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[libc++] Simplify vector<bool> fill constructors #160521

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Merged
merged 1 commit into from
Sep 25, 2025
Merged

[libc++] Simplify vector<bool> fill constructors #160521

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27 changes: 8 additions & 19 deletions libcxx/include/__vector/vector_bool.h
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Original file line number Diff line number Diff line change
Expand Up @@ -478,7 +478,6 @@ class vector<bool, _Allocator> {
return (__new_size + (__bits_per_word - 1)) & ~((size_type)__bits_per_word - 1);
}
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 size_type __recommend(size_type __new_size) const;
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void __construct_at_end(size_type __n, bool __x);
template <class _InputIterator, class _Sentinel>
_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void
__construct_at_end(_InputIterator __first, _Sentinel __last, size_type __n);
Expand Down Expand Up @@ -567,20 +566,6 @@ vector<bool, _Allocator>::__recommend(size_type __new_size) const {
return std::max<size_type>(2 * __cap, __align_it(__new_size));
}

// Default constructs __n objects starting at __end_
// Precondition: size() + __n <= capacity()
// Postcondition: size() == size() + __n
template <class _Allocator>
inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void
vector<bool, _Allocator>::__construct_at_end(size_type __n, bool __x) {
_LIBCPP_ASSERT_INTERNAL(
capacity() >= size() + __n, "vector<bool>::__construct_at_end called with insufficient capacity");
std::fill_n(end(), __n, __x);
this->__size_ += __n;
if (end().__ctz_ != 0) // Ensure uninitialized leading bits in the last word are set to zero
std::fill_n(end(), __bits_per_word - end().__ctz_, 0);
}

template <class _Allocator>
template <class _InputIterator, class _Sentinel>
_LIBCPP_CONSTEXPR_SINCE_CXX20 void
Expand Down Expand Up @@ -613,7 +598,8 @@ _LIBCPP_CONSTEXPR_SINCE_CXX20 vector<bool, _Allocator>::vector(size_type __n)
: __begin_(nullptr), __size_(0), __cap_(0) {
if (__n > 0) {
__vallocate(__n);
__construct_at_end(__n, false);
std::fill_n(__begin_, __external_cap_to_internal(__n), __storage_type(0));
__size_ = __n;
}
}

Expand All @@ -623,7 +609,8 @@ _LIBCPP_CONSTEXPR_SINCE_CXX20 vector<bool, _Allocator>::vector(size_type __n, co
: __begin_(nullptr), __size_(0), __cap_(0), __alloc_(static_cast<__storage_allocator>(__a)) {
if (__n > 0) {
__vallocate(__n);
__construct_at_end(__n, false);
std::fill_n(__begin_, __external_cap_to_internal(__n), __storage_type(0));
__size_ = __n;
}
}
#endif
Expand All @@ -633,7 +620,8 @@ _LIBCPP_CONSTEXPR_SINCE_CXX20 vector<bool, _Allocator>::vector(size_type __n, co
: __begin_(nullptr), __size_(0), __cap_(0) {
if (__n > 0) {
__vallocate(__n);
__construct_at_end(__n, __x);
std::fill_n(__begin_, __external_cap_to_internal(__n), __storage_type(0) - __x);
__size_ = __n;
}
}

Expand All @@ -643,7 +631,8 @@ vector<bool, _Allocator>::vector(size_type __n, const value_type& __x, const all
: __begin_(nullptr), __size_(0), __cap_(0), __alloc_(static_cast<__storage_allocator>(__a)) {
if (__n > 0) {
__vallocate(__n);
__construct_at_end(__n, __x);
std::fill_n(__begin_, __external_cap_to_internal(__n), __storage_type(0) - __x);
__size_ = __n;
}
}

Expand Down
20 changes: 20 additions & 0 deletions libcxx/test/benchmarks/containers/sequence/vector_bool.bench.cpp
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Original file line number Diff line number Diff line change
@@ -0,0 +1,20 @@
//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

#include <benchmark/benchmark.h>
#include <vector>

static void BM_vector_bool_size_ctor(benchmark::State& state) {
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I assume it doesn't work to use the generic sequence benchmarks since vector<bool> is "special"?

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Yes, exactly. I wanted to use them first, but vector<bool> isn't a sequence container, so the benchmarks don't work properly.

for (auto _ : state) {
std::vector<bool> vec(100, true);
benchmark::DoNotOptimize(vec);
}
}
BENCHMARK(BM_vector_bool_size_ctor);

BENCHMARK_MAIN();
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