Speed up `raw_hash_set::contains()` when ABSL hardening is enabled by removing…

Speed up `raw_hash_set::contains()` when ABSL hardening is enabled by removing the iterator invalidation check from the comparison that contains performs.

PiperOrigin-RevId: 595460301
Change-Id: I9a5d6c81385e38184f4848c58209adc5d32bb7be

absl/container/internal/raw_hash_set.h

@@ -2016,6 +2016,12 @@ class raw_hash_set {
     union {
       slot_type* slot_;
     };
+
+    // An equality check which skips ABSL Hardening iterator invalidation
+    // checks.
+    // Should be used when the lifetimes of the iterators are well-enough
+    // understood to prove that they cannot be invalid.
+    bool unchecked_equals(const iterator& b) { return ctrl_ == b.control(); }
   };
 
   class const_iterator {
@@ -2060,6 +2066,10 @@ class raw_hash_set {
     slot_type* slot() const { return inner_.slot(); }
 
     iterator inner_;
+
+    bool unchecked_equals(const const_iterator& b) {
+      return inner_.unchecked_equals(b.inner_);
+    }
   };
 
   using node_type = node_handle<Policy, hash_policy_traits<Policy>, Alloc>;
@@ -2707,7 +2717,11 @@ class raw_hash_set {
 
   template <class K = key_type>
   bool contains(const key_arg<K>& key) const {
-    return find(key) != end();
+    // Here neither the iterator returned by `find()` nor `end()` can be invalid
+    // outside of potential thread-safety issues.
+    // `find()`'s return value is constructed, used, and then destructed
+    // all in this context.
+    return !find(key).unchecked_equals(end());
   }
 
   template <class K = key_type>