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libstdc++: Rearrange some range adaptors' data members

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Since the standard range adaptors are specified to derive from the empty
class view_base, having their first data member store the underlying
view is suboptimal, for if the underlying view also derives from
view_base then the two view_base subobjects will be adjacent; this
prevents the compiler from applying the empty base optimization to elide
away the storage for these two empty bases.

This patch improves the situation by declaring the _M_base data member
last instead of first in each range adaptor that has more than one data
member, so that the empty base optimization can apply in more cases.

libstdc++-v3/ChangeLog:

	* include/std/ranges (filter_view): Declare the data member
	_M_base last instead of first, and adjust constructors' member
	initializer lists accordingly.
	(transform_view): Likewise.
	(take_view): Likewise.
	(take_while_view): Likewise.
	(drop_view): Likewise.
	(drop_while_view): Likewise.
	(join_view): Likewise.
	(split_view): Likewise (and tweak nearby formatting).
	(reverse_view): Likewise.
	* testsuite/std/ranges/adaptors/sizeof.cc: Update expected
	sizes.
This commit is contained in:
Patrick Palka 2020-09-28 12:05:32 -04:00
parent ea51fba504
commit 361e32eeaa
2 changed files with 32 additions and 35 deletions
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47
libstdc++-v3/include/std/ranges
View File

@ -1250,16 +1250,16 @@ namespace views
{ return __y.__equal(__x); }
};
_Vp _M_base = _Vp();
[[no_unique_address]] __detail::__box<_Pred> _M_pred;
[[no_unique_address]] __detail::_CachedPosition<_Vp> _M_cached_begin;
_Vp _M_base = _Vp();
public:
filter_view() = default;
constexpr
filter_view(_Vp __base, _Pred __pred)
: _M_base(std::move(__base)), _M_pred(std::move(__pred))
: _M_pred(std::move(__pred)), _M_base(std::move(__base))
{ }
constexpr _Vp
@ -1588,15 +1588,15 @@ namespace views
friend _Sentinel<!_Const>;
};
_Vp _M_base = _Vp();
[[no_unique_address]] __detail::__box<_Fp> _M_fun;
_Vp _M_base = _Vp();
public:
transform_view() = default;
constexpr
transform_view(_Vp __base, _Fp __fun)
: _M_base(std::move(__base)), _M_fun(std::move(__fun))
: _M_fun(std::move(__fun)), _M_base(std::move(__base))
{ }
constexpr _Vp
@ -1695,15 +1695,15 @@ namespace views
friend _Sentinel<!_Const>;
};
_Vp _M_base = _Vp();
range_difference_t<_Vp> _M_count = 0;
_Vp _M_base = _Vp();
public:
take_view() = default;
constexpr
take_view(_Vp base, range_difference_t<_Vp> __count)
: _M_base(std::move(base)), _M_count(std::move(__count))
: _M_count(std::move(__count)), _M_base(std::move(base))
{ }
constexpr _Vp
@ -1842,17 +1842,16 @@ namespace views
friend _Sentinel<!_Const>;
};
_Vp _M_base = _Vp();
[[no_unique_address]] __detail::__box<_Pred> _M_pred;
_Vp _M_base = _Vp();
public:
take_while_view() = default;
constexpr
take_while_view(_Vp base, _Pred __pred)
: _M_base(std::move(base)), _M_pred(std::move(__pred))
{
}
: _M_pred(std::move(__pred)), _M_base(std::move(base))
{ }
constexpr _Vp
base() const& requires copy_constructible<_Vp>
@ -1902,8 +1901,8 @@ namespace views
class drop_view : public view_interface<drop_view<_Vp>>
{
private:
_Vp _M_base = _Vp();
range_difference_t<_Vp> _M_count = 0;
_Vp _M_base = _Vp();
// ranges::next(begin(base), count, end(base)) is O(1) if _Vp satisfies
// both random_access_range and sized_range. Otherwise, cache its result.
@ -1919,7 +1918,7 @@ namespace views
constexpr
drop_view(_Vp __base, range_difference_t<_Vp> __count)
: _M_base(std::move(__base)), _M_count(__count)
: _M_count(__count), _M_base(std::move(__base))
{ __glibcxx_assert(__count >= 0); }
constexpr _Vp
@ -2002,16 +2001,16 @@ namespace views
class drop_while_view : public view_interface<drop_while_view<_Vp, _Pred>>
{
private:
_Vp _M_base = _Vp();
[[no_unique_address]] __detail::__box<_Pred> _M_pred;
[[no_unique_address]] __detail::_CachedPosition<_Vp> _M_cached_begin;
_Vp _M_base = _Vp();
public:
drop_while_view() = default;
constexpr
drop_while_view(_Vp __base, _Pred __pred)
: _M_base(std::move(__base)), _M_pred(std::move(__pred))
: _M_pred(std::move(__pred)), _M_base(std::move(__base))
{ }
constexpr _Vp
@ -2300,12 +2299,11 @@ namespace views
friend _Sentinel<!_Const>;
};
_Vp _M_base = _Vp();
// XXX: _M_inner is "present only when !is_reference_v<_InnerRange>"
[[no_unique_address]]
__detail::__maybe_present_t<!is_reference_v<_InnerRange>,
views::all_t<_InnerRange>> _M_inner;
_Vp _M_base = _Vp();
public:
join_view() = default;
@ -2680,13 +2678,12 @@ namespace views
{ ranges::iter_swap(__x._M_i_current(), __y._M_i_current()); }
};
_Vp _M_base = _Vp();
_Pattern _M_pattern = _Pattern();
// XXX: _M_current is "present only if !forward_range<V>"
[[no_unique_address]]
__detail::__maybe_present_t<!forward_range<_Vp>, iterator_t<_Vp>>
_M_current;
__detail::__maybe_present_t<!forward_range<_Vp>,
iterator_t<_Vp>> _M_current;
_Vp _M_base = _Vp();
public:
@ -2694,7 +2691,7 @@ namespace views
constexpr
split_view(_Vp __base, _Pattern __pattern)
: _M_base(std::move(__base)), _M_pattern(std::move(__pattern))
: _M_pattern(std::move(__pattern)), _M_base(std::move(__base))
{ }
template<input_range _Range>
@ -2702,8 +2699,8 @@ namespace views
&& constructible_from<_Pattern, single_view<range_value_t<_Range>>>
constexpr
split_view(_Range&& __r, range_value_t<_Range> __e)
: _M_base(views::all(std::forward<_Range>(__r))),
_M_pattern(std::move(__e))
: _M_pattern(std::move(__e)),
_M_base(views::all(std::forward<_Range>(__r)))
{ }
constexpr _Vp
@ -2892,14 +2889,14 @@ namespace views
class reverse_view : public view_interface<reverse_view<_Vp>>
{
private:
_Vp _M_base = _Vp();
static constexpr bool _S_needs_cached_begin
= !common_range<_Vp> && !random_access_range<_Vp>;
[[no_unique_address]]
__detail::__maybe_present_t<_S_needs_cached_begin,
__detail::_CachedPosition<_Vp>>
_M_cached_begin;
_Vp _M_base = _Vp();
public:
reverse_view() = default;

20
libstdc++-v3/testsuite/std/ranges/adaptors/sizeof.cc
View File

@ -33,20 +33,20 @@ using V = ranges::subrange<int*, int*>;
constexpr auto ptr = sizeof(int*);
static_assert(sizeof(V) == 2*ptr);
static_assert(sizeof(ranges::take_view<V>) == 4*ptr);
static_assert(sizeof(ranges::drop_view<V>) == 4*ptr);
static_assert(sizeof(ranges::take_view<V>) == 3*ptr);
static_assert(sizeof(ranges::drop_view<V>) == 3*ptr);
static_assert(sizeof(ranges::filter_view<V, decltype(&pred_f)>) == 5*ptr);
static_assert(sizeof(ranges::take_while_view<V, decltype(&pred_f)>) == 4*ptr);
static_assert(sizeof(ranges::drop_while_view<V, decltype(&pred_f)>) == 5*ptr);
static_assert(sizeof(ranges::transform_view<V, decltype(&func_f)>) == 4*ptr);
static_assert(sizeof(ranges::filter_view<V, decltype(&pred_f)>) == 4*ptr);
static_assert(sizeof(ranges::take_while_view<V, decltype(&pred_f)>) == 3*ptr);
static_assert(sizeof(ranges::drop_while_view<V, decltype(&pred_f)>) == 4*ptr);
static_assert(sizeof(ranges::transform_view<V, decltype(&func_f)>) == 3*ptr);
static_assert(sizeof(ranges::filter_view<V, decltype(pred_l)>) == 4*ptr);
static_assert(sizeof(ranges::filter_view<V, decltype(pred_l)>) == 3*ptr);
static_assert(sizeof(ranges::take_while_view<V, decltype(pred_l)>) == 3*ptr);
static_assert(sizeof(ranges::drop_while_view<V, decltype(pred_l)>) == 4*ptr);
static_assert(sizeof(ranges::drop_while_view<V, decltype(pred_l)>) == 3*ptr);
static_assert(sizeof(ranges::transform_view<V, decltype(func_l)>) == 3*ptr);
static_assert(sizeof(ranges::split_view<V, std::string_view>) == 5*ptr);
static_assert(sizeof(ranges::split_view<V, std::string_view>) == 4*ptr);
static_assert
(sizeof(ranges::reverse_view<ranges::filter_view<V, decltype(pred_l)>>) == 5*ptr);
(sizeof(ranges::reverse_view<ranges::filter_view<V, decltype(pred_l)>>) == 4*ptr);