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Fixes #197 ("small_vector::swap causes spurious allocations and suboptimal performance")

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Ion Gaztañaga
2021-11-01 00:19:16 +01:00
parent 7f35ef420e
commit f6a03fd3f2
3 changed files with 79 additions and 43 deletions
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include/boost/container/vector.hpp
+28 -18
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@@ -87,8 +87,8 @@ class vec_iterator
//Defining element_type to make libstdc++'s std::pointer_traits well-formed leads to ambiguity
//due to LWG3446. So we need to specialize std::pointer_traits. See
//https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96416 for details. /Many thanks to Jonathan Wakely
//for explaning the issue.
//https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96416 for details. Many thanks to Jonathan Wakely
//for explaining the issue.
#ifndef BOOST_GNU_STDLIB
//Define element_
typedef typename boost::intrusive::pointer_traits<Pointer>::element_type element_type;
@@ -317,7 +317,8 @@ struct vector_alloc_holder
(void)propagate_allocator; (void)p; (void)to_alloc; (void)from_alloc;
const bool all_storage_propagable = !allocator_traits_type::is_partially_propagable::value ||
!allocator_traits_type::storage_is_unpropagable(from_alloc, p);
return all_storage_propagable && (propagate_allocator || allocator_traits_type::equal(from_alloc, to_alloc));
return all_storage_propagable &&
(propagate_allocator || allocator_traits_type::is_always_equal::value || allocator_traits_type::equal(from_alloc, to_alloc));
}
BOOST_CONTAINER_FORCEINLINE
@@ -2549,31 +2550,40 @@ private:
void priv_swap(Vector &x, dtl::false_type) //version_N
{
const bool propagate_alloc = allocator_traits_type::propagate_on_container_swap::value;
if(are_swap_propagable( this->get_stored_allocator(), this->m_holder.start()
, x.get_stored_allocator(), x.m_holder.start(), propagate_alloc)){
if (BOOST_UNLIKELY(&x == this)){
return;
}
else if(are_swap_propagable( this->get_stored_allocator(), this->m_holder.start()
, x.get_stored_allocator(), x.m_holder.start(), propagate_alloc)){
//Just swap internals
this->m_holder.swap_resources(x.m_holder);
}
else{
if (BOOST_UNLIKELY(&x == this))
return;
//Else swap element by element...
bool const t_smaller = this->size() < x.size();
vector &sml = t_smaller ? *this : x;
vector &big = t_smaller ? x : *this;
size_type const common_elements = sml.size();
for(size_type i = 0; i != common_elements; ++i){
boost::adl_move_swap(sml[i], big[i]);
//For empty containers, maybe storage can be moved from the other (just like in the move constructor)
if(sml.empty() && is_propagable_from(big.get_stored_allocator(), big.data(), sml.get_allocator(), propagate_alloc)){
if(BOOST_LIKELY(0u != sml.capacity()))
sml.m_holder.deallocate(sml.m_holder.m_start, sml.m_holder.m_capacity);
sml.steal_resources(big);
}
else {
//Else swap element by element...
size_type const common_elements = sml.size();
for(size_type i = 0; i != common_elements; ++i){
boost::adl_move_swap(sml[i], big[i]);
}
//... and move-insert the remaining range
sml.insert( sml.cend()
, boost::make_move_iterator(boost::movelib::iterator_to_raw_pointer(big.nth(common_elements)))
, boost::make_move_iterator(boost::movelib::iterator_to_raw_pointer(big.end()))
);
//Destroy remaining elements
big.erase(big.nth(common_elements), big.cend());
}
//... and move-insert the remaining range
sml.insert( sml.cend()
, boost::make_move_iterator(boost::movelib::iterator_to_raw_pointer(big.nth(common_elements)))
, boost::make_move_iterator(boost::movelib::iterator_to_raw_pointer(big.end()))
);
//Destroy remaining elements
big.erase(big.nth(common_elements), big.cend());
}
//And now swap the allocator
dtl::swap_alloc(this->m_holder.alloc(), x.m_holder.alloc(), dtl::bool_<propagate_alloc>());