From d380d2877ed45cf1e75a87d822b30e4e1e21e3d4 Mon Sep 17 00:00:00 2001
From: Martin Leitner-Ankerl <martin.ankerl@gmail.com>
Date: Sun, 26 Mar 2023 15:19:43 +0200
Subject: [PATCH 1/4] bench: Add benchmark for prevector usage in std::vector

---
 src/bench/prevector.cpp | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/src/bench/prevector.cpp b/src/bench/prevector.cpp
index 59c4af086e..2524e215e4 100644
--- a/src/bench/prevector.cpp
+++ b/src/bench/prevector.cpp
@@ -80,6 +80,30 @@ static void PrevectorDeserialize(benchmark::Bench& bench)
     });
 }
 
+template <typename T>
+static void PrevectorFillVectorDirect(benchmark::Bench& bench)
+{
+    bench.run([&] {
+        std::vector<prevector<28, T>> vec;
+        for (size_t i = 0; i < 260; ++i) {
+            vec.emplace_back();
+        }
+    });
+}
+
+
+template <typename T>
+static void PrevectorFillVectorIndirect(benchmark::Bench& bench)
+{
+    bench.run([&] {
+        std::vector<prevector<28, T>> vec;
+        for (size_t i = 0; i < 260; ++i) {
+            // force allocation
+            vec.emplace_back(29, T{});
+        }
+    });
+}
+
 #define PREVECTOR_TEST(name)                                         \
     static void Prevector##name##Nontrivial(benchmark::Bench& bench) \
     {                                                                \
@@ -96,3 +120,5 @@ PREVECTOR_TEST(Clear)
 PREVECTOR_TEST(Destructor)
 PREVECTOR_TEST(Resize)
 PREVECTOR_TEST(Deserialize)
+PREVECTOR_TEST(FillVectorDirect)
+PREVECTOR_TEST(FillVectorIndirect)

From 81f67977f543faca2dcc35846f73e2917375ae79 Mon Sep 17 00:00:00 2001
From: Martin Leitner-Ankerl <martin.ankerl@gmail.com>
Date: Sun, 26 Mar 2023 15:39:20 +0200
Subject: [PATCH 2/4] util: prevector's move ctor and move assignment is
 `noexcept`

Move operations already are `noexcept`, so add the keyword to the methods.
This makes the `PrevectorFillVectorIndirect...` benchmarks about twice
as fast on my machine, because otherwise `std::vector` has to use a copy
when the vector resizes.
---
 src/prevector.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/prevector.h b/src/prevector.h
index f36cfe4ff6..d3e4b8fd0d 100644
--- a/src/prevector.h
+++ b/src/prevector.h
@@ -264,7 +264,7 @@ public:
         fill(item_ptr(0), other.begin(),  other.end());
     }
 
-    prevector(prevector<N, T, Size, Diff>&& other) {
+    prevector(prevector<N, T, Size, Diff>&& other) noexcept {
         swap(other);
     }
 
@@ -276,7 +276,7 @@ public:
         return *this;
     }
 
-    prevector& operator=(prevector<N, T, Size, Diff>&& other) {
+    prevector& operator=(prevector<N, T, Size, Diff>&& other) noexcept {
         swap(other);
         return *this;
     }

From fffc86f49f4eeb811b8438bc1b7f8d9e05882c6f Mon Sep 17 00:00:00 2001
From: Martin Leitner-Ankerl <martin.ankerl@gmail.com>
Date: Sun, 26 Mar 2023 15:39:53 +0200
Subject: [PATCH 3/4] test: CScriptCheck is used a lot in std::vector, make
 sure that's efficient

Adds a few static_asserts so CScriptCheck stays is_nothrow_move_assignable,
is_nothrow_move_constructible, and is_nothrow_destructible
---
 src/validation.h | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/src/validation.h b/src/validation.h
index aba863db09..b6d1995c5b 100644
--- a/src/validation.h
+++ b/src/validation.h
@@ -42,6 +42,7 @@
 #include <stdint.h>
 #include <string>
 #include <thread>
+#include <type_traits>
 #include <utility>
 #include <vector>
 
@@ -331,6 +332,11 @@ public:
     ScriptError GetScriptError() const { return error; }
 };
 
+// CScriptCheck is used a lot in std::vector, make sure that's efficient
+static_assert(std::is_nothrow_move_assignable_v<CScriptCheck>);
+static_assert(std::is_nothrow_move_constructible_v<CScriptCheck>);
+static_assert(std::is_nothrow_destructible_v<CScriptCheck>);
+
 /** Initializes the script-execution cache */
 [[nodiscard]] bool InitScriptExecutionCache(size_t max_size_bytes);
 

From bfb9291a8661fe5b26c14ed755cfa89d27c37110 Mon Sep 17 00:00:00 2001
From: Martin Leitner-Ankerl <martin.ankerl@gmail.com>
Date: Sun, 26 Mar 2023 14:40:32 +0200
Subject: [PATCH 4/4] util: implement prevector's move ctor & move assignment

Using swap() was rather wasteful because it had to copy the whole direct
memory data twice. Also, due to the swap() in move assignment the moved-from
object might hold on to unused memory for longer than necessary.
---
 src/prevector.h | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/src/prevector.h b/src/prevector.h
index d3e4b8fd0d..bcab1ff00c 100644
--- a/src/prevector.h
+++ b/src/prevector.h
@@ -264,8 +264,10 @@ public:
         fill(item_ptr(0), other.begin(),  other.end());
     }
 
-    prevector(prevector<N, T, Size, Diff>&& other) noexcept {
-        swap(other);
+    prevector(prevector<N, T, Size, Diff>&& other) noexcept
+        : _union(std::move(other._union)), _size(other._size)
+    {
+        other._size = 0;
     }
 
     prevector& operator=(const prevector<N, T, Size, Diff>& other) {
@@ -277,7 +279,12 @@ public:
     }
 
     prevector& operator=(prevector<N, T, Size, Diff>&& other) noexcept {
-        swap(other);
+        if (!is_direct()) {
+            free(_union.indirect_contents.indirect);
+        }
+        _union = std::move(other._union);
+        _size = other._size;
+        other._size = 0;
         return *this;
     }