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Rollup merge of #114287 - lcnr:overflow, r=compiler-errors
update overflow handling in the new trait solver implements https://hackmd.io/QY0dfEOgSNWwU4oiGnVRLw?view. I want to clean up this doc and add it to the rustc-dev-guide, but I think this PR is ready for merge as is, even without the dev-guide entry. r? `@compiler-errors`
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,100 @@ | ||
| use super::{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; | ||
| /// The trait solver cache used by `-Ztrait-solver=next`. | ||
| /// | ||
| /// FIXME(@lcnr): link to some official documentation of how | ||
| /// this works. | ||
| #[derive(Default)] | ||
| pub struct EvaluationCache<'tcx> { | ||
| map: Lock<FxHashMap<CanonicalInput<'tcx>, CacheEntry<'tcx>>>, | ||
| } | ||
|
|
||
| pub struct CacheData<'tcx> { | ||
| pub result: QueryResult<'tcx>, | ||
| pub reached_depth: usize, | ||
| pub encountered_overflow: bool, | ||
| } | ||
|
|
||
| impl<'tcx> EvaluationCache<'tcx> { | ||
| /// Insert a final result into the global cache. | ||
| pub fn insert( | ||
| &self, | ||
| key: CanonicalInput<'tcx>, | ||
| reached_depth: usize, | ||
| did_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, result); | ||
| entry.cycle_participants.extend(cycle_participants); | ||
| if did_overflow { | ||
| entry.with_overflow.insert(reached_depth, data); | ||
| } else { | ||
| entry.success = Some(Success { data, reached_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 fn get( | ||
| &self, | ||
| tcx: TyCtxt<'tcx>, | ||
| key: CanonicalInput<'tcx>, | ||
| cycle_participant_in_stack: impl FnOnce(&FxHashSet<CanonicalInput<'tcx>>) -> bool, | ||
| available_depth: Limit, | ||
| ) -> Option<CacheData<'tcx>> { | ||
| let map = self.map.borrow(); | ||
| let entry = map.get(&key)?; | ||
|
|
||
| if cycle_participant_in_stack(&entry.cycle_participants) { | ||
| return None; | ||
| } | ||
|
|
||
| if let Some(ref success) = entry.success { | ||
| if available_depth.value_within_limit(success.reached_depth) { | ||
| return Some(CacheData { | ||
| result: success.data.get(tcx), | ||
| reached_depth: success.reached_depth, | ||
| encountered_overflow: false, | ||
| }); | ||
| } | ||
| } | ||
|
|
||
| entry.with_overflow.get(&available_depth.0).map(|e| CacheData { | ||
| result: e.get(tcx), | ||
| reached_depth: available_depth.0, | ||
| encountered_overflow: true, | ||
| }) | ||
| } | ||
| } | ||
|
|
||
| struct Success<'tcx> { | ||
| data: WithDepNode<QueryResult<'tcx>>, | ||
| reached_depth: usize, | ||
| } | ||
|
|
||
| /// 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<QueryResult<'tcx>>>, | ||
| } |
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