Early return from destroy_slots for trivially destructible types in flat_hash_{*}.

PiperOrigin-RevId: 602813933
Change-Id: I744fe438281755a141b2fd47e54ab9c6c0fad5a3

1 files changed, 10 insertions, 2 deletions

diff --git a/absl/container/internal/common_policy_traits.h b/absl/container/internal/common_policy_traits.h
index 57eac678..77df4790 100644
--- a/absl/container/internal/common_policy_traits.h
+++ b/absl/container/internal/common_policy_traits.h
@@ -45,9 +45,10 @@ struct common_policy_traits {
 
   // PRECONDITION: `slot` is INITIALIZED
   // POSTCONDITION: `slot` is UNINITIALIZED
+  // Returns std::true_type in case destroy is trivial.
   template <class Alloc>
-  static void destroy(Alloc* alloc, slot_type* slot) {
-    Policy::destroy(alloc, slot);
+  static auto destroy(Alloc* alloc, slot_type* slot) {
+    return Policy::destroy(alloc, slot);
   }
 
   // Transfers the `old_slot` to `new_slot`. Any memory allocated by the
@@ -86,6 +87,13 @@ struct common_policy_traits {
                         std::true_type>::value;
   }
 
+  // Returns true if destroy is trivial and can be omitted.
+  template <class Alloc>
+  static constexpr bool destroy_is_trivial() {
+    return std::is_same<decltype(destroy<Alloc>(nullptr, nullptr)),
+                        std::true_type>::value;
+  }
+
  private:
   // To rank the overloads below for overload resolution. Rank0 is preferred.
   struct Rank2 {};