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Rollup merge of #130273 - lcnr:overflow-no-constraints, r=compiler-errors

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more eagerly discard constraints on overflow

We always discard the results of overflowing goals inside of the trait solver. We previously did so when instantiating the response in `evaluate_goal`. Canonicalizing results only to later discard them is also  inefficient 🤷

It's simpler and nicer to debug to eagerly discard constraints inside of the query itself.

r? ``@compiler-errors``
This commit is contained in:
Matthias Krüger 2024-09-12 19:03:43 +02:00 • committed by GitHub
commit cb1d80d1e5
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5 changed files with 27 additions and 35 deletions
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15
compiler/rustc_next_trait_solver/src/solve/eval_ctxt/canonical.rs
View file

@ -122,6 +122,21 @@ where
(certainty, NestedNormalizationGoals::empty())
};
if let Certainty::Maybe(cause @ MaybeCause::Overflow { .. }) = certainty {
// If we have overflow, it's probable that we're substituting a type
// into itself infinitely and any partial substitutions in the query
// response are probably not useful anyways, so just return an empty
// query response.
//
// This may prevent us from potentially useful inference, e.g.
// 2 candidates, one ambiguous and one overflow, which both
// have the same inference constraints.
//
// Changing this to retain some constraints in the future
// won't be a breaking change, so this is good enough for now.
return Ok(self.make_ambiguous_response_no_constraints(cause));
}
let external_constraints =
self.compute_external_query_constraints(certainty, normalization_nested_goals);
let (var_values, mut external_constraints) = (self.var_values, external_constraints)

33
compiler/rustc_next_trait_solver/src/solve/eval_ctxt/mod.rs
View file

@ -17,7 +17,7 @@ use crate::delegate::SolverDelegate;
use crate::solve::inspect::{self, ProofTreeBuilder};
use crate::solve::search_graph::SearchGraph;
use crate::solve::{
CanonicalInput, CanonicalResponse, Certainty, Goal, GoalEvaluationKind, GoalSource, MaybeCause,
CanonicalInput, CanonicalResponse, Certainty, Goal, GoalEvaluationKind, GoalSource,
NestedNormalizationGoals, NoSolution, PredefinedOpaquesData, QueryResult, SolverMode,
FIXPOINT_STEP_LIMIT,
};
@ -370,7 +370,7 @@ where
canonical_goal,
&mut goal_evaluation,
);
let canonical_response = match canonical_response {
let response = match canonical_response {
Err(e) => {
self.inspect.goal_evaluation(goal_evaluation);
return Err(e);
@ -378,12 +378,11 @@ where
Ok(response) => response,
};
let (normalization_nested_goals, certainty, has_changed) = self
.instantiate_response_discarding_overflow(
goal.param_env,
orig_values,
canonical_response,
);
let has_changed = !response.value.var_values.is_identity_modulo_regions()
|| !response.value.external_constraints.opaque_types.is_empty();
let (normalization_nested_goals, certainty) =
self.instantiate_and_apply_query_response(goal.param_env, orig_values, response);
self.inspect.goal_evaluation(goal_evaluation);
// FIXME: We previously had an assert here that checked that recomputing
// a goal after applying its constraints did not change its response.
@ -398,24 +397,6 @@ where
Ok((normalization_nested_goals, has_changed, certainty))
}
fn instantiate_response_discarding_overflow(
&mut self,
param_env: I::ParamEnv,
original_values: Vec<I::GenericArg>,
response: CanonicalResponse<I>,
) -> (NestedNormalizationGoals<I>, Certainty, bool) {
if let Certainty::Maybe(MaybeCause::Overflow { .. }) = response.value.certainty {
return (NestedNormalizationGoals::empty(), response.value.certainty, false);
}
let has_changed = !response.value.var_values.is_identity_modulo_regions()
|| !response.value.external_constraints.opaque_types.is_empty();
let (normalization_nested_goals, certainty) =
self.instantiate_and_apply_query_response(param_env, original_values, response);
(normalization_nested_goals, certainty, has_changed)
}
fn compute_goal(&mut self, goal: Goal<I, I::Predicate>) -> QueryResult<I> {
let Goal { param_env, predicate } = goal;
let kind = predicate.kind();