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lcnr 2025-06-17 10:27:31 +02:00
parent 2e57845de7
commit 8710c1fec9
1 changed files with 7 additions and 9 deletions
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16
compiler/rustc_type_ir/src/search_graph/mod.rs
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@ -381,18 +381,16 @@ impl PathsToNested {
/// The nested goals of each stack entry and the path from the
/// stack entry to that nested goal.
///
/// They are used when checking whether reevaluating a global cache
/// would encounter a cycle or use a provisional cache entry given the
/// currentl search graph state. We need to disable the global cache
/// in this case as it could otherwise result in behaviorial differences.
/// Cycles can impact behavior. The cycle ABA may have different final
/// results from a the cycle BAB depending on the cycle root.
///
/// We only start tracking nested goals once we've either encountered
/// overflow or a solver cycle. This is a performance optimization to
/// avoid tracking nested goals on the happy path.
///
/// We use nested goals for two reasons:
/// - when rebasing provisional cache entries
/// - when checking whether we have to ignore a global cache entry as reevaluating
/// it would encounter a cycle or use a provisional cache entry.
///
/// We need to disable the global cache if using it would hide a cycle, as
/// cycles can impact behavior. The cycle ABA may have different final
/// results from a the cycle BAB depending on the cycle root.
#[derive_where(Debug, Default, Clone; X: Cx)]
struct NestedGoals<X: Cx> {
nested_goals: HashMap<X::Input, PathsToNested>,