edc3dc6abd
As a follow-up to #121013 (which focused on `std::ranges::copy`), this PR optimizes the performance of `std::ranges::copy_backward` for `vector<bool>::iterator`, addressing a subtask outlined in issue #64038. The optimizations yield performance improvements of up to 2000x for aligned copies and 60x for unaligned copies.
138 lines
4.2 KiB
C++
138 lines
4.2 KiB
C++
//===----------------------------------------------------------------------===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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// <algorithm>
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// template<BidirectionalIterator InIter, BidirectionalIterator OutIter>
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// requires OutputIterator<OutIter, InIter::reference>
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// constexpr OutIter // constexpr after C++17
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// copy_backward(InIter first, InIter last, OutIter result);
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#include <algorithm>
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#include <cassert>
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#include <vector>
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#include "test_macros.h"
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#include "test_iterators.h"
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#include "user_defined_integral.h"
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class PaddedBase {
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public:
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TEST_CONSTEXPR PaddedBase(std::int16_t a, std::int8_t b) : a_(a), b_(b) {}
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std::int16_t a_;
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std::int8_t b_;
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};
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class Derived : public PaddedBase {
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public:
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TEST_CONSTEXPR Derived(std::int16_t a, std::int8_t b, std::int8_t c) : PaddedBase(a, b), c_(c) {}
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std::int8_t c_;
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};
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template <class InIter, class OutIter>
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TEST_CONSTEXPR_CXX20 void test_copy_backward() {
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{
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const unsigned N = 1000;
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int ia[N] = {};
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for (unsigned i = 0; i < N; ++i)
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ia[i] = i;
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int ib[N] = {0};
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OutIter r = std::copy_backward(InIter(ia), InIter(ia + N), OutIter(ib + N));
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assert(base(r) == ib);
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for (unsigned i = 0; i < N; ++i)
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assert(ia[i] == ib[i]);
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}
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}
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TEST_CONSTEXPR_CXX20 bool test_vector_bool(std::size_t N) {
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std::vector<bool> in(N, false);
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for (std::size_t i = 0; i < N; i += 2)
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in[i] = true;
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{ // Test copy_backward with aligned bytes
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std::vector<bool> out(N);
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std::copy_backward(in.begin(), in.end(), out.end());
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assert(in == out);
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}
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{ // Test copy_backward with unaligned bytes
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std::vector<bool> out(N + 8);
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std::copy_backward(in.begin(), in.end(), out.end() - 4);
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for (std::size_t i = 0; i < N; ++i)
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assert(out[i + 4] == in[i]);
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}
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return true;
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};
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TEST_CONSTEXPR_CXX20 bool test() {
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test_copy_backward<bidirectional_iterator<const int*>, bidirectional_iterator<int*> >();
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test_copy_backward<bidirectional_iterator<const int*>, random_access_iterator<int*> >();
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test_copy_backward<bidirectional_iterator<const int*>, int*>();
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test_copy_backward<random_access_iterator<const int*>, bidirectional_iterator<int*> >();
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test_copy_backward<random_access_iterator<const int*>, random_access_iterator<int*> >();
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test_copy_backward<random_access_iterator<const int*>, int*>();
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test_copy_backward<const int*, bidirectional_iterator<int*> >();
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test_copy_backward<const int*, random_access_iterator<int*> >();
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test_copy_backward<const int*, int*>();
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#if TEST_STD_VER > 17
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test_copy_backward<contiguous_iterator<const int*>, bidirectional_iterator<int*>>();
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test_copy_backward<contiguous_iterator<const int*>, random_access_iterator<int*>>();
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test_copy_backward<contiguous_iterator<const int*>, int*>();
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test_copy_backward<bidirectional_iterator<const int*>, contiguous_iterator<int*>>();
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test_copy_backward<random_access_iterator<const int*>, contiguous_iterator<int*>>();
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test_copy_backward<contiguous_iterator<const int*>, contiguous_iterator<int*>>();
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test_copy_backward<const int*, contiguous_iterator<int*>>();
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#endif
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{ // Make sure that padding bits aren't copied
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Derived src(1, 2, 3);
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Derived dst(4, 5, 6);
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std::copy_backward(
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static_cast<PaddedBase*>(&src), static_cast<PaddedBase*>(&src) + 1, static_cast<PaddedBase*>(&dst) + 1);
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assert(dst.a_ == 1);
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assert(dst.b_ == 2);
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assert(dst.c_ == 6);
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}
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{ // Make sure that overlapping ranges can be copied
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int a[] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
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std::copy_backward(a, a + 7, a + 10);
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int expected[] = {1, 2, 3, 1, 2, 3, 4, 5, 6, 7};
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assert(std::equal(a, a + 10, expected));
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}
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{ // Test vector<bool>::iterator optimization
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assert(test_vector_bool(8));
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assert(test_vector_bool(19));
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assert(test_vector_bool(32));
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assert(test_vector_bool(49));
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assert(test_vector_bool(64));
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assert(test_vector_bool(199));
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assert(test_vector_bool(256));
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}
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return true;
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}
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int main(int, char**) {
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test();
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#if TEST_STD_VER > 17
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static_assert(test());
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#endif
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return 0;
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}
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