public inbox for libstdc++-cvs@sourceware.org
help / color / mirror / Atom feed
* [gcc r13-113] libstdc++: Simplify std::array accessors [PR104719]
@ 2022-05-04 15:34 Jonathan Wakely
0 siblings, 0 replies; only message in thread
From: Jonathan Wakely @ 2022-05-04 15:34 UTC (permalink / raw)
To: gcc-cvs, libstdc++-cvs
https://gcc.gnu.org/g:ef8d5ac08b5e60f35c52087d88c0235c8ce6b65b
commit r13-113-gef8d5ac08b5e60f35c52087d88c0235c8ce6b65b
Author: Jonathan Wakely <jwakely@redhat.com>
Date: Fri Mar 25 10:28:28 2022 +0000
libstdc++: Simplify std::array accessors [PR104719]
This removes the __array_traits::_S_ref and __array_traits::_S_ptr
accessors, which only exist to make the special case of std::array<T, 0>
syntactically well-formed.
By changing the empty type used as the std::array<T, 0>::_M_elems data
member to support operator[] and conversion to a pointer, we can write
code using the natural syntax. The indirection through _S_ref and
_S_ptr is removed for the common case, and a function call is only used
for the special case of zero-size arrays.
The invalid member access for zero-sized arrays is changed to use
__builtin_trap() instead of a null dereference. This guarantees a
runtime error if it ever gets called, instead of undefined behaviour
that is likely to get optimized out as unreachable.
libstdc++-v3/ChangeLog:
PR libstdc++/104719
* include/std/array (__array_traits::_S_ref): Remove.
(__array_traits::_S_ptr): Remove.
(__array_traits<T, 0>::_Type): Define operator[] and operator T*
to provide an array-like API.
(array::_AT_Type): Remove public typeef.
(array::operator[], array::at, array::front, array::back): Use
index operator to access _M_elems instead of _S_ref.
(array::data): Use implicit conversion from _M_elems to pointer.
(swap(array&, array&)): Use __enable_if_t helper.
(get<I>): Use index operator to access _M_elems.
* testsuite/23_containers/array/tuple_interface/get_neg.cc:
Adjust dg-error line numbers.
Diff:
---
libstdc++-v3/include/std/array | 80 ++++++++++------------
.../23_containers/array/tuple_interface/get_neg.cc | 6 +-
2 files changed, 38 insertions(+), 48 deletions(-)
diff --git a/libstdc++-v3/include/std/array b/libstdc++-v3/include/std/array
index e45143fb329..d1daffee425 100644
--- a/libstdc++-v3/include/std/array
+++ b/libstdc++-v3/include/std/array
@@ -49,36 +49,31 @@ namespace std _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION
- template<typename _Tp, std::size_t _Nm>
+ template<typename _Tp, size_t _Nm>
struct __array_traits
{
- typedef _Tp _Type[_Nm];
- typedef __is_swappable<_Tp> _Is_swappable;
- typedef __is_nothrow_swappable<_Tp> _Is_nothrow_swappable;
-
- static constexpr _Tp&
- _S_ref(const _Type& __t, std::size_t __n) noexcept
- { return const_cast<_Tp&>(__t[__n]); }
-
- static constexpr _Tp*
- _S_ptr(const _Type& __t) noexcept
- { return const_cast<_Tp*>(__t); }
+ using _Type = _Tp[_Nm];
+ using _Is_swappable = __is_swappable<_Tp>;
+ using _Is_nothrow_swappable = __is_nothrow_swappable<_Tp>;
};
template<typename _Tp>
struct __array_traits<_Tp, 0>
{
- struct _Type { };
- typedef true_type _Is_swappable;
- typedef true_type _Is_nothrow_swappable;
-
- static constexpr _Tp&
- _S_ref(const _Type&, std::size_t) noexcept
- { return *static_cast<_Tp*>(nullptr); }
-
- static constexpr _Tp*
- _S_ptr(const _Type&) noexcept
- { return nullptr; }
+ // Empty type used instead of _Tp[0] for std::array<_Tp, 0>.
+ struct _Type
+ {
+ // Indexing is undefined.
+ __attribute__((__always_inline__,__artificial__,__noreturn__))
+ _Tp& operator[](size_t) const noexcept { __builtin_trap(); }
+
+ // Conversion to a pointer produces a null pointer.
+ __attribute__((__always_inline__,__artificial__))
+ operator _Tp*() const noexcept { return nullptr; }
+ };
+
+ using _Is_swappable = true_type;
+ using _Is_nothrow_swappable = true_type;
};
/**
@@ -111,8 +106,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
typedef std::reverse_iterator<const_iterator> const_reverse_iterator;
// Support for zero-sized arrays mandatory.
- typedef __array_traits<_Tp, _Nm> _AT_Type;
- typename _AT_Type::_Type _M_elems;
+ typename __array_traits<_Tp, _Nm>::_Type _M_elems;
// No explicit construct/copy/destroy for aggregate type.
@@ -123,7 +117,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
_GLIBCXX20_CONSTEXPR void
swap(array& __other)
- noexcept(_AT_Type::_Is_nothrow_swappable::value)
+ noexcept(__array_traits<_Tp, _Nm>::_Is_nothrow_swappable::value)
{ std::swap_ranges(begin(), end(), __other.begin()); }
// Iterators.
@@ -206,7 +200,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
operator[](size_type __n) noexcept
{
__glibcxx_requires_subscript(__n);
- return _AT_Type::_S_ref(_M_elems, __n);
+ return _M_elems[__n];
}
[[__nodiscard__]]
@@ -216,7 +210,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
#if __cplusplus >= 201402L
__glibcxx_requires_subscript(__n);
#endif
- return _AT_Type::_S_ref(_M_elems, __n);
+ return _M_elems[__n];
}
_GLIBCXX17_CONSTEXPR reference
@@ -226,7 +220,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
std::__throw_out_of_range_fmt(__N("array::at: __n (which is %zu) "
">= _Nm (which is %zu)"),
__n, _Nm);
- return _AT_Type::_S_ref(_M_elems, __n);
+ return _M_elems[__n];
}
constexpr const_reference
@@ -234,11 +228,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
{
// Result of conditional expression must be an lvalue so use
// boolean ? lvalue : (throw-expr, lvalue)
- return __n < _Nm ? _AT_Type::_S_ref(_M_elems, __n)
+ return __n < _Nm ? _M_elems[__n]
: (std::__throw_out_of_range_fmt(__N("array::at: __n (which is %zu) "
">= _Nm (which is %zu)"),
__n, _Nm),
- _AT_Type::_S_ref(_M_elems, 0));
+ _M_elems[__n]);
}
[[__nodiscard__]]
@@ -246,7 +240,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
front() noexcept
{
__glibcxx_requires_nonempty();
- return *begin();
+ return _M_elems[0];
}
[[__nodiscard__]]
@@ -256,7 +250,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
#if __cplusplus >= 201402L
__glibcxx_requires_nonempty();
#endif
- return _AT_Type::_S_ref(_M_elems, 0);
+ return _M_elems[0];
}
[[__nodiscard__]]
@@ -264,7 +258,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
back() noexcept
{
__glibcxx_requires_nonempty();
- return _Nm ? *(end() - 1) : *end();
+ return _M_elems[_Nm - 1];
}
[[__nodiscard__]]
@@ -274,19 +268,18 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
#if __cplusplus >= 201402L
__glibcxx_requires_nonempty();
#endif
- return _Nm ? _AT_Type::_S_ref(_M_elems, _Nm - 1)
- : _AT_Type::_S_ref(_M_elems, 0);
+ return _M_elems[_Nm - 1];
}
[[__gnu__::__const__, __nodiscard__]]
_GLIBCXX17_CONSTEXPR pointer
data() noexcept
- { return _AT_Type::_S_ptr(_M_elems); }
+ { return _M_elems; }
[[__nodiscard__]]
_GLIBCXX17_CONSTEXPR const_pointer
data() const noexcept
- { return _AT_Type::_S_ptr(_M_elems); }
+ { return _M_elems; }
};
#if __cpp_deduction_guides >= 201606
@@ -371,9 +364,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
inline
#if __cplusplus > 201402L || !defined(__STRICT_ANSI__) // c++1z or gnu++11
// Constrained free swap overload, see p0185r1
- typename enable_if<
- __array_traits<_Tp, _Nm>::_Is_swappable::value
- >::type
+ __enable_if_t<__array_traits<_Tp, _Nm>::_Is_swappable::value>
#else
void
#endif
@@ -383,8 +374,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
#if __cplusplus > 201402L || !defined(__STRICT_ANSI__) // c++1z or gnu++11
template<typename _Tp, std::size_t _Nm>
- typename enable_if<
- !__array_traits<_Tp, _Nm>::_Is_swappable::value>::type
+ __enable_if_t<!__array_traits<_Tp, _Nm>::_Is_swappable::value>
swap(array<_Tp, _Nm>&, array<_Tp, _Nm>&) = delete;
#endif
@@ -394,7 +384,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
get(array<_Tp, _Nm>& __arr) noexcept
{
static_assert(_Int < _Nm, "array index is within bounds");
- return __array_traits<_Tp, _Nm>::_S_ref(__arr._M_elems, _Int);
+ return __arr._M_elems[_Int];
}
template<std::size_t _Int, typename _Tp, std::size_t _Nm>
@@ -412,7 +402,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
get(const array<_Tp, _Nm>& __arr) noexcept
{
static_assert(_Int < _Nm, "array index is within bounds");
- return __array_traits<_Tp, _Nm>::_S_ref(__arr._M_elems, _Int);
+ return __arr._M_elems[_Int];
}
template<std::size_t _Int, typename _Tp, std::size_t _Nm>
diff --git a/libstdc++-v3/testsuite/23_containers/array/tuple_interface/get_neg.cc b/libstdc++-v3/testsuite/23_containers/array/tuple_interface/get_neg.cc
index ea1fd9f2f96..b97149474c9 100644
--- a/libstdc++-v3/testsuite/23_containers/array/tuple_interface/get_neg.cc
+++ b/libstdc++-v3/testsuite/23_containers/array/tuple_interface/get_neg.cc
@@ -26,6 +26,6 @@ int n1 = std::get<1>(a);
int n2 = std::get<1>(std::move(a));
int n3 = std::get<1>(ca);
-// { dg-error "static assertion failed" "" { target *-*-* } 396 }
-// { dg-error "static assertion failed" "" { target *-*-* } 405 }
-// { dg-error "static assertion failed" "" { target *-*-* } 414 }
+// { dg-error "static assertion failed" "" { target *-*-* } 386 }
+// { dg-error "static assertion failed" "" { target *-*-* } 395 }
+// { dg-error "static assertion failed" "" { target *-*-* } 404 }
^ permalink raw reply [flat|nested] only message in thread
only message in thread, other threads:[~2022-05-04 15:34 UTC | newest]
Thread overview: (only message) (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2022-05-04 15:34 [gcc r13-113] libstdc++: Simplify std::array accessors [PR104719] Jonathan Wakely
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).