From: lcnr <rust@lcnr.de>
Date: Wed, 8 Feb 2023 12:50:27 +0000 (+0100)
Subject: correctly update goals in the cache
X-Git-Url: https://git.lizzy.rs/?a=commitdiff_plain;h=a5164605bc3b572cf2281ce81ad5339fd6249aea;p=rust.git

correctly update goals in the cache
---

diff --git a/compiler/rustc_trait_selection/src/solve/search_graph/mod.rs b/compiler/rustc_trait_selection/src/solve/search_graph/mod.rs
index 7514c7ee551..a2ca4bc189c 100644
--- a/compiler/rustc_trait_selection/src/solve/search_graph/mod.rs
+++ b/compiler/rustc_trait_selection/src/solve/search_graph/mod.rs
@@ -7,7 +7,7 @@
 use overflow::OverflowData;
 use rustc_index::vec::IndexVec;
 use rustc_middle::ty::TyCtxt;
-use std::collections::hash_map::Entry;
+use std::{collections::hash_map::Entry, mem};
 
 rustc_index::newtype_index! {
     pub struct StackDepth {}
@@ -134,12 +134,15 @@ pub(super) fn try_finalize_goal(
         let provisional_entry_index = *cache.lookup_table.get(&goal).unwrap();
         let provisional_entry = &mut cache.entries[provisional_entry_index];
         let depth = provisional_entry.depth;
+        // We eagerly update the response in the cache here. If we have to reevaluate
+        // this goal we use the new response when hitting a cycle, and we definitely
+        // want to access the final response whenever we look at the cache.
+        let prev_response = mem::replace(&mut provisional_entry.response, response);
+
         // Was the current goal the root of a cycle and was the provisional response
         // different from the final one.
-        if has_been_used && provisional_entry.response != response {
-            // If so, update the provisional reponse for this goal...
-            provisional_entry.response = response;
-            // ...remove all entries whose result depends on this goal
+        if has_been_used && prev_response != response {
+            // If so, remove all entries whose result depends on this goal
             // from the provisional cache...
             //
             // That's not completely correct, as a nested goal can also