[PATCH] 77864 Fix noexcept conditions for map/set default constructors
François Dumont
frs.dumont@gmail.com
Tue Oct 25 19:55:00 GMT 2016
On 24/10/2016 13:03, Jonathan Wakely wrote:
> On 12/10/16 22:36 +0200, François Dumont wrote:
>> On 10/10/2016 23:01, Tim Song wrote:
>>> Trying again...with a few edits.
>>>
>>>> On Mon, Oct 10, 2016 at 3:24 PM, François Dumont
>>>> <frs.dumont@gmail.com>
>>>> wrote:
>>>>
>>>> @@ -602,24 +612,32 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>>>> struct _Rb_tree_impl : public _Node_allocator
>>>> {
>>>> _Key_compare _M_key_compare;
>>>> - _Rb_tree_node_base _M_header;
>>>> + _Rb_header_node _M_header;
>>>> +#if __cplusplus < 201103L
>>>> size_type _M_node_count; // Keeps track of size of tree.
>>>> +#else
>>>> + size_type _M_node_count = 0; // Keeps track of size of tree.
>>>> +#endif
>>>>
>>>> +#if __cplusplus < 201103L
>>>> _Rb_tree_impl()
>>>> - : _Node_allocator(), _M_key_compare(), _M_header(),
>>>> - _M_node_count(0)
>>>> - { _M_initialize(); }
>>>> + : _M_node_count(0)
>>>> + { }
>>>> +#else
>>>> + _Rb_tree_impl() = default;
>>>> +#endif
>>>
>>> The default constructor of the associative containers is required to
>>> value-initialize the comparator (see their synopses in
>>> [map/set/multimap/multiset.overview]).
>> I don't have latest Standard version so can't see the exact word but
>> I find quite annoying that the Standard doesn't allow this simple
>> implementation.
>>
>> I don't know if unodered containers have same kind of requirements
>> for equal or hash functors but if so current implementation doesn't
>> do this value initialization.
>>
>> So here is another attempt. This time it simply allows to have
>> noexcept condition in one place and closer to where operations are
>> being invoked.
>>
>> Ok to commit after tests ?
>>
>> François
>>>
>>> _Rb_tree_impl() = default; doesn't do that; it default-initializes the
>>> comparator instead.
>>>
>>> Tim
>>>
>>
>
>> diff --git a/libstdc++-v3/include/bits/stl_map.h
>> b/libstdc++-v3/include/bits/stl_map.h
>> index e5b2a1b..dea7d5b 100644
>> --- a/libstdc++-v3/include/bits/stl_map.h
>> +++ b/libstdc++-v3/include/bits/stl_map.h
>> @@ -167,11 +167,11 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
>> /**
>> * @brief Default constructor creates no elements.
>> */
>> - map()
>> - _GLIBCXX_NOEXCEPT_IF(
>> - is_nothrow_default_constructible<allocator_type>::value
>> - && is_nothrow_default_constructible<key_compare>::value)
>> - : _M_t() { }
>> +#if __cplusplus < 201103L
>> + map() : _M_t() { }
>> +#else
>> + map() = default;
>> +#endif
>>
>> /**
>> * @brief Creates a %map with no elements.
>> diff --git a/libstdc++-v3/include/bits/stl_multimap.h
>> b/libstdc++-v3/include/bits/stl_multimap.h
>> index d240427..7e86b76 100644
>> --- a/libstdc++-v3/include/bits/stl_multimap.h
>> +++ b/libstdc++-v3/include/bits/stl_multimap.h
>> @@ -164,11 +164,11 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
>> /**
>> * @brief Default constructor creates no elements.
>> */
>> - multimap()
>> - _GLIBCXX_NOEXCEPT_IF(
>> - is_nothrow_default_constructible<allocator_type>::value
>> - && is_nothrow_default_constructible<key_compare>::value)
>> - : _M_t() { }
>> +#if __cplusplus < 201103L
>> + multimap() : _M_t() { }
>> +#else
>> + multimap() = default;
>> +#endif
>>
>> /**
>> * @brief Creates a %multimap with no elements.
>> diff --git a/libstdc++-v3/include/bits/stl_multiset.h
>> b/libstdc++-v3/include/bits/stl_multiset.h
>> index cc068a9..7fe2fbd 100644
>> --- a/libstdc++-v3/include/bits/stl_multiset.h
>> +++ b/libstdc++-v3/include/bits/stl_multiset.h
>> @@ -144,11 +144,11 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
>> /**
>> * @brief Default constructor creates no elements.
>> */
>> - multiset()
>> - _GLIBCXX_NOEXCEPT_IF(
>> - is_nothrow_default_constructible<allocator_type>::value
>> - && is_nothrow_default_constructible<key_compare>::value)
>> - : _M_t() { }
>> +#if __cplusplus < 201103L
>> + multiset() : _M_t() { }
>> +#else
>> + multiset() = default;
>> +#endif
>>
>> /**
>> * @brief Creates a %multiset with no elements.
>> diff --git a/libstdc++-v3/include/bits/stl_set.h
>> b/libstdc++-v3/include/bits/stl_set.h
>> index 3938351..5ed9672 100644
>> --- a/libstdc++-v3/include/bits/stl_set.h
>> +++ b/libstdc++-v3/include/bits/stl_set.h
>> @@ -147,11 +147,11 @@ _GLIBCXX_BEGIN_NAMESPACE_CONTAINER
>> /**
>> * @brief Default constructor creates no elements.
>> */
>> - set()
>> - _GLIBCXX_NOEXCEPT_IF(
>> - is_nothrow_default_constructible<allocator_type>::value
>> - && is_nothrow_default_constructible<key_compare>::value)
>> - : _M_t() { }
>> +#if __cplusplus < 201103L
>> + set() : _M_t() { }
>> +#else
>> + set() = default;
>> +#endif
>>
>> /**
>> * @brief Creates a %set with no elements.
>> diff --git a/libstdc++-v3/include/bits/stl_tree.h
>> b/libstdc++-v3/include/bits/stl_tree.h
>> index ee2dc70..b6a3c1e 100644
>> --- a/libstdc++-v3/include/bits/stl_tree.h
>> +++ b/libstdc++-v3/include/bits/stl_tree.h
>> @@ -137,6 +137,16 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>> }
>> };
>>
>> + struct _Rb_header_node : public _Rb_tree_node_base
>> + {
>> + _Rb_header_node() _GLIBCXX_NOEXCEPT
>> + {
>> + _M_color = _S_red;
>> + _M_parent = _Base_ptr();
>> + _M_left = _M_right = this;
>> + }
>> + };
>> +
>> template<typename _Val>
>> struct _Rb_tree_node : public _Rb_tree_node_base
>> {
>> @@ -602,24 +612,34 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>> struct _Rb_tree_impl : public _Node_allocator
>> {
>> _Key_compare _M_key_compare;
>> - _Rb_tree_node_base _M_header;
>> + _Rb_header_node _M_header;
>> +#if __cplusplus < 201103L
>> size_type _M_node_count; // Keeps track of size of tree.
>> +#else
>> + size_type _M_node_count = 0; // Keeps track of size of
>> tree.
>> +#endif
>>
>> _Rb_tree_impl()
>> - : _Node_allocator(), _M_key_compare(), _M_header(),
>> - _M_node_count(0)
>> - { _M_initialize(); }
>> + _GLIBCXX_NOEXCEPT_IF(
>> + is_nothrow_default_constructible<_Node_allocator>::value
>> + && is_nothrow_default_constructible<_Key_compare>::value)
>> + : _M_key_compare()
>> +#if __cplusplus < 201103L
>> + , _M_node_count(0)
>> +#endif
>> + { }
>
> I still think this part is pointless. Why use conditional compilation
> here, when we could just always set it to zero?
>
> What is the advantage of using #if here, except adding more lines of
> code?
>
>>
>> _Rb_tree_impl(const _Key_compare& __comp, const
>> _Node_allocator& __a)
>> - : _Node_allocator(__a), _M_key_compare(__comp), _M_header(),
>> - _M_node_count(0)
>> - { _M_initialize(); }
>> + : _Node_allocator(__a), _M_key_compare(__comp)
>> +#if __cplusplus < 201103L
>> + , _M_node_count(0)
>> +#endif
>> + { }
>>
>> #if __cplusplus >= 201103L
>> _Rb_tree_impl(const _Key_compare& __comp, _Node_allocator&& __a)
>> - : _Node_allocator(std::move(__a)), _M_key_compare(__comp),
>> - _M_header(), _M_node_count(0)
>> - { _M_initialize(); }
>> + : _Node_allocator(std::move(__a)), _M_key_compare(__comp)
>> + { }
>> #endif
>>
>> void
>> @@ -630,16 +650,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>> this->_M_header._M_right = &this->_M_header;
>> this->_M_node_count = 0;
>> }
>> -
>> - private:
>> - void
>> - _M_initialize()
>> - {
>> - this->_M_header._M_color = _S_red;
>> - this->_M_header._M_parent = 0;
>> - this->_M_header._M_left = &this->_M_header;
>> - this->_M_header._M_right = &this->_M_header;
>> - } };
>
> Since we can't remove the constructors that called _M_initialize() we
> don't need to get rid of _M_initialize() either. That means we don't
> need the _Rb_header_node type (so don't need to produce RTTI for a new
> type).
>
> The purpose of the patch is to allow _Rb_tree() = default and then
> set() = default, map() = default etc.
>
> That can be done by simply putting the _GLIBCXX_NOEXCEPT_IF on
> _Rb_tree_impl() and forgetting all the other changes to _Rb_tree_impl.
> Using a default member initializer for _M_node_count and removing
> _M_initialize() aren't necessary to achieve the purpose of the patch
Indeed, here is the simplified patch.
But I will come back to this base type for the next patch to generalize
the defaulted constructors and assignment operators.
Tested under Linux x86_64, ok to commit ?
François
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