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Rollup merge of rust-lang#128828 - lcnr:search-graph-11, r=compiler-e…
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…rrors

`-Znext-solver` caching

This PR has two major changes while also fixing multiple issues found via fuzzing.

The main optimization is the ability to not discard provisional cache entries when popping the highest cycle head the entry depends on. This fixes the hang in Fuchsia with `-Znext-solver=coherence`.

It also bails if the result of a fixpoint iteration is ambiguous, even without reaching a fixpoint. This is necessary to avoid exponential blowup if a coinductive cycle results in ambiguity, e.g. due to unknowable candidates in coherence.

Updating stack entries pretty much exclusively happens lazily now, so `fn check_invariants` ended up being mostly useless and I've removed it. See https://gist.github.com/lcnr/8de338fdb2685581e17727bbfab0622a for the invariants we would be able to assert with it.

For a general overview, see the in-process update of the relevant rustc-dev-guide chapter: https://hackmd.io/1ALkSjKlSCyQG-dVb_PUHw

r? ``@compiler-errors``
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matthiaskrgr authored Aug 14, 2024
2 parents 9859bf2 + 0aa17a4 commit 241f1d5
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Showing 13 changed files with 892 additions and 631 deletions.
4 changes: 0 additions & 4 deletions compiler/rustc_middle/src/arena.rs
Original file line number Diff line number Diff line change
Expand Up @@ -61,10 +61,6 @@ macro_rules! arena_types {
[] dtorck_constraint: rustc_middle::traits::query::DropckConstraint<'tcx>,
[] candidate_step: rustc_middle::traits::query::CandidateStep<'tcx>,
[] autoderef_bad_ty: rustc_middle::traits::query::MethodAutoderefBadTy<'tcx>,
[] canonical_goal_evaluation:
rustc_type_ir::solve::inspect::CanonicalGoalEvaluationStep<
rustc_middle::ty::TyCtxt<'tcx>
>,
[] query_region_constraints: rustc_middle::infer::canonical::QueryRegionConstraints<'tcx>,
[] type_op_subtype:
rustc_middle::infer::canonical::Canonical<'tcx,
Expand Down
9 changes: 0 additions & 9 deletions compiler/rustc_middle/src/ty/context.rs
Original file line number Diff line number Diff line change
Expand Up @@ -107,8 +107,6 @@ impl<'tcx> Interner for TyCtxt<'tcx> {
self.mk_predefined_opaques_in_body(data)
}
type DefiningOpaqueTypes = &'tcx ty::List<LocalDefId>;
type CanonicalGoalEvaluationStepRef =
&'tcx solve::inspect::CanonicalGoalEvaluationStep<TyCtxt<'tcx>>;
type CanonicalVars = CanonicalVarInfos<'tcx>;
fn mk_canonical_var_infos(self, infos: &[ty::CanonicalVarInfo<Self>]) -> Self::CanonicalVars {
self.mk_canonical_var_infos(infos)
Expand Down Expand Up @@ -277,13 +275,6 @@ impl<'tcx> Interner for TyCtxt<'tcx> {
self.debug_assert_args_compatible(def_id, args);
}

fn intern_canonical_goal_evaluation_step(
self,
step: solve::inspect::CanonicalGoalEvaluationStep<TyCtxt<'tcx>>,
) -> &'tcx solve::inspect::CanonicalGoalEvaluationStep<TyCtxt<'tcx>> {
self.arena.alloc(step)
}

fn mk_type_list_from_iter<I, T>(self, args: I) -> T::Output
where
I: Iterator<Item = T>,
Expand Down
106 changes: 14 additions & 92 deletions compiler/rustc_next_trait_solver/src/solve/inspect/build.rs
Original file line number Diff line number Diff line change
Expand Up @@ -5,11 +5,10 @@
//! see the comment on [ProofTreeBuilder].
use std::marker::PhantomData;
use std::mem;

use derive_where::derive_where;
use rustc_type_ir::inherent::*;
use rustc_type_ir::{self as ty, search_graph, Interner};
use rustc_type_ir::{self as ty, Interner};

use crate::delegate::SolverDelegate;
use crate::solve::eval_ctxt::canonical;
Expand Down Expand Up @@ -94,31 +93,10 @@ impl<I: Interner> WipGoalEvaluation<I> {
}
}

#[derive_where(PartialEq, Eq; I: Interner)]
pub(in crate::solve) enum WipCanonicalGoalEvaluationKind<I: Interner> {
Overflow,
CycleInStack,
ProvisionalCacheHit,
Interned { final_revision: I::CanonicalGoalEvaluationStepRef },
}

impl<I: Interner> std::fmt::Debug for WipCanonicalGoalEvaluationKind<I> {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
match self {
Self::Overflow => write!(f, "Overflow"),
Self::CycleInStack => write!(f, "CycleInStack"),
Self::ProvisionalCacheHit => write!(f, "ProvisionalCacheHit"),
Self::Interned { final_revision: _ } => {
f.debug_struct("Interned").finish_non_exhaustive()
}
}
}
}

#[derive_where(PartialEq, Eq, Debug; I: Interner)]
struct WipCanonicalGoalEvaluation<I: Interner> {
goal: CanonicalInput<I>,
kind: Option<WipCanonicalGoalEvaluationKind<I>>,
encountered_overflow: bool,
/// Only used for uncached goals. After we finished evaluating
/// the goal, this is interned and moved into `kind`.
final_revision: Option<WipCanonicalGoalEvaluationStep<I>>,
Expand All @@ -127,25 +105,17 @@ struct WipCanonicalGoalEvaluation<I: Interner> {

impl<I: Interner> WipCanonicalGoalEvaluation<I> {
fn finalize(self) -> inspect::CanonicalGoalEvaluation<I> {
// We've already interned the final revision in
// `fn finalize_canonical_goal_evaluation`.
assert!(self.final_revision.is_none());
let kind = match self.kind.unwrap() {
WipCanonicalGoalEvaluationKind::Overflow => {
inspect::CanonicalGoalEvaluation {
goal: self.goal,
kind: if self.encountered_overflow {
assert!(self.final_revision.is_none());
inspect::CanonicalGoalEvaluationKind::Overflow
}
WipCanonicalGoalEvaluationKind::CycleInStack => {
inspect::CanonicalGoalEvaluationKind::CycleInStack
}
WipCanonicalGoalEvaluationKind::ProvisionalCacheHit => {
inspect::CanonicalGoalEvaluationKind::ProvisionalCacheHit
}
WipCanonicalGoalEvaluationKind::Interned { final_revision } => {
} else {
let final_revision = self.final_revision.unwrap().finalize();
inspect::CanonicalGoalEvaluationKind::Evaluation { final_revision }
}
};

inspect::CanonicalGoalEvaluation { goal: self.goal, kind, result: self.result.unwrap() }
},
result: self.result.unwrap(),
}
}
}

Expand Down Expand Up @@ -308,7 +278,7 @@ impl<D: SolverDelegate<Interner = I>, I: Interner> ProofTreeBuilder<D> {
) -> ProofTreeBuilder<D> {
self.nested(|| WipCanonicalGoalEvaluation {
goal,
kind: None,
encountered_overflow: false,
final_revision: None,
result: None,
})
Expand All @@ -329,11 +299,11 @@ impl<D: SolverDelegate<Interner = I>, I: Interner> ProofTreeBuilder<D> {
}
}

pub fn canonical_goal_evaluation_kind(&mut self, kind: WipCanonicalGoalEvaluationKind<I>) {
pub fn canonical_goal_evaluation_overflow(&mut self) {
if let Some(this) = self.as_mut() {
match this {
DebugSolver::CanonicalGoalEvaluation(canonical_goal_evaluation) => {
assert_eq!(canonical_goal_evaluation.kind.replace(kind), None);
canonical_goal_evaluation.encountered_overflow = true;
}
_ => unreachable!(),
};
Expand Down Expand Up @@ -547,51 +517,3 @@ 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!(),
})
}
}
66 changes: 44 additions & 22 deletions compiler/rustc_next_trait_solver/src/solve/search_graph.rs
Original file line number Diff line number Diff line change
@@ -1,12 +1,13 @@
use std::convert::Infallible;
use std::marker::PhantomData;

use rustc_type_ir::inherent::*;
use rustc_type_ir::search_graph::{self, CycleKind, UsageKind};
use rustc_type_ir::search_graph::{self, PathKind};
use rustc_type_ir::solve::{CanonicalInput, Certainty, QueryResult};
use rustc_type_ir::Interner;

use super::inspect::{self, ProofTreeBuilder};
use super::FIXPOINT_STEP_LIMIT;
use super::inspect::ProofTreeBuilder;
use super::{has_no_inference_or_external_constraints, FIXPOINT_STEP_LIMIT};
use crate::delegate::SolverDelegate;

/// This type is never constructed. We only use it to implement `search_graph::Delegate`
Expand All @@ -22,43 +23,48 @@ where
{
type Cx = D::Interner;

const ENABLE_PROVISIONAL_CACHE: bool = true;
type ValidationScope = Infallible;
fn enter_validation_scope(
_cx: Self::Cx,
_input: CanonicalInput<I>,
) -> Option<Self::ValidationScope> {
None
}

const FIXPOINT_STEP_LIMIT: usize = FIXPOINT_STEP_LIMIT;

type ProofTreeBuilder = ProofTreeBuilder<D>;
fn inspect_is_noop(inspect: &mut Self::ProofTreeBuilder) -> bool {
inspect.is_noop()
}

const DIVIDE_AVAILABLE_DEPTH_ON_OVERFLOW: usize = 4;
fn recursion_limit(cx: I) -> usize {
cx.recursion_limit()
}

fn initial_provisional_result(
cx: I,
kind: CycleKind,
kind: PathKind,
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)),
PathKind::Coinductive => response_no_constraints(cx, input, Certainty::Yes),
PathKind::Inductive => response_no_constraints(cx, input, Certainty::overflow(false)),
}
}

fn reached_fixpoint(
cx: I,
kind: UsageKind,
fn is_initial_provisional_result(
cx: Self::Cx,
kind: PathKind,
input: CanonicalInput<I>,
provisional_result: Option<QueryResult<I>>,
result: QueryResult<I>,
) -> bool {
if let Some(r) = provisional_result {
r == result
} else {
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,
match kind {
PathKind::Coinductive => response_no_constraints(cx, input, Certainty::Yes) == result,
PathKind::Inductive => {
response_no_constraints(cx, input, Certainty::overflow(false)) == result
}
}
}
Expand All @@ -68,14 +74,30 @@ where
inspect: &mut ProofTreeBuilder<D>,
input: CanonicalInput<I>,
) -> QueryResult<I> {
inspect.canonical_goal_evaluation_kind(inspect::WipCanonicalGoalEvaluationKind::Overflow);
inspect.canonical_goal_evaluation_overflow();
response_no_constraints(cx, input, Certainty::overflow(true))
}

fn on_fixpoint_overflow(cx: I, input: CanonicalInput<I>) -> QueryResult<I> {
response_no_constraints(cx, input, Certainty::overflow(false))
}

fn is_ambiguous_result(result: QueryResult<I>) -> bool {
result.is_ok_and(|response| {
has_no_inference_or_external_constraints(response)
&& matches!(response.value.certainty, Certainty::Maybe(_))
})
}

fn propagate_ambiguity(
cx: I,
for_input: CanonicalInput<I>,
from_result: QueryResult<I>,
) -> QueryResult<I> {
let certainty = from_result.unwrap().value.certainty;
response_no_constraints(cx, for_input, certainty)
}

fn step_is_coinductive(cx: I, input: CanonicalInput<I>) -> bool {
input.value.goal.predicate.is_coinductive(cx)
}
Expand Down
10 changes: 3 additions & 7 deletions compiler/rustc_trait_selection/src/solve/inspect/analyse.rs
Original file line number Diff line number Diff line change
Expand Up @@ -334,13 +334,9 @@ impl<'a, 'tcx> InspectGoal<'a, 'tcx> {

pub fn candidates(&'a self) -> Vec<InspectCandidate<'a, 'tcx>> {
let mut candidates = vec![];
let last_eval_step = match self.evaluation_kind {
inspect::CanonicalGoalEvaluationKind::Overflow
| inspect::CanonicalGoalEvaluationKind::CycleInStack
| inspect::CanonicalGoalEvaluationKind::ProvisionalCacheHit => {
warn!("unexpected root evaluation: {:?}", self.evaluation_kind);
return vec![];
}
let last_eval_step = match &self.evaluation_kind {
// An annoying edge case in case the recursion limit is 0.
inspect::CanonicalGoalEvaluationKind::Overflow => return vec![],
inspect::CanonicalGoalEvaluationKind::Evaluation { final_revision } => final_revision,
};

Expand Down
24 changes: 8 additions & 16 deletions compiler/rustc_type_ir/src/binder.rs
Original file line number Diff line number Diff line change
Expand Up @@ -8,7 +8,7 @@ use derive_where::derive_where;
use rustc_macros::{HashStable_NoContext, TyDecodable, TyEncodable};
#[cfg(feature = "nightly")]
use rustc_serialize::Decodable;
use tracing::debug;
use tracing::instrument;

use crate::data_structures::SsoHashSet;
use crate::fold::{FallibleTypeFolder, TypeFoldable, TypeFolder, TypeSuperFoldable};
Expand Down Expand Up @@ -817,28 +817,20 @@ impl<'a, I: Interner> ArgFolder<'a, I> {
/// As indicated in the diagram, here the same type `&'a i32` is instantiated once, but in the
/// first case we do not increase the De Bruijn index and in the second case we do. The reason
/// is that only in the second case have we passed through a fn binder.
#[instrument(level = "trace", skip(self), fields(binders_passed = self.binders_passed), ret)]
fn shift_vars_through_binders<T: TypeFoldable<I>>(&self, val: T) -> T {
debug!(
"shift_vars(val={:?}, binders_passed={:?}, has_escaping_bound_vars={:?})",
val,
self.binders_passed,
val.has_escaping_bound_vars()
);

if self.binders_passed == 0 || !val.has_escaping_bound_vars() {
return val;
val
} else {
ty::fold::shift_vars(self.cx, val, self.binders_passed)
}

let result = ty::fold::shift_vars(TypeFolder::cx(self), val, self.binders_passed);
debug!("shift_vars: shifted result = {:?}", result);

result
}

fn shift_region_through_binders(&self, region: I::Region) -> I::Region {
if self.binders_passed == 0 || !region.has_escaping_bound_vars() {
return region;
region
} else {
ty::fold::shift_region(self.cx, region, self.binders_passed)
}
ty::fold::shift_region(self.cx, region, self.binders_passed)
}
}
11 changes: 5 additions & 6 deletions compiler/rustc_type_ir/src/fold.rs
Original file line number Diff line number Diff line change
Expand Up @@ -48,7 +48,7 @@
use std::mem;

use rustc_index::{Idx, IndexVec};
use tracing::debug;
use tracing::instrument;

use crate::data_structures::Lrc;
use crate::inherent::*;
Expand Down Expand Up @@ -417,15 +417,14 @@ pub fn shift_region<I: Interner>(cx: I, region: I::Region, amount: u32) -> I::Re
}
}

#[instrument(level = "trace", skip(cx), ret)]
pub fn shift_vars<I: Interner, T>(cx: I, value: T, amount: u32) -> T
where
T: TypeFoldable<I>,
{
debug!("shift_vars(value={:?}, amount={})", value, amount);

if amount == 0 || !value.has_escaping_bound_vars() {
return value;
value
} else {
value.fold_with(&mut Shifter::new(cx, amount))
}

value.fold_with(&mut Shifter::new(cx, amount))
}
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