Speed up `raw_hash_map::[]` with ABSL hardening enabled by unchecking dereference of iterator returned by `try_emplace`.
PiperOrigin-RevId: 597920257
Change-Id: I1b2e8f10a2f1efa763a6f0760294beafdb6fd9c0
diff --git a/absl/container/internal/raw_hash_map.h b/absl/container/internal/raw_hash_map.h
index c1d4d4b..97182bc 100644
--- a/absl/container/internal/raw_hash_map.h
+++ b/absl/container/internal/raw_hash_map.h
@@ -177,13 +177,20 @@
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:
diff --git a/absl/container/internal/raw_hash_set.h b/absl/container/internal/raw_hash_set.h
index b6dc754..3518bc3 100644
--- a/absl/container/internal/raw_hash_set.h
+++ b/absl/container/internal/raw_hash_set.h
@@ -1943,7 +1943,7 @@
// PRECONDITION: not an end() iterator.
reference operator*() const {
AssertIsFull(ctrl_, generation(), generation_ptr(), "operator*()");
- return PolicyTraits::element(slot_);
+ return unchecked_deref();
}
// PRECONDITION: not an end() iterator.
@@ -2023,6 +2023,10 @@
// 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(); }
+
+ // Dereferences the iterator without ABSL Hardening iterator invalidation
+ // checks.
+ reference unchecked_deref() const { return PolicyTraits::element(slot_); }
};
class const_iterator {
@@ -3159,6 +3163,8 @@
return {control() + i, slot_array() + i, common().generation_ptr()};
}
+ reference unchecked_deref(iterator it) { return it.unchecked_deref(); }
+
private:
friend struct RawHashSetTestOnlyAccess;
