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[libc++] default some special members in map and set #147081

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Merged
merged 1 commit into from
Jul 5, 2025
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[libc++] default some special members in map and set #147081

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45 changes: 7 additions & 38 deletions libcxx/include/map
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Original file line number Diff line number Diff line change
Expand Up @@ -972,31 +972,15 @@ public:

_LIBCPP_HIDE_FROM_ABI map(const map& __m) : __tree_(__m.__tree_) { insert(__m.begin(), __m.end()); }

_LIBCPP_HIDE_FROM_ABI map& operator=(const map& __m) {
# ifndef _LIBCPP_CXX03_LANG
__tree_ = __m.__tree_;
# else
if (this != std::addressof(__m)) {
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It's not clear to me that before/after are equivalent in non-C++03 mode -- can you explain why they are?

Also, I had played around this area in https://reviews.llvm.org/D121485 (which never landed), can you take a look and ensure that concerns back then don't apply to this? Finally, can you benchmark before/after? In principle, we shouldn't see a difference IIUC?

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It's not clear to me that before/after are equivalent in non-C++03 mode -- can you explain why they are?

__tree_ is the only member of map, so the compiler-generated code just calls the assignment operator of __tree_.

Also, I had played around this area in https://reviews.llvm.org/D121485 (which never landed), can you take a look and ensure that concerns back then don't apply to this?

I guess Mark's comment in map, line 1902, is relevant here, but I don't think the concern is correct. We're calling __tree::clear() if we assign a new allocator and reuse the old nodes oterwise.

Finally, can you benchmark before/after?

I haven't benchmarked, but I have looked at the code gen before landing the patch, which was identical (even at -O0). Is that good enough?

In principle, we shouldn't see a difference IIUC?

Correct.

__tree_.clear();
__tree_.value_comp() = __m.__tree_.value_comp();
__tree_.__copy_assign_alloc(__m.__tree_);
insert(__m.begin(), __m.end());
}
# endif
return *this;
}
_LIBCPP_HIDE_FROM_ABI map& operator=(const map& __m) = default;

# ifndef _LIBCPP_CXX03_LANG

_LIBCPP_HIDE_FROM_ABI map(map&& __m) noexcept(is_nothrow_move_constructible<__base>::value)
: __tree_(std::move(__m.__tree_)) {}
_LIBCPP_HIDE_FROM_ABI map(map&& __m) noexcept(is_nothrow_move_constructible<__base>::value) = default;

_LIBCPP_HIDE_FROM_ABI map(map&& __m, const allocator_type& __a);

_LIBCPP_HIDE_FROM_ABI map& operator=(map&& __m) noexcept(is_nothrow_move_assignable<__base>::value) {
__tree_ = std::move(__m.__tree_);
return *this;
}
_LIBCPP_HIDE_FROM_ABI map& operator=(map&& __m) noexcept(is_nothrow_move_assignable<__base>::value) = default;

_LIBCPP_HIDE_FROM_ABI map(initializer_list<value_type> __il, const key_compare& __comp = key_compare())
: __tree_(__vc(__comp)) {
Expand Down Expand Up @@ -1659,31 +1643,16 @@ public:
insert(__m.begin(), __m.end());
}

_LIBCPP_HIDE_FROM_ABI multimap& operator=(const multimap& __m) {
# ifndef _LIBCPP_CXX03_LANG
__tree_ = __m.__tree_;
# else
if (this != std::addressof(__m)) {
__tree_.clear();
__tree_.value_comp() = __m.__tree_.value_comp();
__tree_.__copy_assign_alloc(__m.__tree_);
insert(__m.begin(), __m.end());
}
# endif
return *this;
}
_LIBCPP_HIDE_FROM_ABI multimap& operator=(const multimap& __m) = default;

# ifndef _LIBCPP_CXX03_LANG

_LIBCPP_HIDE_FROM_ABI multimap(multimap&& __m) noexcept(is_nothrow_move_constructible<__base>::value)
: __tree_(std::move(__m.__tree_)) {}
_LIBCPP_HIDE_FROM_ABI multimap(multimap&& __m) noexcept(is_nothrow_move_constructible<__base>::value) = default;

_LIBCPP_HIDE_FROM_ABI multimap(multimap&& __m, const allocator_type& __a);

_LIBCPP_HIDE_FROM_ABI multimap& operator=(multimap&& __m) noexcept(is_nothrow_move_assignable<__base>::value) {
__tree_ = std::move(__m.__tree_);
return *this;
}
_LIBCPP_HIDE_FROM_ABI multimap&
operator=(multimap&& __m) noexcept(is_nothrow_move_assignable<__base>::value) = default;

_LIBCPP_HIDE_FROM_ABI multimap(initializer_list<value_type> __il, const key_compare& __comp = key_compare())
: __tree_(__vc(__comp)) {
Expand Down
16 changes: 4 additions & 12 deletions libcxx/include/set
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Original file line number Diff line number Diff line change
Expand Up @@ -662,14 +662,10 @@ public:

_LIBCPP_HIDE_FROM_ABI set(const set& __s) : __tree_(__s.__tree_) { insert(__s.begin(), __s.end()); }

_LIBCPP_HIDE_FROM_ABI set& operator=(const set& __s) {
__tree_ = __s.__tree_;
return *this;
}
_LIBCPP_HIDE_FROM_ABI set& operator=(const set& __s) = default;

# ifndef _LIBCPP_CXX03_LANG
_LIBCPP_HIDE_FROM_ABI set(set&& __s) noexcept(is_nothrow_move_constructible<__base>::value)
: __tree_(std::move(__s.__tree_)) {}
_LIBCPP_HIDE_FROM_ABI set(set&& __s) noexcept(is_nothrow_move_constructible<__base>::value) = default;
# endif // _LIBCPP_CXX03_LANG

_LIBCPP_HIDE_FROM_ABI explicit set(const allocator_type& __a) : __tree_(__a) {}
Expand Down Expand Up @@ -1129,14 +1125,10 @@ public:
insert(__s.begin(), __s.end());
}

_LIBCPP_HIDE_FROM_ABI multiset& operator=(const multiset& __s) {
__tree_ = __s.__tree_;
return *this;
}
_LIBCPP_HIDE_FROM_ABI multiset& operator=(const multiset& __s) = default;

# ifndef _LIBCPP_CXX03_LANG
_LIBCPP_HIDE_FROM_ABI multiset(multiset&& __s) noexcept(is_nothrow_move_constructible<__base>::value)
: __tree_(std::move(__s.__tree_)) {}
_LIBCPP_HIDE_FROM_ABI multiset(multiset&& __s) noexcept(is_nothrow_move_constructible<__base>::value) = default;

_LIBCPP_HIDE_FROM_ABI multiset(multiset&& __s, const allocator_type& __a);
# endif // _LIBCPP_CXX03_LANG
Expand Down
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