From d6fd45c2e3ee24bedbc1b7643b622ab97f29537f Mon Sep 17 00:00:00 2001 From: lcnr Date: Thu, 10 Oct 2024 09:26:49 +0000 Subject: [PATCH] impossible obligations check fast path --- .../src/solve/eval_ctxt/mod.rs | 72 ++++++++++++++----- .../rustc_next_trait_solver/src/solve/mod.rs | 8 +++ .../src/solve/search_graph.rs | 3 - compiler/rustc_trait_selection/src/solve.rs | 1 + .../src/solve/fulfill.rs | 15 ++-- .../src/traits/coherence.rs | 13 +++- .../rustc_type_ir/src/search_graph/mod.rs | 12 ++-- tests/crashes/124894.rs | 11 --- 8 files changed, 90 insertions(+), 45 deletions(-) delete mode 100644 tests/crashes/124894.rs diff --git a/compiler/rustc_next_trait_solver/src/solve/eval_ctxt/mod.rs b/compiler/rustc_next_trait_solver/src/solve/eval_ctxt/mod.rs index ffa800348f2..bc324dcbf51 100644 --- a/compiler/rustc_next_trait_solver/src/solve/eval_ctxt/mod.rs +++ b/compiler/rustc_next_trait_solver/src/solve/eval_ctxt/mod.rs @@ -18,8 +18,8 @@ use crate::solve::inspect::{self, ProofTreeBuilder}; use crate::solve::search_graph::SearchGraph; use crate::solve::{ CanonicalInput, CanonicalResponse, Certainty, FIXPOINT_STEP_LIMIT, Goal, GoalEvaluationKind, - GoalSource, NestedNormalizationGoals, NoSolution, PredefinedOpaquesData, QueryResult, - SolverMode, + GoalSource, HasChanged, NestedNormalizationGoals, NoSolution, PredefinedOpaquesData, + QueryResult, SolverMode, }; pub(super) mod canonical; @@ -126,11 +126,31 @@ pub enum GenerateProofTree { } pub trait SolverDelegateEvalExt: SolverDelegate { + /// Evaluates a goal from **outside** of the trait solver. + /// + /// Using this while inside of the solver is wrong as it uses a new + /// search graph which would break cycle detection. fn evaluate_root_goal( &self, goal: Goal::Predicate>, generate_proof_tree: GenerateProofTree, - ) -> (Result<(bool, Certainty), NoSolution>, Option>); + ) -> ( + Result<(HasChanged, Certainty), NoSolution>, + Option>, + ); + + /// Check whether evaluating `goal` with a depth of `root_depth` may + /// succeed. This only returns `false` if the goal is guaranteed to + /// not hold. In case evaluation overflows and fails with ambiguity this + /// returns `true`. + /// + /// This is only intended to be used as a performance optimization + /// in coherence checking. + fn root_goal_may_hold_with_depth( + &self, + root_depth: usize, + goal: Goal::Predicate>, + ) -> bool; // FIXME: This is only exposed because we need to use it in `analyse.rs` // which is not yet uplifted. Once that's done, we should remove this. @@ -139,7 +159,7 @@ pub trait SolverDelegateEvalExt: SolverDelegate { goal: Goal::Predicate>, generate_proof_tree: GenerateProofTree, ) -> ( - Result<(NestedNormalizationGoals, bool, Certainty), NoSolution>, + Result<(NestedNormalizationGoals, HasChanged, Certainty), NoSolution>, Option>, ); } @@ -149,31 +169,41 @@ where D: SolverDelegate, I: Interner, { - /// Evaluates a goal from **outside** of the trait solver. - /// - /// Using this while inside of the solver is wrong as it uses a new - /// search graph which would break cycle detection. #[instrument(level = "debug", skip(self))] fn evaluate_root_goal( &self, goal: Goal, generate_proof_tree: GenerateProofTree, - ) -> (Result<(bool, Certainty), NoSolution>, Option>) { - EvalCtxt::enter_root(self, generate_proof_tree, |ecx| { + ) -> (Result<(HasChanged, Certainty), NoSolution>, Option>) { + EvalCtxt::enter_root(self, self.cx().recursion_limit(), generate_proof_tree, |ecx| { ecx.evaluate_goal(GoalEvaluationKind::Root, GoalSource::Misc, goal) }) } + fn root_goal_may_hold_with_depth( + &self, + root_depth: usize, + goal: Goal::Predicate>, + ) -> bool { + self.probe(|| { + EvalCtxt::enter_root(self, root_depth, GenerateProofTree::No, |ecx| { + ecx.evaluate_goal(GoalEvaluationKind::Root, GoalSource::Misc, goal) + }) + .0 + }) + .is_ok() + } + #[instrument(level = "debug", skip(self))] fn evaluate_root_goal_raw( &self, goal: Goal, generate_proof_tree: GenerateProofTree, ) -> ( - Result<(NestedNormalizationGoals, bool, Certainty), NoSolution>, + Result<(NestedNormalizationGoals, HasChanged, Certainty), NoSolution>, Option>, ) { - EvalCtxt::enter_root(self, generate_proof_tree, |ecx| { + EvalCtxt::enter_root(self, self.cx().recursion_limit(), generate_proof_tree, |ecx| { ecx.evaluate_goal_raw(GoalEvaluationKind::Root, GoalSource::Misc, goal) }) } @@ -197,10 +227,11 @@ where /// over using this manually (such as [`SolverDelegateEvalExt::evaluate_root_goal`]). pub(super) fn enter_root( delegate: &D, + root_depth: usize, generate_proof_tree: GenerateProofTree, f: impl FnOnce(&mut EvalCtxt<'_, D>) -> R, ) -> (R, Option>) { - let mut search_graph = SearchGraph::new(delegate.solver_mode()); + let mut search_graph = SearchGraph::new(delegate.solver_mode(), root_depth); let mut ecx = EvalCtxt { delegate, @@ -339,7 +370,7 @@ where goal_evaluation_kind: GoalEvaluationKind, source: GoalSource, goal: Goal, - ) -> Result<(bool, Certainty), NoSolution> { + ) -> Result<(HasChanged, Certainty), NoSolution> { let (normalization_nested_goals, has_changed, certainty) = self.evaluate_goal_raw(goal_evaluation_kind, source, goal)?; assert!(normalization_nested_goals.is_empty()); @@ -360,7 +391,7 @@ where goal_evaluation_kind: GoalEvaluationKind, _source: GoalSource, goal: Goal, - ) -> Result<(NestedNormalizationGoals, bool, Certainty), NoSolution> { + ) -> Result<(NestedNormalizationGoals, HasChanged, Certainty), NoSolution> { let (orig_values, canonical_goal) = self.canonicalize_goal(goal); let mut goal_evaluation = self.inspect.new_goal_evaluation(goal, &orig_values, goal_evaluation_kind); @@ -378,8 +409,13 @@ where Ok(response) => response, }; - let has_changed = !response.value.var_values.is_identity_modulo_regions() - || !response.value.external_constraints.opaque_types.is_empty(); + let has_changed = if !response.value.var_values.is_identity_modulo_regions() + || !response.value.external_constraints.opaque_types.is_empty() + { + HasChanged::Yes + } else { + HasChanged::No + }; let (normalization_nested_goals, certainty) = self.instantiate_and_apply_query_response(goal.param_env, orig_values, response); @@ -552,7 +588,7 @@ where for (source, goal) in goals.goals { let (has_changed, certainty) = self.evaluate_goal(GoalEvaluationKind::Nested, source, goal)?; - if has_changed { + if has_changed == HasChanged::Yes { unchanged_certainty = None; } diff --git a/compiler/rustc_next_trait_solver/src/solve/mod.rs b/compiler/rustc_next_trait_solver/src/solve/mod.rs index 309ab7f28d1..97f7c71f3fc 100644 --- a/compiler/rustc_next_trait_solver/src/solve/mod.rs +++ b/compiler/rustc_next_trait_solver/src/solve/mod.rs @@ -48,6 +48,14 @@ enum GoalEvaluationKind { Nested, } +/// Whether evaluating this goal ended up changing the +/// inference state. +#[derive(PartialEq, Eq, Debug, Hash, Clone, Copy)] +pub enum HasChanged { + Yes, + No, +} + // FIXME(trait-system-refactor-initiative#117): we don't detect whether a response // ended up pulling down any universes. fn has_no_inference_or_external_constraints( diff --git a/compiler/rustc_next_trait_solver/src/solve/search_graph.rs b/compiler/rustc_next_trait_solver/src/solve/search_graph.rs index e47cc03f5ad..0e3f179b0c8 100644 --- a/compiler/rustc_next_trait_solver/src/solve/search_graph.rs +++ b/compiler/rustc_next_trait_solver/src/solve/search_graph.rs @@ -40,9 +40,6 @@ where } const DIVIDE_AVAILABLE_DEPTH_ON_OVERFLOW: usize = 4; - fn recursion_limit(cx: I) -> usize { - cx.recursion_limit() - } fn initial_provisional_result( cx: I, diff --git a/compiler/rustc_trait_selection/src/solve.rs b/compiler/rustc_trait_selection/src/solve.rs index e47f5389cd1..d425ab50ae0 100644 --- a/compiler/rustc_trait_selection/src/solve.rs +++ b/compiler/rustc_trait_selection/src/solve.rs @@ -6,6 +6,7 @@ pub mod inspect; mod normalize; mod select; +pub(crate) use delegate::SolverDelegate; pub use fulfill::{FulfillmentCtxt, NextSolverError}; pub(crate) use normalize::deeply_normalize_for_diagnostics; pub use normalize::{deeply_normalize, deeply_normalize_with_skipped_universes}; diff --git a/compiler/rustc_trait_selection/src/solve/fulfill.rs b/compiler/rustc_trait_selection/src/solve/fulfill.rs index c6e3ba3c957..081d7a6a769 100644 --- a/compiler/rustc_trait_selection/src/solve/fulfill.rs +++ b/compiler/rustc_trait_selection/src/solve/fulfill.rs @@ -12,7 +12,7 @@ use rustc_infer::traits::{ use rustc_middle::bug; use rustc_middle::ty::error::{ExpectedFound, TypeError}; use rustc_middle::ty::{self, TyCtxt}; -use rustc_next_trait_solver::solve::{GenerateProofTree, SolverDelegateEvalExt as _}; +use rustc_next_trait_solver::solve::{GenerateProofTree, HasChanged, SolverDelegateEvalExt as _}; use tracing::instrument; use super::Certainty; @@ -86,10 +86,7 @@ impl<'tcx> ObligationStorage<'tcx> { let result = <&SolverDelegate<'tcx>>::from(infcx) .evaluate_root_goal(goal, GenerateProofTree::No) .0; - match result { - Ok((has_changed, _)) => has_changed, - _ => false, - } + matches!(result, Ok((HasChanged::Yes, _))) })); }) } @@ -113,7 +110,7 @@ impl<'tcx, E: 'tcx> FulfillmentCtxt<'tcx, E> { &self, infcx: &InferCtxt<'tcx>, obligation: &PredicateObligation<'tcx>, - result: &Result<(bool, Certainty), NoSolution>, + result: &Result<(HasChanged, Certainty), NoSolution>, ) { if let Some(inspector) = infcx.obligation_inspector.get() { let result = match result { @@ -181,7 +178,11 @@ where continue; } }; - has_changed |= changed; + + if changed == HasChanged::Yes { + has_changed = true; + } + match certainty { Certainty::Yes => {} Certainty::Maybe(_) => self.obligations.register(obligation), diff --git a/compiler/rustc_trait_selection/src/traits/coherence.rs b/compiler/rustc_trait_selection/src/traits/coherence.rs index 27d2a3c15b9..b29e41beab5 100644 --- a/compiler/rustc_trait_selection/src/traits/coherence.rs +++ b/compiler/rustc_trait_selection/src/traits/coherence.rs @@ -19,6 +19,7 @@ use rustc_middle::ty::fast_reject::DeepRejectCtxt; use rustc_middle::ty::visit::{TypeSuperVisitable, TypeVisitable, TypeVisitableExt, TypeVisitor}; use rustc_middle::ty::{self, Ty, TyCtxt}; pub use rustc_next_trait_solver::coherence::*; +use rustc_next_trait_solver::solve::SolverDelegateEvalExt; use rustc_span::symbol::sym; use rustc_span::{DUMMY_SP, Span}; use tracing::{debug, instrument, warn}; @@ -28,7 +29,7 @@ use crate::error_reporting::traits::suggest_new_overflow_limit; use crate::infer::InferOk; use crate::infer::outlives::env::OutlivesEnvironment; use crate::solve::inspect::{InspectGoal, ProofTreeInferCtxtExt, ProofTreeVisitor}; -use crate::solve::{deeply_normalize_for_diagnostics, inspect}; +use crate::solve::{SolverDelegate, deeply_normalize_for_diagnostics, inspect}; use crate::traits::query::evaluate_obligation::InferCtxtExt; use crate::traits::select::IntercrateAmbiguityCause; use crate::traits::{ @@ -333,6 +334,16 @@ fn impl_intersection_has_impossible_obligation<'a, 'cx, 'tcx>( let infcx = selcx.infcx; if infcx.next_trait_solver() { + // A fast path optimization, try evaluating all goals with + // a very low recursion depth and bail if any of them don't + // hold. + if !obligations.iter().all(|o| { + <&SolverDelegate<'tcx>>::from(infcx) + .root_goal_may_hold_with_depth(8, Goal::new(infcx.tcx, o.param_env, o.predicate)) + }) { + return IntersectionHasImpossibleObligations::Yes; + } + let ocx = ObligationCtxt::new_with_diagnostics(infcx); ocx.register_obligations(obligations.iter().cloned()); let errors_and_ambiguities = ocx.select_all_or_error(); diff --git a/compiler/rustc_type_ir/src/search_graph/mod.rs b/compiler/rustc_type_ir/src/search_graph/mod.rs index ac4d0795a92..f4fb03562de 100644 --- a/compiler/rustc_type_ir/src/search_graph/mod.rs +++ b/compiler/rustc_type_ir/src/search_graph/mod.rs @@ -81,7 +81,6 @@ pub trait Delegate { fn inspect_is_noop(inspect: &mut Self::ProofTreeBuilder) -> bool; const DIVIDE_AVAILABLE_DEPTH_ON_OVERFLOW: usize; - fn recursion_limit(cx: Self::Cx) -> usize; fn initial_provisional_result( cx: Self::Cx, @@ -156,7 +155,7 @@ impl AvailableDepth { /// the remaining depth of all nested goals to prevent hangs /// in case there is exponential blowup. fn allowed_depth_for_nested( - cx: D::Cx, + root_depth: AvailableDepth, stack: &IndexVec>, ) -> Option { if let Some(last) = stack.raw.last() { @@ -170,7 +169,7 @@ impl AvailableDepth { AvailableDepth(last.available_depth.0 - 1) }) } else { - Some(AvailableDepth(D::recursion_limit(cx))) + Some(root_depth) } } @@ -360,6 +359,7 @@ struct ProvisionalCacheEntry { pub struct SearchGraph, X: Cx = ::Cx> { mode: SolverMode, + root_depth: AvailableDepth, /// The stack of goals currently being computed. /// /// An element is *deeper* in the stack if its index is *lower*. @@ -374,9 +374,10 @@ pub struct SearchGraph, X: Cx = ::Cx> { } impl, X: Cx> SearchGraph { - pub fn new(mode: SolverMode) -> SearchGraph { + pub fn new(mode: SolverMode, root_depth: usize) -> SearchGraph { Self { mode, + root_depth: AvailableDepth(root_depth), stack: Default::default(), provisional_cache: Default::default(), _marker: PhantomData, @@ -460,7 +461,8 @@ impl, X: Cx> SearchGraph { inspect: &mut D::ProofTreeBuilder, mut evaluate_goal: impl FnMut(&mut Self, &mut D::ProofTreeBuilder) -> X::Result, ) -> X::Result { - let Some(available_depth) = AvailableDepth::allowed_depth_for_nested::(cx, &self.stack) + let Some(available_depth) = + AvailableDepth::allowed_depth_for_nested::(self.root_depth, &self.stack) else { return self.handle_overflow(cx, input, inspect); }; diff --git a/tests/crashes/124894.rs b/tests/crashes/124894.rs deleted file mode 100644 index 230cf4a89c1..00000000000 --- a/tests/crashes/124894.rs +++ /dev/null @@ -1,11 +0,0 @@ -//@ known-bug: rust-lang/rust#124894 -//@ compile-flags: -Znext-solver=coherence - -#![feature(generic_const_exprs)] - -pub trait IsTrue {} -impl IsZST for T where (): IsTrue<{ std::mem::size_of::() == 0 }> {} - -pub trait IsZST {} - -impl IsZST for IsZST {}