diff --git a/libcxx/include/vector b/libcxx/include/vector index 299ad8c9b23f28..7c7adb0da7da59 100644 --- a/libcxx/include/vector +++ b/libcxx/include/vector @@ -1443,7 +1443,11 @@ _LIBCPP_CONSTEXPR_SINCE_CXX20 void vector<_Tp, _Allocator>::shrink_to_fit() _NOE #endif // _LIBCPP_HAS_NO_EXCEPTIONS allocator_type& __a = this->__alloc(); __split_buffer __v(size(), size(), __a); - __swap_out_circular_buffer(__v); + // The Standard mandates shrink_to_fit() does not increase the capacity. + // With equal capacity keep the existing buffer. This avoids extra work + // due to swapping the elements. + if (__v.capacity() < capacity()) + __swap_out_circular_buffer(__v); #ifndef _LIBCPP_HAS_NO_EXCEPTIONS } catch (...) { } diff --git a/libcxx/test/std/containers/sequences/vector/vector.capacity/shrink_to_fit.pass.cpp b/libcxx/test/std/containers/sequences/vector/vector.capacity/shrink_to_fit.pass.cpp index 8851e2a9ed0c7c..facb724c713af0 100644 --- a/libcxx/test/std/containers/sequences/vector/vector.capacity/shrink_to_fit.pass.cpp +++ b/libcxx/test/std/containers/sequences/vector/vector.capacity/shrink_to_fit.pass.cpp @@ -71,9 +71,46 @@ TEST_CONSTEXPR_CXX20 bool tests() { return true; } +std::size_t min_bytes = 1000; + +template +struct increasing_allocator { + using value_type = T; + increasing_allocator() = default; + template + increasing_allocator(const increasing_allocator&) noexcept {} + std::allocation_result allocate_at_least(std::size_t n) { + std::size_t allocation_amount = n * sizeof(T); + if (allocation_amount < min_bytes) + allocation_amount = min_bytes; + min_bytes += 1000; + return {static_cast(::operator new(allocation_amount)), allocation_amount}; + } + T* allocate(std::size_t n) { return allocate_at_least(n).ptr; } + void deallocate(T* p, std::size_t) noexcept { ::operator delete(static_cast(p)); } +}; + +template +bool operator==(increasing_allocator, increasing_allocator) { + return true; +} + +// https://github.com/llvm/llvm-project/issues/95161 +void test_increasing_allocator() { + std::vector> v; + v.push_back(1); + assert(is_contiguous_container_asan_correct(v)); + std::size_t capacity = v.capacity(); + v.shrink_to_fit(); + assert(v.capacity() == capacity); + assert(v.size() == 1); + assert(is_contiguous_container_asan_correct(v)); +} + int main(int, char**) { tests(); + test_increasing_allocator(); #if TEST_STD_VER > 17 static_assert(tests()); #endif