::solve::{CanonicalGoal, QueryResult};
+use rustc_data_structures::fx::FxHashMap;
+use rustc_index::vec::IndexVec;
+use rustc_middle::ty::TyCtxt;
+
+rustc_index::newtype_index! {
+ pub struct EntryIndex {}
+}
+
+#[derive(Debug, Clone)]
+pub(super) struct ProvisionalEntry<'tcx> {
+ // In case we have a coinductive cycle, this is the
+ // the currently least restrictive result of this goal.
+ pub(super) response: QueryResult<'tcx>,
+ // In case of a cycle, the position of deepest stack entry involved
+ // in that cycle. This is monotonically decreasing in the stack as all
+ // elements between the current stack element in the deepest stack entry
+ // involved have to also be involved in that cycle.
+ //
+ // We can only move entries to the global cache once we're complete done
+ // with the cycle. If this entry has not been involved in a cycle,
+ // this is just its own depth.
+ pub(super) depth: StackDepth,
+
+ // The goal for this entry. Should always be equal to the corresponding goal
+ // in the lookup table.
+ pub(super) goal: CanonicalGoal<'tcx>,
+}
+
+pub(super) struct ProvisionalCache<'tcx> {
+ pub(super) entries: IndexVec<EntryIndex, ProvisionalEntry<'tcx>>,
+ // FIXME: This is only used to quickly check whether a given goal
+ // is in the cache. We should experiment with using something like
+ // `SsoHashSet` here because in most cases there are only a few entries.
+ pub(super) lookup_table: FxHashMap<CanonicalGoal<'tcx>, EntryIndex>,
+}
+
+impl<'tcx> ProvisionalCache<'tcx> {
+ pub(super) fn empty() -> ProvisionalCache<'tcx> {
+ ProvisionalCache { entries: Default::default(), lookup_table: Default::default() }
+ }
+
+ /// Adds a dependency from the current leaf to `target` in the cache
+ /// to prevent us from moving any goals which depend on the current leaf
+ /// to the global cache while we're still computing `target`.
+ pub(super) fn add_dependency_of_leaf_on(&mut self, target: EntryIndex) {
+ let depth = self.entries[target].depth;
+ for provisional_entry in &mut self.entries.raw[target.index()..] {
+ // The depth of `target` is the position of the deepest goal in the stack
+ // on which `target` depends. That goal is the `root` of this cycle.
+ //
+ // Any entry which was added after `target` is either on the stack itself
+ // at which point its depth is definitely at least as high as the depth of
+ // `root`. If it's not on the stack itself it has to depend on a goal
+ // between `root` and `leaf`. If it were to depend on a goal deeper in the
+ // stack than `root`, then `root` would also depend on that goal, at which
+ // point `root` wouldn't be the root anymore.
+ debug_assert!(provisional_entry.depth >= depth);
+ provisional_entry.depth = depth;
+ }
+
+ // We only update entries which were added after `target` as no other
+ // entry should have a higher depth.
+ //
+ // Any entry which previously had a higher depth than target has to
+ // be between `target` and `root`. Because of this we would have updated
+ // its depth when calling `add_dependency_of_leaf_on(root)` for `target`.
+ if cfg!(debug_assertions) {
+ self.entries.iter().all(|e| e.depth <= depth);
+ }
+ }
+
+ pub(super) fn depth(&self, entry_index: EntryIndex) -> StackDepth {
+ self.entries[entry_index].depth
+ }
+
+ pub(super) fn provisional_result(&self, entry_index: EntryIndex) -> QueryResult<'tcx> {
+ self.entries[entry_index].response.clone()
+ }
+}
+
+pub(super) fn try_move_finished_goal_to_global_cache<'tcx>(
+ tcx: TyCtxt<'tcx>,
+ overflow_data: &mut OverflowData,
+ stack: &IndexVec<super::StackDepth, super::StackElem<'tcx>>,
+ goal: CanonicalGoal<'tcx>,
+ response: QueryResult<'tcx>,
+) {
+ // We move goals to the global cache if we either did not hit an overflow or if it's
+ // the root goal as that will now always hit the same overflow limit.
+ //
+ // NOTE: We cannot move any non-root goals to the global cache even if their final result
+ // isn't impacted by the overflow as that goal still has unstable query dependencies
+ // because it didn't go its full depth.
+ //
+ // FIXME(@lcnr): We could still cache subtrees which are not impacted by overflow though.
+ // Tracking that info correctly isn't trivial, so I haven't implemented it for now.
+ let should_cache_globally = !overflow_data.did_overflow() || stack.is_empty();
+ if should_cache_globally {
+ // FIXME: move the provisional entry to the global cache.
+ let _ = (tcx, goal, response);
+ }
+}
--- /dev/null
+mod cache;
+mod overflow;
+
+use self::cache::ProvisionalEntry;
+use super::{CanonicalGoal, Certainty, MaybeCause, QueryResult};
+use cache::ProvisionalCache;
+use overflow::OverflowData;
+use rustc_index::vec::IndexVec;
+use rustc_middle::ty::TyCtxt;
+use std::collections::hash_map::Entry;
+
+rustc_index::newtype_index! {
+ pub struct StackDepth {}
+}
+
+struct StackElem<'tcx> {
+ goal: CanonicalGoal<'tcx>,
+ has_been_used: bool,
+}
+
+pub(super) struct SearchGraph<'tcx> {
+ /// The stack of goals currently being computed.
+ ///
+ /// An element is *deeper* in the stack if its index is *lower*.
+ stack: IndexVec<StackDepth, StackElem<'tcx>>,
+ overflow_data: OverflowData,
+ provisional_cache: ProvisionalCache<'tcx>,
+}
+
+impl<'tcx> SearchGraph<'tcx> {
+ pub(super) fn new(tcx: TyCtxt<'tcx>) -> SearchGraph<'tcx> {
+ Self {
+ stack: Default::default(),
+ overflow_data: OverflowData::new(tcx),
+ provisional_cache: ProvisionalCache::empty(),
+ }
+ }
+
+ /// Tries putting the new goal on the stack, returning an error if it is already cached.
+ ///
+ /// This correctly updates the provisional cache if there is a cycle.
+ pub(super) fn try_push_stack(
+ &mut self,
+ tcx: TyCtxt<'tcx>,
+ goal: CanonicalGoal<'tcx>,
+ ) -> Result<(), QueryResult<'tcx>> {
+ // FIXME: start by checking the global cache
+
+ // Look at the provisional cache to check for cycles.
+ let cache = &mut self.provisional_cache;
+ match cache.lookup_table.entry(goal) {
+ // No entry, simply push this goal on the stack after dealing with overflow.
+ Entry::Vacant(v) => {
+ if self.overflow_data.has_overflow(self.stack.len()) {
+ return Err(self.deal_with_overflow(tcx, goal));
+ }
+
+ let depth = self.stack.push(StackElem { goal, has_been_used: false });
+ let response = super::response_no_constraints(tcx, goal, Certainty::Yes);
+ let entry_index = cache.entries.push(ProvisionalEntry { response, depth, goal });
+ v.insert(entry_index);
+ Ok(())
+ }
+ // We have a nested goal which relies on a goal `root` deeper in the stack.
+ //
+ // We first store that we may have to rerun `evaluate_goal` for `root` in case the
+ // provisional response is not equal to the final response. We also update the depth
+ // of all goals which recursively depend on our current goal to depend on `root`
+ // instead.
+ //
+ // Finally we can return either the provisional response for that goal if we have a
+ // coinductive cycle or an ambiguous result if the cycle is inductive.
+ Entry::Occupied(entry_index) => {
+ let entry_index = *entry_index.get();
+
+ cache.add_dependency_of_leaf_on(entry_index);
+ let stack_depth = cache.depth(entry_index);
+
+ self.stack[stack_depth].has_been_used = true;
+ // NOTE: The goals on the stack aren't the only goals involved in this cycle.
+ // We can also depend on goals which aren't part of the stack but coinductively
+ // depend on the stack themselves. We already checked whether all the goals
+ // between these goals and their root on the stack. This means that as long as
+ // each goal in a cycle is checked for coinductivity by itself, simply checking
+ // the stack is enough.
+ if self.stack.raw[stack_depth.index()..]
+ .iter()
+ .all(|g| g.goal.value.predicate.is_coinductive(tcx))
+ {
+ Err(cache.provisional_result(entry_index))
+ } else {
+ Err(super::response_no_constraints(
+ tcx,
+ goal,
+ Certainty::Maybe(MaybeCause::Overflow),
+ ))
+ }
+ }
+ }
+ }
+
+ /// We cannot simply store the result of [EvalCtxt::compute_goal] as we have to deal with
+ /// coinductive cycles.
+ ///
+ /// When we encounter a coinductive cycle, we have to prove the final result of that cycle
+ /// while we are still computing that result. Because of this we continously recompute the
+ /// cycle until the result of the previous iteration is equal to the final result, at which
+ /// point we are done.
+ ///
+ /// This function returns `true` if we were able to finalize the goal and `false` if it has
+ /// updated the provisional cache and we have to recompute the current goal.
+ ///
+ /// FIXME: Refer to the rustc-dev-guide entry once it exists.
+ pub(super) fn try_finalize_goal(
+ &mut self,
+ tcx: TyCtxt<'tcx>,
+ actual_goal: CanonicalGoal<'tcx>,
+ response: QueryResult<'tcx>,
+ ) -> bool {
+ let StackElem { goal, has_been_used } = self.stack.pop().unwrap();
+ assert_eq!(goal, actual_goal);
+
+ let cache = &mut self.provisional_cache;
+ let provisional_entry_index = *cache.lookup_table.get(&goal).unwrap();
+ let provisional_entry = &mut cache.entries[provisional_entry_index];
+ let depth = provisional_entry.depth;
+ // Was the current goal the root of a cycle and was the provisional response
+ // different from the final one.
+ if has_been_used && provisional_entry.response != response {
+ // If so, update the provisional reponse for this goal...
+ provisional_entry.response = response;
+ // ...remove all entries whose result depends on this goal
+ // from the provisional cache...
+ //
+ // That's not completely correct, as a nested goal can also
+ // depend on a goal which is lower in the stack so it doesn't
+ // actually depend on the current goal. This should be fairly
+ // rare and is hopefully not relevant for performance.
+ #[allow(rustc::potential_query_instability)]
+ cache.lookup_table.retain(|_key, index| *index <= provisional_entry_index);
+ cache.entries.truncate(provisional_entry_index.index() + 1);
+
+ // ...and finally push our goal back on the stack and reevaluate it.
+ self.stack.push(StackElem { goal, has_been_used: false });
+ false
+ } else {
+ // If not, we're done with this goal.
+ //
+ // Check whether that this goal doesn't depend on a goal deeper on the stack
+ // and if so, move it and all nested goals to the global cache.
+ //
+ // Note that if any nested goal were to depend on something deeper on the stack,
+ // this would have also updated the depth of the current goal.
+ if depth == self.stack.next_index() {
+ for (i, entry) in cache.entries.drain_enumerated(provisional_entry_index.index()..)
+ {
+ let actual_index = cache.lookup_table.remove(&entry.goal);
+ debug_assert_eq!(Some(i), actual_index);
+ debug_assert!(entry.depth == depth);
+ cache::try_move_finished_goal_to_global_cache(
+ tcx,
+ &mut self.overflow_data,
+ &self.stack,
+ entry.goal,
+ entry.response,
+ );
+ }
+ }
+ true
+ }
+ }
+}
--- /dev/null
+use rustc_infer::infer::canonical::Canonical;
+use rustc_infer::traits::query::NoSolution;
+use rustc_middle::ty::TyCtxt;
+use rustc_session::Limit;
+
+use super::SearchGraph;
+use crate::solve::{response_no_constraints, Certainty, EvalCtxt, MaybeCause, QueryResult};
+
+/// When detecting a solver overflow, we return ambiguity. Overflow can be
+/// *hidden* by either a fatal error in an **AND** or a trivial success in an **OR**.
+///
+/// This is in issue in case of exponential blowup, e.g. if each goal on the stack
+/// has multiple nested (overflowing) candidates. To deal with this, we reduce the limit
+/// used by the solver when hitting the default limit for the first time.
+///
+/// FIXME: Get tests where always using the `default_limit` results in a hang and refer
+/// to them here. We can also improve the overflow strategy if necessary.
+pub(super) struct OverflowData {
+ default_limit: Limit,
+ current_limit: Limit,
+ /// When proving an **AND** we have to repeatedly iterate over the yet unproven goals.
+ ///
+ /// Because of this each iteration also increases the depth in addition to the stack
+ /// depth.
+ additional_depth: usize,
+}
+
+impl OverflowData {
+ pub(super) fn new(tcx: TyCtxt<'_>) -> OverflowData {
+ let default_limit = tcx.recursion_limit();
+ OverflowData { default_limit, current_limit: default_limit, additional_depth: 0 }
+ }
+
+ #[inline]
+ pub(super) fn did_overflow(&self) -> bool {
+ self.default_limit.0 != self.current_limit.0
+ }
+
+ #[inline]
+ pub(super) fn has_overflow(&self, depth: usize) -> bool {
+ !self.current_limit.value_within_limit(depth + self.additional_depth)
+ }
+
+ /// Updating the current limit when hitting overflow.
+ fn deal_with_overflow(&mut self) {
+ // When first hitting overflow we reduce the overflow limit
+ // for all future goals to prevent hangs if there's an exponental
+ // blowup.
+ self.current_limit.0 = self.default_limit.0 / 8;
+ }
+}
+
+impl<'tcx> SearchGraph<'tcx> {
+ pub fn deal_with_overflow(
+ &mut self,
+ tcx: TyCtxt<'tcx>,
+ goal: Canonical<'tcx, impl Sized>,
+ ) -> QueryResult<'tcx> {
+ self.overflow_data.deal_with_overflow();
+ response_no_constraints(tcx, goal, Certainty::Maybe(MaybeCause::Overflow))
+ }
+}
+
+impl<'tcx> EvalCtxt<'_, 'tcx> {
+ /// A `while`-loop which tracks overflow.
+ pub fn repeat_while_none(
+ &mut self,
+ mut loop_body: impl FnMut(&mut Self) -> Option<Result<Certainty, NoSolution>>,
+ ) -> Result<Certainty, NoSolution> {
+ let start_depth = self.search_graph.overflow_data.additional_depth;
+ let depth = self.search_graph.stack.len();
+ while !self.search_graph.overflow_data.has_overflow(depth) {
+ if let Some(result) = loop_body(self) {
+ self.search_graph.overflow_data.additional_depth = start_depth;
+ return result;
+ }
+
+ self.search_graph.overflow_data.additional_depth += 1;
+ }
+ self.search_graph.overflow_data.additional_depth = start_depth;
+ self.search_graph.overflow_data.deal_with_overflow();
+ Ok(Certainty::Maybe(MaybeCause::Overflow))
+ }
+}
use std::iter;
use super::assembly::{self, AssemblyCtxt};
-use super::{CanonicalGoal, EvalCtxt, Goal, QueryResult};
+use super::{EvalCtxt, Goal, QueryResult};
use rustc_hir::def_id::DefId;
use rustc_infer::infer::InferOk;
use rustc_infer::traits::query::NoSolution;
}
fn consider_impl_candidate(
- acx: &mut AssemblyCtxt<'_, 'tcx, Self>,
+ acx: &mut AssemblyCtxt<'_, '_, 'tcx, Self>,
goal: Goal<'tcx, TraitPredicate<'tcx>>,
impl_def_id: DefId,
) {
- let tcx = acx.cx.tcx;
+ let tcx = acx.cx.tcx();
+ let infcx = acx.cx.infcx;
let impl_trait_ref = tcx.impl_trait_ref(impl_def_id).unwrap();
let drcx = DeepRejectCtxt { treat_obligation_params: TreatParams::AsPlaceholder };
return;
}
- acx.infcx.probe(|_| {
- let impl_substs = acx.infcx.fresh_substs_for_item(DUMMY_SP, impl_def_id);
+ infcx.probe(|_| {
+ let impl_substs = infcx.fresh_substs_for_item(DUMMY_SP, impl_def_id);
let impl_trait_ref = impl_trait_ref.subst(tcx, impl_substs);
- let Ok(InferOk { obligations, .. }) = acx
- .infcx
+ let Ok(InferOk { obligations, .. }) = infcx
.at(&ObligationCause::dummy(), goal.param_env)
.define_opaque_types(false)
.eq(goal.predicate.trait_ref, impl_trait_ref)
let nested_goals =
obligations.into_iter().map(|o| o.into()).chain(where_clause_bounds).collect();
- let Ok(certainty) = acx.cx.evaluate_all(acx.infcx, nested_goals) else { return };
+ let Ok(certainty) = acx.cx.evaluate_all(nested_goals) else { return };
acx.try_insert_candidate(CandidateSource::Impl(impl_def_id), certainty);
})
}
}
-impl<'tcx> EvalCtxt<'tcx> {
+impl<'tcx> EvalCtxt<'_, 'tcx> {
pub(super) fn compute_trait_goal(
&mut self,
- goal: CanonicalGoal<'tcx, TraitPredicate<'tcx>>,
+ goal: Goal<'tcx, TraitPredicate<'tcx>>,
) -> QueryResult<'tcx> {
let candidates = AssemblyCtxt::assemble_and_evaluate_candidates(self, goal);
self.merge_trait_candidates_discard_reservation_impls(candidates)
fn discard_reservation_impl(&self, candidate: Candidate<'tcx>) -> Candidate<'tcx> {
if let CandidateSource::Impl(def_id) = candidate.source {
- if let ty::ImplPolarity::Reservation = self.tcx.impl_polarity(def_id) {
+ if let ty::ImplPolarity::Reservation = self.tcx().impl_polarity(def_id) {
debug!("Selected reservation impl");
// FIXME: reduce candidate to ambiguous
// FIXME: replace `var_values` with identity, yeet external constraints.
projects / rust.git / commitdiff