[Core] Prevector Optimizations

src/Makefile.bench.include

@@ -13,7 +13,7 @@ bench_bench_pivx_SOURCES = \
   bench/crypto_hash.cpp \
   bench/perf.cpp \
   bench/perf.h \
-  bench/prevector_destructor.cpp
+  bench/prevector.cpp
 
 bench_bench_pivx_CPPFLAGS = $(AM_CPPFLAGS) $(BITCOIN_INCLUDES) $(EVENT_CFLAGS) $(EVENT_PTHREADS_CFLAGS) -I$(builddir)/bench/
 bench_bench_pivx_CXXFLAGS = $(AM_CXXFLAGS) $(PIE_FLAGS)

src/bench/prevector.cpp

@@ -0,0 +1,89 @@
+// Copyright (c) 2015-2017 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include "bench/bench.h"
+
+#include "compat.h"
+#include "prevector.h"
+#include "serialize.h"
+#include "streams.h"
+
+#include <type_traits>
+
+// GCC 4.8 is missing some C++11 type_traits,
+// https://www.gnu.org/software/gcc/gcc-5/changes.html
+#if defined(__GNUC__) && !defined(__clang__) && __GNUC__ < 5
+#define IS_TRIVIALLY_CONSTRUCTIBLE std::has_trivial_default_constructor
+#else
+#define IS_TRIVIALLY_CONSTRUCTIBLE std::is_trivially_default_constructible
+#endif
+
+struct nontrivial_t {
+    int x;
+    nontrivial_t() :x(-1) {}
+};
+static_assert(!IS_TRIVIALLY_CONSTRUCTIBLE<nontrivial_t>::value,
+              "expected nontrivial_t to not be trivially constructible");
+
+typedef unsigned char trivial_t;
+static_assert(IS_TRIVIALLY_CONSTRUCTIBLE<trivial_t>::value,
+              "expected trivial_t to be trivially constructible");
+
+template <typename T>
+static void PrevectorDestructor(benchmark::State& state)
+{
+    while (state.KeepRunning()) {
+        for (auto x = 0; x < 1000; ++x) {
+            prevector<28, T> t0;
+            prevector<28, T> t1;
+            t0.resize(28);
+            t1.resize(29);
+        }
+    }
+}
+
+template <typename T>
+static void PrevectorClear(benchmark::State& state)
+{
+
+    while (state.KeepRunning()) {
+        for (auto x = 0; x < 1000; ++x) {
+            prevector<28, T> t0;
+            prevector<28, T> t1;
+            t0.resize(28);
+            t0.clear();
+            t1.resize(29);
+            t0.clear();
+        }
+    }
+}
+
+template <typename T>
+void PrevectorResize(benchmark::State& state)
+{
+    while (state.KeepRunning()) {
+        prevector<28, T> t0;
+        prevector<28, T> t1;
+        for (auto x = 0; x < 1000; ++x) {
+            t0.resize(28);
+            t0.resize(0);
+            t1.resize(29);
+            t1.resize(0);
+        }
+    }
+}
+
+#define PREVECTOR_TEST(name)                                               \
+    static void Prevector ## name ## Nontrivial(benchmark::State& state) { \
+        PrevectorResize<nontrivial_t>(state);                              \
+    }                                                                      \
+    BENCHMARK(Prevector ## name ## Nontrivial);                            \
+    static void Prevector ## name ## Trivial(benchmark::State& state) {    \
+        PrevectorResize<trivial_t>(state);                                 \
+    }                                                                      \
+    BENCHMARK(Prevector ## name ## Trivial);
+
+PREVECTOR_TEST(Clear)
+PREVECTOR_TEST(Destructor)
+PREVECTOR_TEST(Resize)

src/prevector.h

@@ -10,6 +10,8 @@
 #include <stdint.h>
 #include <string.h>
 
+#include <algorithm>
+#include <cstddef>
 #include <iterator>
 #include <type_traits>
 
@@ -194,16 +196,27 @@ class prevector {
     T* item_ptr(difference_type pos) { return is_direct() ? direct_ptr(pos) : indirect_ptr(pos); }
     const T* item_ptr(difference_type pos) const { return is_direct() ? direct_ptr(pos) : indirect_ptr(pos); }
 
+    void fill(T* dst, ptrdiff_t count, const T& value = T{}) {
+        std::fill_n(dst, count, value);
+    }
+
+    template<typename InputIterator>
+    void fill(T* dst, InputIterator first, InputIterator last) {
+        while (first != last) {
+            new(static_cast<void*>(dst)) T(*first);
+            ++dst;
+            ++first;
+        }
+    }
+
 public:
     void assign(size_type n, const T& val) {
         clear();
         if (capacity() < n) {
             change_capacity(n);
         }
-        while (size() < n) {
-            _size++;
-            new(static_cast<void*>(item_ptr(size() - 1))) T(val);
-        }
+        _size += n;
+        fill(item_ptr(0), n, val);
     }
 
     template<typename InputIterator>
@@ -213,11 +226,8 @@ class prevector {
         if (capacity() < n) {
             change_capacity(n);
         }
-        while (first != last) {
-            _size++;
-            new(static_cast<void*>(item_ptr(size() - 1))) T(*first);
-            ++first;
-        }
+        _size += n;
+        fill(item_ptr(0), first, last);
     }
 
     prevector() {}
@@ -228,31 +238,23 @@ class prevector {
 
     explicit prevector(size_type n, const T& val = T()) {
         change_capacity(n);
-        while (size() < n) {
-            _size++;
-            new(static_cast<void*>(item_ptr(size() - 1))) T(val);
-        }
+        _size += n;
+        fill(item_ptr(0), n, val);
     }
 
     template<typename InputIterator>
     prevector(InputIterator first, InputIterator last) {
         size_type n = last - first;
         change_capacity(n);
-        while (first != last) {
-            _size++;
-            new(static_cast<void*>(item_ptr(size() - 1))) T(*first);
-            ++first;
-        }
+        _size += n;
+        fill(item_ptr(0), first, last);
     }
 
     prevector(const prevector<N, T, Size, Diff>& other) {
-        change_capacity(other.size());
-        const_iterator it = other.begin();
-        while (it != other.end()) {
-            _size++;
-            new(static_cast<void*>(item_ptr(size() - 1))) T(*it);
-            ++it;
-        }
+        size_type n = other.size();
+        change_capacity(n);
+        _size += n;
+        fill(item_ptr(0), other.begin(),  other.end());
     }
 
     prevector(prevector<N, T, Size, Diff>&& other) {
@@ -263,14 +265,7 @@ class prevector {
         if (&other == this) {
             return *this;
         }
-        resize(0);
-        change_capacity(other.size());
-        const_iterator it = other.begin();
-        while (it != other.end()) {
-            _size++;
-            new(static_cast<void*>(item_ptr(size() - 1))) T(*it);
-            ++it;
-        }
+        assign(other.begin(), other.end());
         return *this;
     }
 
@@ -314,16 +309,20 @@ class prevector {
     }
 
     void resize(size_type new_size) {
-        if (size() > new_size) {
+        size_type cur_size = size();
+        if (cur_size == new_size) {
+            return;
+        }
+        if (cur_size > new_size) {
             erase(item_ptr(new_size), end());
+            return;
         }
         if (new_size > capacity()) {
             change_capacity(new_size);
         }
-        while (size() < new_size) {
-            _size++;
-            new(static_cast<void*>(item_ptr(size() - 1))) T();
-        }
+        ptrdiff_t increase = new_size - cur_size;
+        fill(item_ptr(cur_size), increase);
+        _size += increase;
     }
 
     void reserve(size_type new_capacity) {
@@ -346,10 +345,11 @@ class prevector {
         if (capacity() < new_size) {
             change_capacity(new_size + (new_size >> 1));
         }
-        memmove(item_ptr(p + 1), item_ptr(p), (size() - p) * sizeof(T));
+        T* ptr = item_ptr(p);
+        memmove(ptr + 1, ptr, (size() - p) * sizeof(T));
         _size++;
-        new(static_cast<void*>(item_ptr(p))) T(value);
-        return iterator(item_ptr(p));
+        new(static_cast<void*>(ptr)) T(value);
+        return iterator(ptr);
     }
 
     void insert(iterator pos, size_type count, const T& value) {
@@ -358,11 +358,10 @@ class prevector {
         if (capacity() < new_size) {
             change_capacity(new_size + (new_size >> 1));
         }
-        memmove(item_ptr(p + count), item_ptr(p), (size() - p) * sizeof(T));
+        T* ptr = item_ptr(p);
+        memmove(ptr + count, ptr, (size() - p) * sizeof(T));
         _size += count;
-        for (size_type i = 0; i < count; i++) {
-            new(static_cast<void*>(item_ptr(p + i))) T(value);
-        }
+        fill(item_ptr(p), count, value);
     }
 
     template<typename InputIterator>