Speed up `raw_hash_map::[]` with ABSL hardening enabled by unchecking dereference of iterator returned by `try_emplace`.

PiperOrigin-RevId: 597920257
Change-Id: I1b2e8f10a2f1efa763a6f0760294beafdb6fd9c0

1 files changed, 9 insertions, 2 deletions

diff --git a/absl/container/internal/raw_hash_map.h b/absl/container/internal/raw_hash_map.h
index c1d4d4bc..97182bc7 100644
--- a/absl/container/internal/raw_hash_map.h
+++ b/absl/container/internal/raw_hash_map.h
@@ -177,13 +177,20 @@ class raw_hash_map : public raw_hash_set<Policy, Hash, Eq, Alloc> {
   template <class K = key_type, class P = Policy, K* = nullptr>
   MappedReference<P> operator[](key_arg<K>&& key)
       ABSL_ATTRIBUTE_LIFETIME_BOUND {
-    return Policy::value(&*try_emplace(std::forward<K>(key)).first);
+    // It is safe to use unchecked_deref here because try_emplace
+    // will always return an iterator pointing to a valid item in the table,
+    // since it inserts if nothing is found for the given key.
+    return Policy::value(
+        &this->unchecked_deref(try_emplace(std::forward<K>(key)).first));
   }
 
   template <class K = key_type, class P = Policy>
   MappedReference<P> operator[](const key_arg<K>& key)
       ABSL_ATTRIBUTE_LIFETIME_BOUND {
-    return Policy::value(&*try_emplace(key).first);
+    // It is safe to use unchecked_deref here because try_emplace
+    // will always return an iterator pointing to a valid item in the table,
+    // since it inserts if nothing is found for the given key.
+    return Policy::value(&this->unchecked_deref(try_emplace(key).first));
   }
 
  private: