From fa994d0377ddc7a10b760a5bde75239d76b7f1e7 Mon Sep 17 00:00:00 2001
From: Billy Donahue <billy.donahue@mongodb.com>
Date: Wed, 17 May 2023 07:57:56 +0000
Subject: SERVER-76788 elide trivial Decoration constructors

---
 src/mongo/util/decoration_container.h |  2 +-
 src/mongo/util/decoration_registry.h  | 14 ++++++++++++--
 2 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/src/mongo/util/decoration_container.h b/src/mongo/util/decoration_container.h
index 4b2f7bf0619..67a76730a16 100644
--- a/src/mongo/util/decoration_container.h
+++ b/src/mongo/util/decoration_container.h
@@ -97,7 +97,7 @@ public:
     explicit DecorationContainer(Decorable<DecoratedType>* const decorated,
                                  const DecorationRegistry<DecoratedType>* const registry)
         : _registry(registry),
-          _decorationData(new unsigned char[registry->getDecorationBufferSizeBytes()]) {
+          _decorationData(new unsigned char[registry->getDecorationBufferSizeBytes()]{}) {
         // Because the decorations live in the externally allocated storage buffer at
         // `_decorationData`, there needs to be a way to get back from a known location within this
         // buffer to the type which owns those decorations.  We place a pointer to ourselves, a
diff --git a/src/mongo/util/decoration_registry.h b/src/mongo/util/decoration_registry.h
index 4720d5fc9ed..5bac5979830 100644
--- a/src/mongo/util/decoration_registry.h
+++ b/src/mongo/util/decoration_registry.h
@@ -71,7 +71,7 @@ public:
             typename DecorationContainer<DecoratedType>::template DecorationDescriptorWithType<T>(
                 std::move(declareDecoration(sizeof(T),
                                             std::alignment_of<T>::value,
-                                            &constructAt<T>,
+                                            getConstructorFn<T>(),
                                             nullptr,
                                             nullptr,
                                             getDestructorFn<T>())));
@@ -93,7 +93,7 @@ public:
             typename DecorationContainer<DecoratedType>::template DecorationDescriptorWithType<T>(
                 std::move(declareDecoration(sizeof(T),
                                             std::alignment_of<T>::value,
-                                            &constructAt<T>,
+                                            getConstructorFn<T>(),
                                             &copyConstructAt<T>,
                                             &copyAssignAt<T>,
                                             getDestructorFn<T>())));
@@ -131,6 +131,8 @@ public:
         using std::cend;
 
         for (; iter != cend(_decorationInfo); ++iter) {
+            if (!iter->constructor)
+                continue;
             iter->constructor(container->getDecoration(iter->descriptor));
         }
 
@@ -270,6 +272,14 @@ private:
         static_cast<T*>(location)->~T();
     }
 
+    template <typename T>
+    static constexpr DecorationConstructorFn getConstructorFn() {
+        if constexpr (std::is_trivially_constructible_v<T>)
+            return nullptr;
+        else
+            return &constructAt<T>;
+    }
+
     template <typename T>
     static constexpr DecorationDestructorFn getDestructorFn() {
         if constexpr (std::is_trivially_destructible_v<T>)
-- 
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