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QVLA: Optimize assign() for non-throwing copies

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Change-Id: I39e2bef482fa638a6d197623759b5163fc7cc3a6
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
This commit is contained in:
Mårten Nordheim 2023-02-16 11:23:18 +01:00
parent cb15967014
commit 2457dd8bd0
1 changed files with 17 additions and 6 deletions
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23
src/corelib/tools/qvarlengtharray.h
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@ -779,7 +779,10 @@ template <typename Iterator>
Q_OUTOFLINE_TEMPLATE void QVLABase<T>::assign_impl(qsizetype prealloc, void *array, Iterator first, Iterator last)
{
// This function only provides the basic exception guarantee.
if constexpr (std::is_convertible_v<typename std::iterator_traits<Iterator>::iterator_category, std::forward_iterator_tag>) {
constexpr bool IsFwdIt =
std::is_convertible_v<typename std::iterator_traits<Iterator>::iterator_category,
std::forward_iterator_tag>;
if constexpr (IsFwdIt) {
const qsizetype n = std::distance(first, last);
if (n > capacity())
reallocate_impl(prealloc, array, 0, n); // clear & reserve n
@ -792,11 +795,19 @@ Q_OUTOFLINE_TEMPLATE void QVLABase<T>::assign_impl(qsizetype prealloc, void *arr
++first;
}
qsizetype n = dst - begin();
while (first != last) {
emplace_back_impl(prealloc, array, *first);
++first;
++n;
qsizetype n = 0;
if constexpr (IsFwdIt && noexcept(T(*first))) {
dst = std::uninitialized_copy(first, last, dst);
n = dst - begin();
if (n > s) // otherwise: readjust 's' in erase() later
s = n;
} else {
n = dst - begin();
while (first != last) {
emplace_back_impl(prealloc, array, *first);
++first;
++n;
}
}
erase(data() + n, data() + size());
}