Auto merge of #155550 - zetanumbers:cache_insert_unique, r=oli-obk

Replace `ShardedHashMap` method `insert` with debug-checked `insert_unique`

Currently every use of `ShardedHashMap::insert` checks that it won't evict an old value due to unique key. I haven't found any issue related to that faulty condition, so I thought of replacing it with `ShardedHashMap::insert_unique` which doesn't check for this condition unless `debug_assertions` are enabled. This might improve the performance.

r? @petrochenkov

Author: bors

compiler/rustc_data_structures/src/sharded.rs

@@ -1,6 +1,6 @@
 use std::borrow::Borrow;
 use std::hash::{Hash, Hasher};
-use std::{iter, mem};
+use std::iter;
 
 use either::Either;
 use hashbrown::hash_table::{self, Entry, HashTable};
@@ -183,19 +183,27 @@ impl<K: Eq + Hash, V> ShardedHashMap<K, V> {
         }
     }
 
+    /// Insert value into the [`ShardedHashMap`] with unique key.
+    ///
+    /// This function panics if debug_assertions are enabled and uniqueness is violated.
+    /// If uniqueness is violated but debug_assertions are disabled then lookups will arbitrarily
+    /// return one of the inserted elements.
     #[inline]
-    pub fn insert(&self, key: K, value: V) -> Option<V> {
+    pub fn insert_unique(&self, key: K, value: V) {
         let hash = make_hash(&key);
         let mut shard = self.lock_shard_by_hash(hash);
 
-        match table_entry(&mut shard, hash, &key) {
-            Entry::Occupied(e) => {
-                let previous = mem::replace(&mut e.into_mut().1, value);
-                Some(previous)
+        cfg_select! {
+            debug_assertions => match table_entry(&mut shard, hash, &key) {
+                Entry::Occupied(_) => {
+                    panic!("tried to insert key that's already present");
+                }
+                Entry::Vacant(e) => {
+                    e.insert((key, value));
+                }
             }
-            Entry::Vacant(e) => {
-                e.insert((key, value));
-                None
+            _ => {
+                shard.insert_unique(hash, (key, value), |(k, _)| make_hash(k));
             }
         }
     }

compiler/rustc_middle/src/mir/interpret/mod.rs

@@ -473,9 +473,8 @@ impl<'tcx> TyCtxt<'tcx> {
         }
         let id = self.alloc_map.reserve();
         debug!("creating alloc {:?} with id {id:?}", alloc_salt.0);
-        let had_previous = self.alloc_map.to_alloc.insert(id, alloc_salt.0.clone()).is_some();
         // We just reserved, so should always be unique.
-        assert!(!had_previous);
+        self.alloc_map.to_alloc.insert_unique(id, alloc_salt.0.clone());
         dedup.insert(alloc_salt, id);
         id
     }
@@ -548,21 +547,17 @@ impl<'tcx> TyCtxt<'tcx> {
     }
 
     /// Freezes an `AllocId` created with `reserve` by pointing it at an `Allocation`. Trying to
-    /// call this function twice, even with the same `Allocation` will ICE the compiler.
+    /// call this function twice, even with the same `Allocation` will ICE the compiler if
+    /// debug_assertions are enabled.
     pub fn set_alloc_id_memory(self, id: AllocId, mem: ConstAllocation<'tcx>) {
-        if let Some(old) = self.alloc_map.to_alloc.insert(id, GlobalAlloc::Memory(mem)) {
-            bug!("tried to set allocation ID {id:?}, but it was already existing as {old:#?}");
-        }
+        self.alloc_map.to_alloc.insert_unique(id, GlobalAlloc::Memory(mem))
     }
 
     /// Freezes an `AllocId` created with `reserve` by pointing it at a static item. Trying to
-    /// call this function twice, even with the same `DefId` will ICE the compiler.
+    /// call this function twice, even with the same `DefId` will ICE the compiler if
+    /// debug_assertions are enabled.
     pub fn set_nested_alloc_id_static(self, id: AllocId, def_id: LocalDefId) {
-        if let Some(old) =
-            self.alloc_map.to_alloc.insert(id, GlobalAlloc::Static(def_id.to_def_id()))
-        {
-            bug!("tried to set allocation ID {id:?}, but it was already existing as {old:#?}");
-        }
+        self.alloc_map.to_alloc.insert_unique(id, GlobalAlloc::Static(def_id.to_def_id()))
     }
 }
 

compiler/rustc_middle/src/query/caches.rs

@@ -65,9 +65,7 @@ where
 
     #[inline]
     fn complete(&self, key: K, value: V, index: DepNodeIndex) {
-        // We may be overwriting another value. This is all right, since the dep-graph
-        // will check that the value fingerprint matches.
-        self.cache.insert(key, (value, index));
+        self.cache.insert_unique(key, (value, index));
     }
 
     fn for_each(&self, f: &mut dyn FnMut(&Self::Key, &Self::Value, DepNodeIndex)) {