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enable fuzzing of SearchGraph

Browse Source 
fully move it into `rustc_type_ir` and make it
independent of `Interner`.
This commit is contained in:
lcnr 2024-07-11 23:13:12 +02:00 committed by Michael Goulet
parent f56b2074c6
commit 15f770b143
13 changed files with 986 additions and 761 deletions
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4
compiler/rustc_middle/src/traits/solve.rs
View File

@ -8,10 +8,6 @@ use crate::ty::{
self, FallibleTypeFolder, TyCtxt, TypeFoldable, TypeFolder, TypeVisitable, TypeVisitor,
};
mod cache;
pub use cache::EvaluationCache;
pub type Goal<'tcx, P> = ir::solve::Goal<TyCtxt<'tcx>, P>;
pub type QueryInput<'tcx, P> = ir::solve::QueryInput<TyCtxt<'tcx>, P>;
pub type QueryResult<'tcx> = ir::solve::QueryResult<TyCtxt<'tcx>>;

121
compiler/rustc_middle/src/traits/solve/cache.rs
View File

@ -1,121 +0,0 @@
use super::{inspect, CanonicalInput, QueryResult};
use crate::ty::TyCtxt;
use rustc_data_structures::fx::{FxHashMap, FxHashSet};
use rustc_data_structures::sync::Lock;
use rustc_query_system::cache::WithDepNode;
use rustc_query_system::dep_graph::DepNodeIndex;
use rustc_session::Limit;
use rustc_type_ir::solve::CacheData;
/// The trait solver cache used by `-Znext-solver`.
///
/// FIXME(@lcnr): link to some official documentation of how
/// this works.
#[derive(Default)]
pub struct EvaluationCache<'tcx> {
map: Lock<FxHashMap<CanonicalInput<'tcx>, CacheEntry<'tcx>>>,
}
impl<'tcx> rustc_type_ir::inherent::EvaluationCache<TyCtxt<'tcx>> for &'tcx EvaluationCache<'tcx> {
/// Insert a final result into the global cache.
fn insert(
&self,
tcx: TyCtxt<'tcx>,
key: CanonicalInput<'tcx>,
proof_tree: Option<&'tcx inspect::CanonicalGoalEvaluationStep<TyCtxt<'tcx>>>,
additional_depth: usize,
encountered_overflow: bool,
cycle_participants: FxHashSet<CanonicalInput<'tcx>>,
dep_node: DepNodeIndex,
result: QueryResult<'tcx>,
) {
let mut map = self.map.borrow_mut();
let entry = map.entry(key).or_default();
let data = WithDepNode::new(dep_node, QueryData { result, proof_tree });
entry.cycle_participants.extend(cycle_participants);
if encountered_overflow {
entry.with_overflow.insert(additional_depth, data);
} else {
entry.success = Some(Success { data, additional_depth });
}
if cfg!(debug_assertions) {
drop(map);
let expected = CacheData { result, proof_tree, additional_depth, encountered_overflow };
let actual = self.get(tcx, key, [], additional_depth);
if !actual.as_ref().is_some_and(|actual| expected == *actual) {
bug!("failed to lookup inserted element for {key:?}: {expected:?} != {actual:?}");
}
}
}
/// Try to fetch a cached result, checking the recursion limit
/// and handling root goals of coinductive cycles.
///
/// If this returns `Some` the cache result can be used.
fn get(
&self,
tcx: TyCtxt<'tcx>,
key: CanonicalInput<'tcx>,
stack_entries: impl IntoIterator<Item = CanonicalInput<'tcx>>,
available_depth: usize,
) -> Option<CacheData<TyCtxt<'tcx>>> {
let map = self.map.borrow();
let entry = map.get(&key)?;
for stack_entry in stack_entries {
if entry.cycle_participants.contains(&stack_entry) {
return None;
}
}
if let Some(ref success) = entry.success {
if Limit(available_depth).value_within_limit(success.additional_depth) {
let QueryData { result, proof_tree } = success.data.get(tcx);
return Some(CacheData {
result,
proof_tree,
additional_depth: success.additional_depth,
encountered_overflow: false,
});
}
}
entry.with_overflow.get(&available_depth).map(|e| {
let QueryData { result, proof_tree } = e.get(tcx);
CacheData {
result,
proof_tree,
additional_depth: available_depth,
encountered_overflow: true,
}
})
}
}
struct Success<'tcx> {
data: WithDepNode<QueryData<'tcx>>,
additional_depth: usize,
}
#[derive(Clone, Copy)]
pub struct QueryData<'tcx> {
pub result: QueryResult<'tcx>,
pub proof_tree: Option<&'tcx inspect::CanonicalGoalEvaluationStep<TyCtxt<'tcx>>>,
}
/// The cache entry for a goal `CanonicalInput`.
///
/// This contains results whose computation never hit the
/// recursion limit in `success`, and all results which hit
/// the recursion limit in `with_overflow`.
#[derive(Default)]
struct CacheEntry<'tcx> {
success: Option<Success<'tcx>>,
/// We have to be careful when caching roots of cycles.
///
/// See the doc comment of `StackEntry::cycle_participants` for more
/// details.
cycle_participants: FxHashSet<CanonicalInput<'tcx>>,
with_overflow: FxHashMap<usize, WithDepNode<QueryData<'tcx>>>,
}

29
compiler/rustc_middle/src/ty/context.rs
View File

@ -59,6 +59,7 @@ use rustc_hir::lang_items::LangItem;
use rustc_hir::{HirId, Node, TraitCandidate};
use rustc_index::IndexVec;
use rustc_macros::{HashStable, TyDecodable, TyEncodable};
use rustc_query_system::cache::WithDepNode;
use rustc_query_system::dep_graph::DepNodeIndex;
use rustc_query_system::ich::StableHashingContext;
use rustc_serialize::opaque::{FileEncodeResult, FileEncoder};
@ -75,7 +76,7 @@ use rustc_type_ir::fold::TypeFoldable;
use rustc_type_ir::lang_items::TraitSolverLangItem;
use rustc_type_ir::solve::SolverMode;
use rustc_type_ir::TyKind::*;
use rustc_type_ir::{CollectAndApply, Interner, TypeFlags, WithCachedTypeInfo};
use rustc_type_ir::{search_graph, CollectAndApply, Interner, TypeFlags, WithCachedTypeInfo};
use tracing::{debug, instrument};
use std::assert_matches::assert_matches;
@ -164,12 +165,26 @@ impl<'tcx> Interner for TyCtxt<'tcx> {
type Clause = Clause<'tcx>;
type Clauses = ty::Clauses<'tcx>;
type EvaluationCache = &'tcx solve::EvaluationCache<'tcx>;
type Tracked<T: fmt::Debug + Clone> = WithDepNode<T>;
fn mk_tracked<T: fmt::Debug + Clone>(
self,
data: T,
dep_node: DepNodeIndex,
) -> Self::Tracked<T> {
WithDepNode::new(dep_node, data)
}
fn get_tracked<T: fmt::Debug + Clone>(self, tracked: &Self::Tracked<T>) -> T {
tracked.get(self)
}
fn evaluation_cache(self, mode: SolverMode) -> &'tcx solve::EvaluationCache<'tcx> {
fn with_global_cache<R>(
self,
mode: SolverMode,
f: impl FnOnce(&mut search_graph::GlobalCache<Self>) -> R,
) -> R {
match mode {
SolverMode::Normal => &self.new_solver_evaluation_cache,
SolverMode::Coherence => &self.new_solver_coherence_evaluation_cache,
SolverMode::Normal => f(&mut *self.new_solver_evaluation_cache.lock()),
SolverMode::Coherence => f(&mut *self.new_solver_coherence_evaluation_cache.lock()),
}
}
@ -1283,8 +1298,8 @@ pub struct GlobalCtxt<'tcx> {
pub evaluation_cache: traits::EvaluationCache<'tcx>,
/// Caches the results of goal evaluation in the new solver.
pub new_solver_evaluation_cache: solve::EvaluationCache<'tcx>,
pub new_solver_coherence_evaluation_cache: solve::EvaluationCache<'tcx>,
pub new_solver_evaluation_cache: Lock<search_graph::GlobalCache<TyCtxt<'tcx>>>,
pub new_solver_coherence_evaluation_cache: Lock<search_graph::GlobalCache<TyCtxt<'tcx>>>,
pub canonical_param_env_cache: CanonicalParamEnvCache<'tcx>,

14
compiler/rustc_next_trait_solver/src/solve/eval_ctxt/mod.rs
View File

@ -16,9 +16,9 @@ use crate::delegate::SolverDelegate;
use crate::solve::inspect::{self, ProofTreeBuilder};
use crate::solve::search_graph::SearchGraph;
use crate::solve::{
search_graph, CanonicalInput, CanonicalResponse, Certainty, Goal, GoalEvaluationKind,
GoalSource, MaybeCause, NestedNormalizationGoals, NoSolution, PredefinedOpaquesData,
QueryResult, SolverMode, FIXPOINT_STEP_LIMIT,
CanonicalInput, CanonicalResponse, Certainty, Goal, GoalEvaluationKind, GoalSource, MaybeCause,
NestedNormalizationGoals, NoSolution, PredefinedOpaquesData, QueryResult, SolverMode,
FIXPOINT_STEP_LIMIT,
};
pub(super) mod canonical;
@ -72,7 +72,7 @@ where
/// new placeholders to the caller.
pub(super) max_input_universe: ty::UniverseIndex,
pub(super) search_graph: &'a mut SearchGraph<I>,
pub(super) search_graph: &'a mut SearchGraph<D>,
nested_goals: NestedGoals<I>,
@ -200,7 +200,7 @@ where
generate_proof_tree: GenerateProofTree,
f: impl FnOnce(&mut EvalCtxt<'_, D>) -> R,
) -> (R, Option<inspect::GoalEvaluation<I>>) {
let mut search_graph = search_graph::SearchGraph::new(delegate.solver_mode());
let mut search_graph = SearchGraph::new(delegate.solver_mode());
let mut ecx = EvalCtxt {
delegate,
@ -241,7 +241,7 @@ where
/// and registering opaques from the canonicalized input.
fn enter_canonical<R>(
cx: I,
search_graph: &'a mut search_graph::SearchGraph<I>,
search_graph: &'a mut SearchGraph<D>,
canonical_input: CanonicalInput<I>,
canonical_goal_evaluation: &mut ProofTreeBuilder<D>,
f: impl FnOnce(&mut EvalCtxt<'_, D>, Goal<I, I::Predicate>) -> R,
@ -296,7 +296,7 @@ where
#[instrument(level = "debug", skip(cx, search_graph, goal_evaluation), ret)]
fn evaluate_canonical_goal(
cx: I,
search_graph: &'a mut search_graph::SearchGraph<I>,
search_graph: &'a mut SearchGraph<D>,
canonical_input: CanonicalInput<I>,
goal_evaluation: &mut ProofTreeBuilder<D>,
) -> QueryResult<I> {

69
compiler/rustc_next_trait_solver/src/solve/inspect/build.rs
View File

@ -8,7 +8,7 @@ use std::marker::PhantomData;
use std::mem;
use rustc_type_ir::inherent::*;
use rustc_type_ir::{self as ty, Interner};
use rustc_type_ir::{self as ty, search_graph, Interner};
use crate::delegate::SolverDelegate;
use crate::solve::eval_ctxt::canonical;
@ -38,7 +38,7 @@ use crate::solve::{
/// trees. At the end of trait solving `ProofTreeBuilder::finalize`
/// is called to recursively convert the whole structure to a
/// finished proof tree.
pub(in crate::solve) struct ProofTreeBuilder<D, I = <D as SolverDelegate>::Interner>
pub(crate) struct ProofTreeBuilder<D, I = <D as SolverDelegate>::Interner>
where
D: SolverDelegate<Interner = I>,
I: Interner,
@ -321,23 +321,6 @@ impl<D: SolverDelegate<Interner = I>, I: Interner> ProofTreeBuilder<D> {
})
}
pub fn finalize_canonical_goal_evaluation(
&mut self,
cx: I,
) -> Option<I::CanonicalGoalEvaluationStepRef> {
self.as_mut().map(|this| match this {
DebugSolver::CanonicalGoalEvaluation(evaluation) => {
let final_revision = mem::take(&mut evaluation.final_revision).unwrap();
let final_revision =
cx.intern_canonical_goal_evaluation_step(final_revision.finalize());
let kind = WipCanonicalGoalEvaluationKind::Interned { final_revision };
assert_eq!(evaluation.kind.replace(kind), None);
final_revision
}
_ => unreachable!(),
})
}
pub fn canonical_goal_evaluation(&mut self, canonical_goal_evaluation: ProofTreeBuilder<D>) {
if let Some(this) = self.as_mut() {
match (this, *canonical_goal_evaluation.state.unwrap()) {
@ -571,3 +554,51 @@ impl<D: SolverDelegate<Interner = I>, I: Interner> ProofTreeBuilder<D> {
}
}
}
impl<D, I> search_graph::ProofTreeBuilder<I> for ProofTreeBuilder<D>
where
D: SolverDelegate<Interner = I>,
I: Interner,
{
fn try_apply_proof_tree(
&mut self,
proof_tree: Option<I::CanonicalGoalEvaluationStepRef>,
) -> bool {
if !self.is_noop() {
if let Some(final_revision) = proof_tree {
let kind = WipCanonicalGoalEvaluationKind::Interned { final_revision };
self.canonical_goal_evaluation_kind(kind);
true
} else {
false
}
} else {
true
}
}
fn on_provisional_cache_hit(&mut self) {
self.canonical_goal_evaluation_kind(WipCanonicalGoalEvaluationKind::ProvisionalCacheHit);
}
fn on_cycle_in_stack(&mut self) {
self.canonical_goal_evaluation_kind(WipCanonicalGoalEvaluationKind::CycleInStack);
}
fn finalize_canonical_goal_evaluation(
&mut self,
tcx: I,
) -> Option<I::CanonicalGoalEvaluationStepRef> {
self.as_mut().map(|this| match this {
DebugSolver::CanonicalGoalEvaluation(evaluation) => {
let final_revision = mem::take(&mut evaluation.final_revision).unwrap();
let final_revision =
tcx.intern_canonical_goal_evaluation_step(final_revision.finalize());
let kind = WipCanonicalGoalEvaluationKind::Interned { final_revision };
assert_eq!(evaluation.kind.replace(kind), None);
final_revision
}
_ => unreachable!(),
})
}
}

631
compiler/rustc_next_trait_solver/src/solve/search_graph.rs
View File

@ -1,599 +1,90 @@
use std::mem;
use std::marker::PhantomData;
use rustc_index::{Idx, IndexVec};
use rustc_type_ir::data_structures::{HashMap, HashSet};
use rustc_type_ir::inherent::*;
use rustc_type_ir::search_graph::{self, CycleKind, UsageKind};
use rustc_type_ir::solve::{CanonicalInput, Certainty, QueryResult};
use rustc_type_ir::Interner;
use tracing::debug;
use super::inspect::{self, ProofTreeBuilder};
use super::FIXPOINT_STEP_LIMIT;
use crate::delegate::SolverDelegate;
use crate::solve::inspect::{self, ProofTreeBuilder};
use crate::solve::{
CacheData, CanonicalInput, Certainty, QueryResult, SolverMode, FIXPOINT_STEP_LIMIT,
};
#[derive(Copy, Clone, PartialEq, Eq, Debug)]
pub struct SolverLimit(usize);
rustc_index::newtype_index! {
#[orderable]
#[gate_rustc_only]
pub struct StackDepth {}
/// This type is never constructed. We only use it to implement `search_graph::Delegate`
/// for all types which impl `SolverDelegate` and doing it directly fails in coherence.
pub(super) struct SearchGraphDelegate<D: SolverDelegate> {
_marker: PhantomData<D>,
}
pub(super) type SearchGraph<D> = search_graph::SearchGraph<SearchGraphDelegate<D>>;
impl<D, I> search_graph::Delegate for SearchGraphDelegate<D>
where
D: SolverDelegate<Interner = I>,
I: Interner,
{
type Cx = D::Interner;
bitflags::bitflags! {
/// Whether and how this goal has been used as the root of a
/// cycle. We track the kind of cycle as we're otherwise forced
/// to always rerun at least once.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
struct HasBeenUsed: u8 {
const INDUCTIVE_CYCLE = 1 << 0;
const COINDUCTIVE_CYCLE = 1 << 1;
}
}
const FIXPOINT_STEP_LIMIT: usize = FIXPOINT_STEP_LIMIT;
#[derive(derivative::Derivative)]
#[derivative(Debug(bound = ""))]
struct StackEntry<I: Interner> {
input: CanonicalInput<I>,
type ProofTreeBuilder = ProofTreeBuilder<D>;
available_depth: SolverLimit,
/// The maximum depth reached by this stack entry, only up-to date
/// for the top of the stack and lazily updated for the rest.
reached_depth: StackDepth,
/// Whether this entry is a non-root cycle participant.
///
/// We must not move the result of non-root cycle participants to the
/// global cache. We store the highest stack depth of a head of a cycle
/// this goal is involved in. This necessary to soundly cache its
/// provisional result.
non_root_cycle_participant: Option<StackDepth>,
encountered_overflow: bool,
has_been_used: HasBeenUsed,
/// We put only the root goal of a coinductive cycle into the global cache.
///
/// If we were to use that result when later trying to prove another cycle
/// participant, we can end up with unstable query results.
///
/// See tests/ui/next-solver/coinduction/incompleteness-unstable-result.rs for
/// an example of where this is needed.
///
/// There can be multiple roots on the same stack, so we need to track
/// cycle participants per root:
/// ```plain
/// A :- B
/// B :- A, C
/// C :- D
/// D :- C
/// ```
nested_goals: HashSet<CanonicalInput<I>>,
/// Starts out as `None` and gets set when rerunning this
/// goal in case we encounter a cycle.
provisional_result: Option<QueryResult<I>>,
}
/// The provisional result for a goal which is not on the stack.
#[derive(Debug)]
struct DetachedEntry<I: Interner> {
/// The head of the smallest non-trivial cycle involving this entry.
///
/// Given the following rules, when proving `A` the head for
/// the provisional entry of `C` would be `B`.
/// ```plain
/// A :- B
/// B :- C
/// C :- A + B + C
/// ```
head: StackDepth,
result: QueryResult<I>,
}
/// Stores the stack depth of a currently evaluated goal *and* already
/// computed results for goals which depend on other goals still on the stack.
///
/// The provisional result may depend on whether the stack above it is inductive
/// or coinductive. Because of this, we store separate provisional results for
/// each case. If an provisional entry is not applicable, it may be the case
/// that we already have provisional result while computing a goal. In this case
/// we prefer the provisional result to potentially avoid fixpoint iterations.
/// See tests/ui/traits/next-solver/cycles/mixed-cycles-2.rs for an example.
///
/// The provisional cache can theoretically result in changes to the observable behavior,
/// see tests/ui/traits/next-solver/cycles/provisional-cache-impacts-behavior.rs.
#[derive(derivative::Derivative)]
#[derivative(Default(bound = ""))]
struct ProvisionalCacheEntry<I: Interner> {
stack_depth: Option<StackDepth>,
with_inductive_stack: Option<DetachedEntry<I>>,
with_coinductive_stack: Option<DetachedEntry<I>>,
}
impl<I: Interner> ProvisionalCacheEntry<I> {
fn is_empty(&self) -> bool {
self.stack_depth.is_none()
&& self.with_inductive_stack.is_none()
&& self.with_coinductive_stack.is_none()
}
}
pub(super) struct SearchGraph<I: Interner> {
mode: SolverMode,
/// The stack of goals currently being computed.
///
/// An element is *deeper* in the stack if its index is *lower*.
stack: IndexVec<StackDepth, StackEntry<I>>,
provisional_cache: HashMap<CanonicalInput<I>, ProvisionalCacheEntry<I>>,
}
impl<I: Interner> SearchGraph<I> {
pub(super) fn new(mode: SolverMode) -> SearchGraph<I> {
Self { mode, stack: Default::default(), provisional_cache: Default::default() }
fn recursion_limit(cx: I) -> usize {
cx.recursion_limit()
}
pub(super) fn solver_mode(&self) -> SolverMode {
self.mode
}
fn update_parent_goal(&mut self, reached_depth: StackDepth, encountered_overflow: bool) {
if let Some(parent) = self.stack.raw.last_mut() {
parent.reached_depth = parent.reached_depth.max(reached_depth);
parent.encountered_overflow |= encountered_overflow;
fn initial_provisional_result(
cx: I,
kind: CycleKind,
input: CanonicalInput<I>,
) -> QueryResult<I> {
match kind {
CycleKind::Coinductive => response_no_constraints(cx, input, Certainty::Yes),
CycleKind::Inductive => response_no_constraints(cx, input, Certainty::overflow(false)),
}
}
pub(super) fn is_empty(&self) -> bool {
self.stack.is_empty()
}
/// Returns the remaining depth allowed for nested goals.
///
/// This is generally simply one less than the current depth.
/// However, if we encountered overflow, we significantly reduce
/// the remaining depth of all nested goals to prevent hangs
/// in case there is exponential blowup.
fn allowed_depth_for_nested(
fn reached_fixpoint(
cx: I,
stack: &IndexVec<StackDepth, StackEntry<I>>,
) -> Option<SolverLimit> {
if let Some(last) = stack.raw.last() {
if last.available_depth.0 == 0 {
return None;
}
Some(if last.encountered_overflow {
SolverLimit(last.available_depth.0 / 4)
} else {
SolverLimit(last.available_depth.0 - 1)
})
} else {
Some(SolverLimit(cx.recursion_limit()))
}
}
fn stack_coinductive_from(
cx: I,
stack: &IndexVec<StackDepth, StackEntry<I>>,
head: StackDepth,
kind: UsageKind,
input: CanonicalInput<I>,
provisional_result: Option<QueryResult<I>>,
result: QueryResult<I>,
) -> bool {
stack.raw[head.index()..]
.iter()
.all(|entry| entry.input.value.goal.predicate.is_coinductive(cx))
}
// When encountering a solver cycle, the result of the current goal
// depends on goals lower on the stack.
//
// We have to therefore be careful when caching goals. Only the final result
// of the cycle root, i.e. the lowest goal on the stack involved in this cycle,
// is moved to the global cache while all others are stored in a provisional cache.
//
// We update both the head of this cycle to rerun its evaluation until
// we reach a fixpoint and all other cycle participants to make sure that
// their result does not get moved to the global cache.
fn tag_cycle_participants(
stack: &mut IndexVec<StackDepth, StackEntry<I>>,
usage_kind: HasBeenUsed,
head: StackDepth,
) {
stack[head].has_been_used |= usage_kind;
debug_assert!(!stack[head].has_been_used.is_empty());
// The current root of these cycles. Note that this may not be the final
// root in case a later goal depends on a goal higher up the stack.
let mut current_root = head;
while let Some(parent) = stack[current_root].non_root_cycle_participant {
current_root = parent;
debug_assert!(!stack[current_root].has_been_used.is_empty());
}
let (stack, cycle_participants) = stack.raw.split_at_mut(head.index() + 1);
let current_cycle_root = &mut stack[current_root.as_usize()];
for entry in cycle_participants {
entry.non_root_cycle_participant = entry.non_root_cycle_participant.max(Some(head));
current_cycle_root.nested_goals.insert(entry.input);
current_cycle_root.nested_goals.extend(mem::take(&mut entry.nested_goals));
}
}
fn clear_dependent_provisional_results(
provisional_cache: &mut HashMap<CanonicalInput<I>, ProvisionalCacheEntry<I>>,
head: StackDepth,
) {
#[allow(rustc::potential_query_instability)]
provisional_cache.retain(|_, entry| {
if entry.with_coinductive_stack.as_ref().is_some_and(|p| p.head == head) {
entry.with_coinductive_stack.take();
}
if entry.with_inductive_stack.as_ref().is_some_and(|p| p.head == head) {
entry.with_inductive_stack.take();
}
!entry.is_empty()
});
}
/// The trait solver behavior is different for coherence
/// so we use a separate cache. Alternatively we could use
/// a single cache and share it between coherence and ordinary
/// trait solving.
pub(super) fn global_cache(&self, cx: I) -> I::EvaluationCache {
cx.evaluation_cache(self.mode)
}
/// Probably the most involved method of the whole solver.
///
/// Given some goal which is proven via the `prove_goal` closure, this
/// handles caching, overflow, and coinductive cycles.
pub(super) fn with_new_goal<D: SolverDelegate<Interner = I>>(
&mut self,
cx: I,
input: CanonicalInput<I>,
inspect: &mut ProofTreeBuilder<D>,
mut prove_goal: impl FnMut(&mut Self, &mut ProofTreeBuilder<D>) -> QueryResult<I>,
) -> QueryResult<I> {
self.check_invariants();
// Check for overflow.
let Some(available_depth) = Self::allowed_depth_for_nested(cx, &self.stack) else {
if let Some(last) = self.stack.raw.last_mut() {
last.encountered_overflow = true;
}
inspect
.canonical_goal_evaluation_kind(inspect::WipCanonicalGoalEvaluationKind::Overflow);
return Self::response_no_constraints(cx, input, Certainty::overflow(true));
};
if let Some(result) = self.lookup_global_cache(cx, input, available_depth, inspect) {
debug!("global cache hit");
return result;
}
// Check whether the goal is in the provisional cache.
// The provisional result may rely on the path to its cycle roots,
// so we have to check the path of the current goal matches that of
// the cache entry.
let cache_entry = self.provisional_cache.entry(input).or_default();
if let Some(entry) = cache_entry
.with_coinductive_stack
.as_ref()
.filter(|p| Self::stack_coinductive_from(cx, &self.stack, p.head))
.or_else(|| {
cache_entry
.with_inductive_stack
.as_ref()
.filter(|p| !Self::stack_coinductive_from(cx, &self.stack, p.head))
})
{
debug!("provisional cache hit");
// We have a nested goal which is already in the provisional cache, use
// its result. We do not provide any usage kind as that should have been
// already set correctly while computing the cache entry.
inspect.canonical_goal_evaluation_kind(
inspect::WipCanonicalGoalEvaluationKind::ProvisionalCacheHit,
);
Self::tag_cycle_participants(&mut self.stack, HasBeenUsed::empty(), entry.head);
return entry.result;
} else if let Some(stack_depth) = cache_entry.stack_depth {
debug!("encountered cycle with depth {stack_depth:?}");
// We have a nested goal which directly relies on a goal deeper in the stack.
//
// We start by tagging all cycle participants, as that's necessary for caching.
//
// Finally we can return either the provisional response or the initial response
// in case we're in the first fixpoint iteration for this goal.
inspect.canonical_goal_evaluation_kind(
inspect::WipCanonicalGoalEvaluationKind::CycleInStack,
);
let is_coinductive_cycle = Self::stack_coinductive_from(cx, &self.stack, stack_depth);
let usage_kind = if is_coinductive_cycle {
HasBeenUsed::COINDUCTIVE_CYCLE
} else {
HasBeenUsed::INDUCTIVE_CYCLE
};
Self::tag_cycle_participants(&mut self.stack, usage_kind, stack_depth);
// Return the provisional result or, if we're in the first iteration,
// start with no constraints.
return if let Some(result) = self.stack[stack_depth].provisional_result {
result
} else if is_coinductive_cycle {
Self::response_no_constraints(cx, input, Certainty::Yes)
} else {
Self::response_no_constraints(cx, input, Certainty::overflow(false))
};
} else {
// No entry, we push this goal on the stack and try to prove it.
let depth = self.stack.next_index();
let entry = StackEntry {
input,
available_depth,
reached_depth: depth,
non_root_cycle_participant: None,
encountered_overflow: false,
has_been_used: HasBeenUsed::empty(),
nested_goals: Default::default(),
provisional_result: None,
};
assert_eq!(self.stack.push(entry), depth);
cache_entry.stack_depth = Some(depth);
}
// This is for global caching, so we properly track query dependencies.
// Everything that affects the `result` should be performed within this
// `with_anon_task` closure. If computing this goal depends on something
// not tracked by the cache key and from outside of this anon task, it
// must not be added to the global cache. Notably, this is the case for
// trait solver cycles participants.
let ((final_entry, result), dep_node) = cx.with_cached_task(|| {
for _ in 0..FIXPOINT_STEP_LIMIT {
match self.fixpoint_step_in_task(cx, input, inspect, &mut prove_goal) {
StepResult::Done(final_entry, result) => return (final_entry, result),
StepResult::HasChanged => debug!("fixpoint changed provisional results"),
}
}
debug!("canonical cycle overflow");
let current_entry = self.stack.pop().unwrap();
debug_assert!(current_entry.has_been_used.is_empty());
let result = Self::response_no_constraints(cx, input, Certainty::overflow(false));
(current_entry, result)
});
let proof_tree = inspect.finalize_canonical_goal_evaluation(cx);
self.update_parent_goal(final_entry.reached_depth, final_entry.encountered_overflow);
// We're now done with this goal. In case this goal is involved in a larger cycle
// do not remove it from the provisional cache and update its provisional result.
// We only add the root of cycles to the global cache.
if let Some(head) = final_entry.non_root_cycle_participant {
let coinductive_stack = Self::stack_coinductive_from(cx, &self.stack, head);
let entry = self.provisional_cache.get_mut(&input).unwrap();
entry.stack_depth = None;
if coinductive_stack {
entry.with_coinductive_stack = Some(DetachedEntry { head, result });
} else {
entry.with_inductive_stack = Some(DetachedEntry { head, result });
}
} else {
self.provisional_cache.remove(&input);
let reached_depth = final_entry.reached_depth.as_usize() - self.stack.len();
// When encountering a cycle, both inductive and coinductive, we only
// move the root into the global cache. We also store all other cycle
// participants involved.
//
// We must not use the global cache entry of a root goal if a cycle
// participant is on the stack. This is necessary to prevent unstable
// results. See the comment of `StackEntry::nested_goals` for
// more details.
self.global_cache(cx).insert(
cx,
input,
proof_tree,
reached_depth,
final_entry.encountered_overflow,
final_entry.nested_goals,
dep_node,
result,
)
}
self.check_invariants();
result
}
/// Try to fetch a previously computed result from the global cache,
/// making sure to only do so if it would match the result of reevaluating
/// this goal.
fn lookup_global_cache<D: SolverDelegate<Interner = I>>(
&mut self,
cx: I,
input: CanonicalInput<I>,
available_depth: SolverLimit,
inspect: &mut ProofTreeBuilder<D>,
) -> Option<QueryResult<I>> {
let CacheData { result, proof_tree, additional_depth, encountered_overflow } = self
.global_cache(cx)
// FIXME: Awkward `Limit -> usize -> Limit`.
.get(cx, input, self.stack.iter().map(|e| e.input), available_depth.0)?;
// If we're building a proof tree and the current cache entry does not
// contain a proof tree, we do not use the entry but instead recompute
// the goal. We simply overwrite the existing entry once we're done,
// caching the proof tree.
if !inspect.is_noop() {
if let Some(final_revision) = proof_tree {
let kind = inspect::WipCanonicalGoalEvaluationKind::Interned { final_revision };
inspect.canonical_goal_evaluation_kind(kind);
} else {
return None;
}
}
// Adjust the parent goal as if we actually computed this goal.
let reached_depth = self.stack.next_index().plus(additional_depth);
self.update_parent_goal(reached_depth, encountered_overflow);
Some(result)
}
}
enum StepResult<I: Interner> {
Done(StackEntry<I>, QueryResult<I>),
HasChanged,
}
impl<I: Interner> SearchGraph<I> {
/// When we encounter a coinductive cycle, we have to fetch the
/// result of that cycle while we are still computing it. Because
/// of this we continuously recompute the cycle until the result
/// of the previous iteration is equal to the final result, at which
/// point we are done.
fn fixpoint_step_in_task<D, F>(
&mut self,
cx: I,
input: CanonicalInput<I>,
inspect: &mut ProofTreeBuilder<D>,
prove_goal: &mut F,
) -> StepResult<I>
where
D: SolverDelegate<Interner = I>,
F: FnMut(&mut Self, &mut ProofTreeBuilder<D>) -> QueryResult<I>,
{
let result = prove_goal(self, inspect);
let stack_entry = self.stack.pop().unwrap();
debug_assert_eq!(stack_entry.input, input);
// If the current goal is not the root of a cycle, we are done.
if stack_entry.has_been_used.is_empty() {
return StepResult::Done(stack_entry, result);
}
// If it is a cycle head, we have to keep trying to prove it until
// we reach a fixpoint. We need to do so for all cycle heads,
// not only for the root.
//
// See tests/ui/traits/next-solver/cycles/fixpoint-rerun-all-cycle-heads.rs
// for an example.
// Start by clearing all provisional cache entries which depend on this
// the current goal.
Self::clear_dependent_provisional_results(
&mut self.provisional_cache,
self.stack.next_index(),
);
// Check whether we reached a fixpoint, either because the final result
// is equal to the provisional result of the previous iteration, or because
// this was only the root of either coinductive or inductive cycles, and the
// final result is equal to the initial response for that case.
let reached_fixpoint = if let Some(r) = stack_entry.provisional_result {
if let Some(r) = provisional_result {
r == result
} else if stack_entry.has_been_used == HasBeenUsed::COINDUCTIVE_CYCLE {
Self::response_no_constraints(cx, input, Certainty::Yes) == result
} else if stack_entry.has_been_used == HasBeenUsed::INDUCTIVE_CYCLE {
Self::response_no_constraints(cx, input, Certainty::overflow(false)) == result
} else {
false
};
// If we did not reach a fixpoint, update the provisional result and reevaluate.
if reached_fixpoint {
StepResult::Done(stack_entry, result)
} else {
let depth = self.stack.push(StackEntry {
has_been_used: HasBeenUsed::empty(),
provisional_result: Some(result),
..stack_entry
});
debug_assert_eq!(self.provisional_cache[&input].stack_depth, Some(depth));
StepResult::HasChanged
match kind {
UsageKind::Single(CycleKind::Coinductive) => {
response_no_constraints(cx, input, Certainty::Yes) == result
}
UsageKind::Single(CycleKind::Inductive) => {
response_no_constraints(cx, input, Certainty::overflow(false)) == result
}
UsageKind::Mixed => false,
}
}
}
fn response_no_constraints(
fn on_stack_overflow(
cx: I,
goal: CanonicalInput<I>,
certainty: Certainty,
inspect: &mut ProofTreeBuilder<D>,
input: CanonicalInput<I>,
) -> QueryResult<I> {
Ok(super::response_no_constraints_raw(cx, goal.max_universe, goal.variables, certainty))
inspect.canonical_goal_evaluation_kind(inspect::WipCanonicalGoalEvaluationKind::Overflow);
response_no_constraints(cx, input, Certainty::overflow(true))
}
#[allow(rustc::potential_query_instability)]
fn check_invariants(&self) {
if !cfg!(debug_assertions) {
return;
}
fn on_fixpoint_overflow(cx: I, input: CanonicalInput<I>) -> QueryResult<I> {
response_no_constraints(cx, input, Certainty::overflow(false))
}
let SearchGraph { mode: _, stack, provisional_cache } = self;
if stack.is_empty() {
assert!(provisional_cache.is_empty());
}
for (depth, entry) in stack.iter_enumerated() {
let StackEntry {
input,
available_depth: _,
reached_depth: _,
non_root_cycle_participant,
encountered_overflow: _,
has_been_used,
ref nested_goals,
provisional_result,
} = *entry;
let cache_entry = provisional_cache.get(&entry.input).unwrap();
assert_eq!(cache_entry.stack_depth, Some(depth));
if let Some(head) = non_root_cycle_participant {
assert!(head < depth);
assert!(nested_goals.is_empty());
assert_ne!(stack[head].has_been_used, HasBeenUsed::empty());
let mut current_root = head;
while let Some(parent) = stack[current_root].non_root_cycle_participant {
current_root = parent;
}
assert!(stack[current_root].nested_goals.contains(&input));
}
if !nested_goals.is_empty() {
assert!(provisional_result.is_some() || !has_been_used.is_empty());
for entry in stack.iter().take(depth.as_usize()) {
assert_eq!(nested_goals.get(&entry.input), None);
}
}
}
for (&input, entry) in &self.provisional_cache {
let ProvisionalCacheEntry { stack_depth, with_coinductive_stack, with_inductive_stack } =
entry;
assert!(
stack_depth.is_some()
|| with_coinductive_stack.is_some()
|| with_inductive_stack.is_some()
);
if let &Some(stack_depth) = stack_depth {
assert_eq!(stack[stack_depth].input, input);
}
let check_detached = |detached_entry: &DetachedEntry<I>| {
let DetachedEntry { head, result: _ } = *detached_entry;
assert_ne!(stack[head].has_been_used, HasBeenUsed::empty());
};
if let Some(with_coinductive_stack) = with_coinductive_stack {
check_detached(with_coinductive_stack);
}
if let Some(with_inductive_stack) = with_inductive_stack {
check_detached(with_inductive_stack);
}
}
fn step_is_coinductive(cx: I, input: CanonicalInput<I>) -> bool {
input.value.goal.predicate.is_coinductive(cx)
}
}
fn response_no_constraints<I: Interner>(
cx: I,
goal: CanonicalInput<I>,
certainty: Certainty,
) -> QueryResult<I> {
Ok(super::response_no_constraints_raw(cx, goal.max_universe, goal.variables, certainty))
}

2
compiler/rustc_query_system/src/cache.rs
View File

@ -40,7 +40,7 @@ impl<Key: Eq + Hash, Value: Clone> Cache<Key, Value> {
}
}
#[derive(Clone, Eq, PartialEq)]
#[derive(Debug, Clone, Eq, PartialEq)]
pub struct WithDepNode<T> {
dep_node: DepNodeIndex,
cached_value: T,

30
compiler/rustc_type_ir/src/inherent.rs
View File

@ -8,11 +8,10 @@ use std::hash::Hash;
use rustc_ast_ir::Mutability;
use crate::data_structures::HashSet;
use crate::elaborate::Elaboratable;
use crate::fold::{TypeFoldable, TypeSuperFoldable};
use crate::relate::Relate;
use crate::solve::{CacheData, CanonicalInput, QueryResult, Reveal};
use crate::solve::Reveal;
use crate::visit::{Flags, TypeSuperVisitable, TypeVisitable};
use crate::{self as ty, CollectAndApply, Interner, UpcastFrom};
@ -539,33 +538,6 @@ pub trait Features<I: Interner>: Copy {
fn associated_const_equality(self) -> bool;
}
pub trait EvaluationCache<I: Interner> {
/// Insert a final result into the global cache.
fn insert(
&self,
tcx: I,
key: CanonicalInput<I>,
proof_tree: Option<I::CanonicalGoalEvaluationStepRef>,
additional_depth: usize,
encountered_overflow: bool,
cycle_participants: HashSet<CanonicalInput<I>>,
dep_node: I::DepNodeIndex,
result: QueryResult<I>,
);
/// Try to fetch a cached result, checking the recursion limit
/// and handling root goals of coinductive cycles.
///
/// If this returns `Some` the cache result can be used.
fn get(
&self,
tcx: I,
key: CanonicalInput<I>,
stack_entries: impl IntoIterator<Item = CanonicalInput<I>>,
available_depth: usize,
) -> Option<CacheData<I>>;
}
pub trait DefId<I: Interner>: Copy + Debug + Hash + Eq + TypeFoldable<I> {
fn is_local(self) -> bool;

48
compiler/rustc_type_ir/src/interner.rs
View File

@ -10,8 +10,11 @@ use crate::inherent::*;
use crate::ir_print::IrPrint;
use crate::lang_items::TraitSolverLangItem;
use crate::relate::Relate;
use crate::search_graph;
use crate::solve::inspect::CanonicalGoalEvaluationStep;
use crate::solve::{ExternalConstraintsData, PredefinedOpaquesData, SolverMode};
use crate::solve::{
CanonicalInput, ExternalConstraintsData, PredefinedOpaquesData, QueryResult, SolverMode,
};
use crate::visit::{Flags, TypeSuperVisitable, TypeVisitable};
use crate::{self as ty};
@ -86,6 +89,13 @@ pub trait Interner:
) -> Self::ExternalConstraints;
type DepNodeIndex;
type Tracked<T: Debug + Clone>: Debug;
fn mk_tracked<T: Debug + Clone>(
self,
data: T,
dep_node: Self::DepNodeIndex,
) -> Self::Tracked<T>;
fn get_tracked<T: Debug + Clone>(self, tracked: &Self::Tracked<T>) -> T;
fn with_cached_task<T>(self, task: impl FnOnce() -> T) -> (T, Self::DepNodeIndex);
// Kinds of tys
@ -125,8 +135,11 @@ pub trait Interner:
type Clause: Clause<Self>;
type Clauses: Copy + Debug + Hash + Eq + TypeSuperVisitable<Self> + Flags;
type EvaluationCache: EvaluationCache<Self>;
fn evaluation_cache(self, mode: SolverMode) -> Self::EvaluationCache;
fn with_global_cache<R>(
self,
mode: SolverMode,
f: impl FnOnce(&mut search_graph::GlobalCache<Self>) -> R,
) -> R;
fn expand_abstract_consts<T: TypeFoldable<Self>>(self, t: T) -> T;
@ -373,3 +386,32 @@ impl<T, R, E> CollectAndApply<T, R> for Result<T, E> {
})
}
}
impl<I: Interner> search_graph::Cx for I {
type ProofTree = Option<I::CanonicalGoalEvaluationStepRef>;
type Input = CanonicalInput<I>;
type Result = QueryResult<I>;
type DepNodeIndex = I::DepNodeIndex;
type Tracked<T: Debug + Clone> = I::Tracked<T>;
fn mk_tracked<T: Debug + Clone>(
self,
data: T,
dep_node_index: I::DepNodeIndex,
) -> I::Tracked<T> {
I::mk_tracked(self, data, dep_node_index)
}
fn get_tracked<T: Debug + Clone>(self, tracked: &I::Tracked<T>) -> T {
I::get_tracked(self, tracked)
}
fn with_cached_task<T>(self, task: impl FnOnce() -> T) -> (T, I::DepNodeIndex) {
I::with_cached_task(self, task)
}
fn with_global_cache<R>(
self,
mode: SolverMode,
f: impl FnOnce(&mut search_graph::GlobalCache<Self>) -> R,
) -> R {
I::with_global_cache(self, mode, f)
}
}

1
compiler/rustc_type_ir/src/lib.rs
View File

@ -30,6 +30,7 @@ pub mod lang_items;
pub mod lift;
pub mod outlives;
pub mod relate;
pub mod search_graph;
pub mod solve;
// These modules are not `pub` since they are glob-imported.

118
compiler/rustc_type_ir/src/search_graph/global_cache.rs Normal file
View File

@ -0,0 +1,118 @@
use rustc_index::IndexVec;
use super::{AvailableDepth, Cx, StackDepth, StackEntry};
use crate::data_structures::{HashMap, HashSet};
#[derive(derivative::Derivative)]
#[derivative(Debug(bound = ""), Clone(bound = ""), Copy(bound = ""))]
struct QueryData<X: Cx> {
result: X::Result,
proof_tree: X::ProofTree,
}
struct Success<X: Cx> {
data: X::Tracked<QueryData<X>>,
additional_depth: usize,
}
/// The cache entry for a given input.
///
/// This contains results whose computation never hit the
/// recursion limit in `success`, and all results which hit
/// the recursion limit in `with_overflow`.
#[derive(derivative::Derivative)]
#[derivative(Default(bound = ""))]
struct CacheEntry<X: Cx> {
success: Option<Success<X>>,
/// We have to be careful when caching roots of cycles.
///
/// See the doc comment of `StackEntry::cycle_participants` for more
/// details.
nested_goals: HashSet<X::Input>,
with_overflow: HashMap<usize, X::Tracked<QueryData<X>>>,
}
#[derive(derivative::Derivative)]
#[derivative(Debug(bound = ""))]
pub(super) struct CacheData<'a, X: Cx> {
pub(super) result: X::Result,
pub(super) proof_tree: X::ProofTree,
pub(super) additional_depth: usize,
pub(super) encountered_overflow: bool,
// FIXME: This is currently unused, but impacts the design
// by requiring a closure for `Cx::with_global_cache`.
pub(super) nested_goals: &'a HashSet<X::Input>,
}
#[derive(derivative::Derivative)]
#[derivative(Default(bound = ""))]
pub struct GlobalCache<X: Cx> {
map: HashMap<X::Input, CacheEntry<X>>,
}
impl<X: Cx> GlobalCache<X> {
/// Insert a final result into the global cache.
pub(super) fn insert(
&mut self,
cx: X,
input: X::Input,
result: X::Result,
proof_tree: X::ProofTree,
dep_node: X::DepNodeIndex,
additional_depth: usize,
encountered_overflow: bool,
nested_goals: &HashSet<X::Input>,
) {
let data = cx.mk_tracked(QueryData { result, proof_tree }, dep_node);
let entry = self.map.entry(input).or_default();
entry.nested_goals.extend(nested_goals);
if encountered_overflow {
entry.with_overflow.insert(additional_depth, data);
} else {
entry.success = Some(Success { data, additional_depth });
}
}
/// Try to fetch a cached result, checking the recursion limit
/// and handling root goals of coinductive cycles.
///
/// If this returns `Some` the cache result can be used.
pub(super) fn get<'a>(
&'a self,
cx: X,
input: X::Input,
stack: &IndexVec<StackDepth, StackEntry<X>>,
available_depth: AvailableDepth,
) -> Option<CacheData<'a, X>> {
let entry = self.map.get(&input)?;
if stack.iter().any(|e| entry.nested_goals.contains(&e.input)) {
return None;
}
if let Some(ref success) = entry.success {
if available_depth.cache_entry_is_applicable(success.additional_depth) {
let QueryData { result, proof_tree } = cx.get_tracked(&success.data);
return Some(CacheData {
result,
proof_tree,
additional_depth: success.additional_depth,
encountered_overflow: false,
nested_goals: &entry.nested_goals,
});
}
}
entry.with_overflow.get(&available_depth.0).map(|e| {
let QueryData { result, proof_tree } = cx.get_tracked(e);
CacheData {
result,
proof_tree,
additional_depth: available_depth.0,
encountered_overflow: true,
nested_goals: &entry.nested_goals,
}
})
}
}

605
compiler/rustc_type_ir/src/search_graph/mod.rs Normal file
View File

@ -0,0 +1,605 @@
use std::fmt::Debug;
use std::hash::Hash;
use std::marker::PhantomData;
use std::mem;
use rustc_index::{Idx, IndexVec};
use tracing::debug;
use crate::data_structures::{HashMap, HashSet};
use crate::solve::SolverMode;
mod global_cache;
use global_cache::CacheData;
pub use global_cache::GlobalCache;
mod validate;
/// The search graph does not simply use `Interner` directly
/// to enable its fuzzing without having to stub the rest of
/// the interner. We don't make this a super trait of `Interner`
/// as users of the shared type library shouldn't have to care
/// about `Input` and `Result` as they are implementation details
/// of the search graph.
pub trait Cx: Copy {
type ProofTree: Debug + Copy;
type Input: Debug + Eq + Hash + Copy;
type Result: Debug + Eq + Hash + Copy;
type DepNodeIndex;
type Tracked<T: Debug + Clone>: Debug;
fn mk_tracked<T: Debug + Clone>(
self,
data: T,
dep_node_index: Self::DepNodeIndex,
) -> Self::Tracked<T>;
fn get_tracked<T: Debug + Clone>(self, tracked: &Self::Tracked<T>) -> T;
fn with_cached_task<T>(self, task: impl FnOnce() -> T) -> (T, Self::DepNodeIndex);
fn with_global_cache<R>(
self,
mode: SolverMode,
f: impl FnOnce(&mut GlobalCache<Self>) -> R,
) -> R;
}
pub trait ProofTreeBuilder<X: Cx> {
fn try_apply_proof_tree(&mut self, proof_tree: X::ProofTree) -> bool;
fn on_provisional_cache_hit(&mut self);
fn on_cycle_in_stack(&mut self);
fn finalize_canonical_goal_evaluation(&mut self, cx: X) -> X::ProofTree;
}
pub trait Delegate {
type Cx: Cx;
const FIXPOINT_STEP_LIMIT: usize;
type ProofTreeBuilder: ProofTreeBuilder<Self::Cx>;
fn recursion_limit(cx: Self::Cx) -> usize;
fn initial_provisional_result(
cx: Self::Cx,
kind: CycleKind,
input: <Self::Cx as Cx>::Input,
) -> <Self::Cx as Cx>::Result;
fn reached_fixpoint(
cx: Self::Cx,
kind: UsageKind,
input: <Self::Cx as Cx>::Input,
provisional_result: Option<<Self::Cx as Cx>::Result>,
result: <Self::Cx as Cx>::Result,
) -> bool;
fn on_stack_overflow(
cx: Self::Cx,
inspect: &mut Self::ProofTreeBuilder,
input: <Self::Cx as Cx>::Input,
) -> <Self::Cx as Cx>::Result;
fn on_fixpoint_overflow(
cx: Self::Cx,
input: <Self::Cx as Cx>::Input,
) -> <Self::Cx as Cx>::Result;
fn step_is_coinductive(cx: Self::Cx, input: <Self::Cx as Cx>::Input) -> bool;
}
/// In the initial iteration of a cycle, we do not yet have a provisional
/// result. In the case we return an initial provisional result depending
/// on the kind of cycle.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum CycleKind {
Coinductive,
Inductive,
}
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum UsageKind {
Single(CycleKind),
Mixed,
}
impl UsageKind {
fn merge(self, other: Self) -> Self {
match (self, other) {
(UsageKind::Single(lhs), UsageKind::Single(rhs)) => {
if lhs == rhs {
UsageKind::Single(lhs)
} else {
UsageKind::Mixed
}
}
(UsageKind::Mixed, UsageKind::Mixed)
| (UsageKind::Mixed, UsageKind::Single(_))
| (UsageKind::Single(_), UsageKind::Mixed) => UsageKind::Mixed,
}
}
}
#[derive(Debug, Clone, Copy)]
struct AvailableDepth(usize);
impl AvailableDepth {
/// Returns the remaining depth allowed for nested goals.
///
/// This is generally simply one less than the current depth.
/// However, if we encountered overflow, we significantly reduce
/// the remaining depth of all nested goals to prevent hangs
/// in case there is exponential blowup.
fn allowed_depth_for_nested<D: Delegate>(
cx: D::Cx,
stack: &IndexVec<StackDepth, StackEntry<D::Cx>>,
) -> Option<AvailableDepth> {
if let Some(last) = stack.raw.last() {
if last.available_depth.0 == 0 {
return None;
}
Some(if last.encountered_overflow {
AvailableDepth(last.available_depth.0 / 2)
} else {
AvailableDepth(last.available_depth.0 - 1)
})
} else {
Some(AvailableDepth(D::recursion_limit(cx)))
}
}
/// Whether we're allowed to use a global cache entry which required
/// the given depth.
fn cache_entry_is_applicable(self, additional_depth: usize) -> bool {
self.0 >= additional_depth
}
}
rustc_index::newtype_index! {
#[orderable]
#[gate_rustc_only]
pub struct StackDepth {}
}
#[derive(derivative::Derivative)]
#[derivative(Debug(bound = ""))]
struct StackEntry<X: Cx> {
input: X::Input,
available_depth: AvailableDepth,
/// The maximum depth reached by this stack entry, only up-to date
/// for the top of the stack and lazily updated for the rest.
reached_depth: StackDepth,
/// Whether this entry is a non-root cycle participant.
///
/// We must not move the result of non-root cycle participants to the
/// global cache. We store the highest stack depth of a head of a cycle
/// this goal is involved in. This necessary to soundly cache its
/// provisional result.
non_root_cycle_participant: Option<StackDepth>,
encountered_overflow: bool,
has_been_used: Option<UsageKind>,
/// We put only the root goal of a coinductive cycle into the global cache.
///
/// If we were to use that result when later trying to prove another cycle
/// participant, we can end up with unstable query results.
///
/// See tests/ui/next-solver/coinduction/incompleteness-unstable-result.rs for
/// an example of where this is needed.
///
/// There can be multiple roots on the same stack, so we need to track
/// cycle participants per root:
/// ```plain
/// A :- B
/// B :- A, C
/// C :- D
/// D :- C
/// ```
nested_goals: HashSet<X::Input>,
/// Starts out as `None` and gets set when rerunning this
/// goal in case we encounter a cycle.
provisional_result: Option<X::Result>,
}
/// The provisional result for a goal which is not on the stack.
#[derive(Debug)]
struct DetachedEntry<X: Cx> {
/// The head of the smallest non-trivial cycle involving this entry.
///
/// Given the following rules, when proving `A` the head for
/// the provisional entry of `C` would be `B`.
/// ```plain
/// A :- B
/// B :- C
/// C :- A + B + C
/// ```
head: StackDepth,
result: X::Result,
}
/// Stores the stack depth of a currently evaluated goal *and* already
/// computed results for goals which depend on other goals still on the stack.
///
/// The provisional result may depend on whether the stack above it is inductive
/// or coinductive. Because of this, we store separate provisional results for
/// each case. If an provisional entry is not applicable, it may be the case
/// that we already have provisional result while computing a goal. In this case
/// we prefer the provisional result to potentially avoid fixpoint iterations.
/// See tests/ui/traits/next-solver/cycles/mixed-cycles-2.rs for an example.
///
/// The provisional cache can theoretically result in changes to the observable behavior,
/// see tests/ui/traits/next-solver/cycles/provisional-cache-impacts-behavior.rs.
#[derive(derivative::Derivative)]
#[derivative(Default(bound = ""))]
struct ProvisionalCacheEntry<X: Cx> {
stack_depth: Option<StackDepth>,
with_inductive_stack: Option<DetachedEntry<X>>,
with_coinductive_stack: Option<DetachedEntry<X>>,
}
impl<X: Cx> ProvisionalCacheEntry<X> {
fn is_empty(&self) -> bool {
self.stack_depth.is_none()
&& self.with_inductive_stack.is_none()
&& self.with_coinductive_stack.is_none()
}
}
pub struct SearchGraph<D: Delegate<Cx = X>, X: Cx = <D as Delegate>::Cx> {
mode: SolverMode,
/// The stack of goals currently being computed.
///
/// An element is *deeper* in the stack if its index is *lower*.
stack: IndexVec<StackDepth, StackEntry<X>>,
provisional_cache: HashMap<X::Input, ProvisionalCacheEntry<X>>,
_marker: PhantomData<D>,
}
impl<D: Delegate<Cx = X>, X: Cx> SearchGraph<D> {
pub fn new(mode: SolverMode) -> SearchGraph<D> {
Self {
mode,
stack: Default::default(),
provisional_cache: Default::default(),
_marker: PhantomData,
}
}
pub fn solver_mode(&self) -> SolverMode {
self.mode
}
fn update_parent_goal(&mut self, reached_depth: StackDepth, encountered_overflow: bool) {
if let Some(parent) = self.stack.raw.last_mut() {
parent.reached_depth = parent.reached_depth.max(reached_depth);
parent.encountered_overflow |= encountered_overflow;
}
}
pub fn is_empty(&self) -> bool {
self.stack.is_empty()
}
fn stack_coinductive_from(
cx: X,
stack: &IndexVec<StackDepth, StackEntry<X>>,
head: StackDepth,
) -> bool {
stack.raw[head.index()..].iter().all(|entry| D::step_is_coinductive(cx, entry.input))
}
// When encountering a solver cycle, the result of the current goal
// depends on goals lower on the stack.
//
// We have to therefore be careful when caching goals. Only the final result
// of the cycle root, i.e. the lowest goal on the stack involved in this cycle,
// is moved to the global cache while all others are stored in a provisional cache.
//
// We update both the head of this cycle to rerun its evaluation until
// we reach a fixpoint and all other cycle participants to make sure that
// their result does not get moved to the global cache.
fn tag_cycle_participants(
stack: &mut IndexVec<StackDepth, StackEntry<X>>,
usage_kind: Option<UsageKind>,
head: StackDepth,
) {
if let Some(usage_kind) = usage_kind {
stack[head].has_been_used =
Some(stack[head].has_been_used.map_or(usage_kind, |prev| prev.merge(usage_kind)));
}
debug_assert!(stack[head].has_been_used.is_some());
// The current root of these cycles. Note that this may not be the final
// root in case a later goal depends on a goal higher up the stack.
let mut current_root = head;
while let Some(parent) = stack[current_root].non_root_cycle_participant {
current_root = parent;
debug_assert!(stack[current_root].has_been_used.is_some());
}
let (stack, cycle_participants) = stack.raw.split_at_mut(head.index() + 1);
let current_cycle_root = &mut stack[current_root.as_usize()];
for entry in cycle_participants {
entry.non_root_cycle_participant = entry.non_root_cycle_participant.max(Some(head));
current_cycle_root.nested_goals.insert(entry.input);
current_cycle_root.nested_goals.extend(mem::take(&mut entry.nested_goals));
}
}
fn clear_dependent_provisional_results(
provisional_cache: &mut HashMap<X::Input, ProvisionalCacheEntry<X>>,
head: StackDepth,
) {
#[allow(rustc::potential_query_instability)]
provisional_cache.retain(|_, entry| {
if entry.with_coinductive_stack.as_ref().is_some_and(|p| p.head == head) {
entry.with_coinductive_stack.take();
}
if entry.with_inductive_stack.as_ref().is_some_and(|p| p.head == head) {
entry.with_inductive_stack.take();
}
!entry.is_empty()
});
}
/// Probably the most involved method of the whole solver.
///
/// Given some goal which is proven via the `prove_goal` closure, this
/// handles caching, overflow, and coinductive cycles.
pub fn with_new_goal(
&mut self,
cx: X,
input: X::Input,
inspect: &mut D::ProofTreeBuilder,
mut prove_goal: impl FnMut(&mut Self, &mut D::ProofTreeBuilder) -> X::Result,
) -> X::Result {
self.check_invariants();
// Check for overflow.
let Some(available_depth) = AvailableDepth::allowed_depth_for_nested::<D>(cx, &self.stack)
else {
if let Some(last) = self.stack.raw.last_mut() {
last.encountered_overflow = true;
}
debug!("encountered stack overflow");
return D::on_stack_overflow(cx, inspect, input);
};
if let Some(result) = self.lookup_global_cache(cx, input, available_depth, inspect) {
return result;
}
// Check whether the goal is in the provisional cache.
// The provisional result may rely on the path to its cycle roots,
// so we have to check the path of the current goal matches that of
// the cache entry.
let cache_entry = self.provisional_cache.entry(input).or_default();
if let Some(entry) = cache_entry
.with_coinductive_stack
.as_ref()
.filter(|p| Self::stack_coinductive_from(cx, &self.stack, p.head))
.or_else(|| {
cache_entry
.with_inductive_stack
.as_ref()
.filter(|p| !Self::stack_coinductive_from(cx, &self.stack, p.head))
})
{
debug!("provisional cache hit");
// We have a nested goal which is already in the provisional cache, use
// its result. We do not provide any usage kind as that should have been
// already set correctly while computing the cache entry.
inspect.on_provisional_cache_hit();
Self::tag_cycle_participants(&mut self.stack, None, entry.head);
return entry.result;
} else if let Some(stack_depth) = cache_entry.stack_depth {
debug!("encountered cycle with depth {stack_depth:?}");
// We have a nested goal which directly relies on a goal deeper in the stack.
//
// We start by tagging all cycle participants, as that's necessary for caching.
//
// Finally we can return either the provisional response or the initial response
// in case we're in the first fixpoint iteration for this goal.
inspect.on_cycle_in_stack();
let is_coinductive_cycle = Self::stack_coinductive_from(cx, &self.stack, stack_depth);
let cycle_kind =
if is_coinductive_cycle { CycleKind::Coinductive } else { CycleKind::Inductive };
Self::tag_cycle_participants(
&mut self.stack,
Some(UsageKind::Single(cycle_kind)),
stack_depth,
);
// Return the provisional result or, if we're in the first iteration,
// start with no constraints.
return if let Some(result) = self.stack[stack_depth].provisional_result {
result
} else {
D::initial_provisional_result(cx, cycle_kind, input)
};
} else {
// No entry, we push this goal on the stack and try to prove it.
let depth = self.stack.next_index();
let entry = StackEntry {
input,
available_depth,
reached_depth: depth,
non_root_cycle_participant: None,
encountered_overflow: false,
has_been_used: None,
nested_goals: Default::default(),
provisional_result: None,
};
assert_eq!(self.stack.push(entry), depth);
cache_entry.stack_depth = Some(depth);
};
// This is for global caching, so we properly track query dependencies.
// Everything that affects the `result` should be performed within this
// `with_anon_task` closure. If computing this goal depends on something
// not tracked by the cache key and from outside of this anon task, it
// must not be added to the global cache. Notably, this is the case for
// trait solver cycles participants.
let ((final_entry, result), dep_node) = cx.with_cached_task(|| {
for _ in 0..D::FIXPOINT_STEP_LIMIT {
match self.fixpoint_step_in_task(cx, input, inspect, &mut prove_goal) {
StepResult::Done(final_entry, result) => return (final_entry, result),
StepResult::HasChanged => debug!("fixpoint changed provisional results"),
}
}
debug!("canonical cycle overflow");
let current_entry = self.stack.pop().unwrap();
debug_assert!(current_entry.has_been_used.is_none());
let result = D::on_fixpoint_overflow(cx, input);
(current_entry, result)
});
let proof_tree = inspect.finalize_canonical_goal_evaluation(cx);
self.update_parent_goal(final_entry.reached_depth, final_entry.encountered_overflow);
// We're now done with this goal. In case this goal is involved in a larger cycle
// do not remove it from the provisional cache and update its provisional result.
// We only add the root of cycles to the global cache.
if let Some(head) = final_entry.non_root_cycle_participant {
let coinductive_stack = Self::stack_coinductive_from(cx, &self.stack, head);
let entry = self.provisional_cache.get_mut(&input).unwrap();
entry.stack_depth = None;
if coinductive_stack {
entry.with_coinductive_stack = Some(DetachedEntry { head, result });
} else {
entry.with_inductive_stack = Some(DetachedEntry { head, result });
}
} else {
// When encountering a cycle, both inductive and coinductive, we only
// move the root into the global cache. We also store all other cycle
// participants involved.
//
// We must not use the global cache entry of a root goal if a cycle
// participant is on the stack. This is necessary to prevent unstable
// results. See the comment of `StackEntry::nested_goals` for
// more details.
self.provisional_cache.remove(&input);
let additional_depth = final_entry.reached_depth.as_usize() - self.stack.len();
cx.with_global_cache(self.mode, |cache| {
cache.insert(
cx,
input,
result,
proof_tree,
dep_node,
additional_depth,
final_entry.encountered_overflow,
&final_entry.nested_goals,
)
})
}
self.check_invariants();
result
}
/// Try to fetch a previously computed result from the global cache,
/// making sure to only do so if it would match the result of reevaluating
/// this goal.
fn lookup_global_cache(
&mut self,
cx: X,
input: X::Input,
available_depth: AvailableDepth,
inspect: &mut D::ProofTreeBuilder,
) -> Option<X::Result> {
cx.with_global_cache(self.mode, |cache| {
let CacheData {
result,
proof_tree,
additional_depth,
encountered_overflow,
nested_goals: _, // FIXME: consider nested goals here.
} = cache.get(cx, input, &self.stack, available_depth)?;
// If we're building a proof tree and the current cache entry does not
// contain a proof tree, we do not use the entry but instead recompute
// the goal. We simply overwrite the existing entry once we're done,
// caching the proof tree.
if !inspect.try_apply_proof_tree(proof_tree) {
return None;
}
// Update the reached depth of the current goal to make sure
// its state is the same regardless of whether we've used the
// global cache or not.
let reached_depth = self.stack.next_index().plus(additional_depth);
self.update_parent_goal(reached_depth, encountered_overflow);
debug!("global cache hit");
Some(result)
})
}
}
enum StepResult<X: Cx> {
Done(StackEntry<X>, X::Result),
HasChanged,
}
impl<D: Delegate<Cx = X>, X: Cx> SearchGraph<D> {
/// When we encounter a coinductive cycle, we have to fetch the
/// result of that cycle while we are still computing it. Because
/// of this we continuously recompute the cycle until the result
/// of the previous iteration is equal to the final result, at which
/// point we are done.
fn fixpoint_step_in_task<F>(
&mut self,
cx: X,
input: X::Input,
inspect: &mut D::ProofTreeBuilder,
prove_goal: &mut F,
) -> StepResult<X>
where
F: FnMut(&mut Self, &mut D::ProofTreeBuilder) -> X::Result,
{
let result = prove_goal(self, inspect);
let stack_entry = self.stack.pop().unwrap();
debug_assert_eq!(stack_entry.input, input);
// If the current goal is not the root of a cycle, we are done.
let Some(usage_kind) = stack_entry.has_been_used else {
return StepResult::Done(stack_entry, result);
};
// If it is a cycle head, we have to keep trying to prove it until
// we reach a fixpoint. We need to do so for all cycle heads,
// not only for the root.
//
// See tests/ui/traits/next-solver/cycles/fixpoint-rerun-all-cycle-heads.rs
// for an example.
// Start by clearing all provisional cache entries which depend on this
// the current goal.
Self::clear_dependent_provisional_results(
&mut self.provisional_cache,
self.stack.next_index(),
);
// Check whether we reached a fixpoint, either because the final result
// is equal to the provisional result of the previous iteration, or because
// this was only the root of either coinductive or inductive cycles, and the
// final result is equal to the initial response for that case.
//
// If we did not reach a fixpoint, update the provisional result and reevaluate.
if D::reached_fixpoint(cx, usage_kind, input, stack_entry.provisional_result, result) {
StepResult::Done(stack_entry, result)
} else {
let depth = self.stack.push(StackEntry {
has_been_used: None,
provisional_result: Some(result),
..stack_entry
});
debug_assert_eq!(self.provisional_cache[&input].stack_depth, Some(depth));
StepResult::HasChanged
}
}
}

75
compiler/rustc_type_ir/src/search_graph/validate.rs Normal file
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@ -0,0 +1,75 @@
use super::*;
impl<D: Delegate<Cx = X>, X: Cx> SearchGraph<D> {
#[allow(rustc::potential_query_instability)]
pub(super) fn check_invariants(&self) {
if !cfg!(debug_assertions) {
return;
}
let SearchGraph { mode: _, stack, provisional_cache, _marker } = self;
if stack.is_empty() {
assert!(provisional_cache.is_empty());
}
for (depth, entry) in stack.iter_enumerated() {
let StackEntry {
input,
available_depth: _,
reached_depth: _,
non_root_cycle_participant,
encountered_overflow: _,
has_been_used,
ref nested_goals,
provisional_result,
} = *entry;
let cache_entry = provisional_cache.get(&entry.input).unwrap();
assert_eq!(cache_entry.stack_depth, Some(depth));
if let Some(head) = non_root_cycle_participant {
assert!(head < depth);
assert!(nested_goals.is_empty());
assert_ne!(stack[head].has_been_used, None);
let mut current_root = head;
while let Some(parent) = stack[current_root].non_root_cycle_participant {
current_root = parent;
}
assert!(stack[current_root].nested_goals.contains(&input));
}
if !nested_goals.is_empty() {
assert!(provisional_result.is_some() || has_been_used.is_some());
for entry in stack.iter().take(depth.as_usize()) {
assert_eq!(nested_goals.get(&entry.input), None);
}
}
}
for (&input, entry) in &self.provisional_cache {
let ProvisionalCacheEntry { stack_depth, with_coinductive_stack, with_inductive_stack } =
entry;
assert!(
stack_depth.is_some()
|| with_coinductive_stack.is_some()
|| with_inductive_stack.is_some()
);
if let &Some(stack_depth) = stack_depth {
assert_eq!(stack[stack_depth].input, input);
}
let check_detached = |detached_entry: &DetachedEntry<X>| {
let DetachedEntry { head, result: _ } = *detached_entry;
assert_ne!(stack[head].has_been_used, None);
};
if let Some(with_coinductive_stack) = with_coinductive_stack {
check_detached(with_coinductive_stack);
}
if let Some(with_inductive_stack) = with_inductive_stack {
check_detached(with_inductive_stack);
}
}
}
}