the coolest beans

compiler/rustc_next_trait_solver/src/solve/search_graph.rs

@@ -39,6 +39,7 @@ where
         inspect.is_noop()
     }
 
+    const DIVIDE_AVAILABLE_DEPTH_ON_OVERFLOW: usize = 4;
     fn recursion_limit(cx: I) -> usize {
         cx.recursion_limit()
     }

compiler/rustc_type_ir/src/search_graph/mod.rs

@@ -66,6 +66,7 @@ pub trait Delegate {
     type ProofTreeBuilder;
     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(
@@ -150,7 +151,7 @@ impl AvailableDepth {
             }
 
             Some(if last.encountered_overflow {
-                AvailableDepth(last.available_depth.0 / 2)
+                AvailableDepth(last.available_depth.0 / D::DIVIDE_AVAILABLE_DEPTH_ON_OVERFLOW)
             } else {
                 AvailableDepth(last.available_depth.0 - 1)
             })
@@ -306,7 +307,7 @@ struct StackEntry<X: Cx> {
 /// goals still on the stack.
 #[derive_where(Debug; X: Cx)]
 struct ProvisionalCacheEntry<X: Cx> {
-    is_sus: bool,
+    encountered_overflow: bool,
     heads: CycleHeads,
     path_from_head: CycleKind,
     nested_goals: NestedGoals<X>,
@@ -421,7 +422,7 @@ impl<D: Delegate<Cx = X>, X: Cx> SearchGraph<D> {
         self.provisional_cache.retain(|&input, entries| {
             entries.retain_mut(|entry| {
                 let ProvisionalCacheEntry {
-                    is_sus: _,
+                    encountered_overflow: _,
                     heads,
                     path_from_head,
                     nested_goals,
@@ -544,10 +545,9 @@ impl<D: Delegate<Cx = X>, X: Cx> SearchGraph<D> {
             debug_assert!(validate_cache.is_none());
             let entry = self.provisional_cache.entry(input).or_default();
             let StackEntry { heads, nested_goals, encountered_overflow, .. } = final_entry;
-            let is_sus = encountered_overflow;
             let path_from_head = Self::stack_path_kind(cx, &self.stack, heads.highest_cycle_head());
             entry.push(ProvisionalCacheEntry {
-                is_sus,
+                encountered_overflow,
                 heads,
                 path_from_head,
                 nested_goals,
@@ -606,14 +606,18 @@ impl<D: Delegate<Cx = X>, X: Cx> SearchGraph<D> {
             debug!(?input, ?path_from_global_entry, ?entries, "candidate_is_applicable");
             // A provisional cache entry is applicable if the path to
             // its highest cycle head is equal to the expected path.
-            for ProvisionalCacheEntry {
-                is_sus: _,
-                heads,
+            for &ProvisionalCacheEntry {
+                encountered_overflow,
+                ref heads,
                 path_from_head,
                 nested_goals: _,
                 result: _,
-            } in entries.iter().filter(|e| !e.is_sus)
+            } in entries.iter()
             {
+                if encountered_overflow {
+                    continue;
+                }
+
                 let head = heads.highest_cycle_head();
                 let full_path = if Self::stack_coinductive_from(cx, stack, head) {
                     path_from_global_entry
@@ -707,15 +711,15 @@ impl<D: Delegate<Cx = X>, X: Cx> SearchGraph<D> {
 
         let entries = self.provisional_cache.get(&input)?;
         for &ProvisionalCacheEntry {
-            is_sus,
+            encountered_overflow,
             ref heads,
             path_from_head,
             ref nested_goals,
             result,
         } in entries
         {
             let head = heads.highest_cycle_head();
-            if is_sus {
+            if encountered_overflow {
                 let last = self.stack.raw.last().unwrap();
                 if !last.heads.opt_lowest_cycle_head().is_some_and(|lowest| lowest <= head) {
                     continue;