Tested on x86_64-pc-linux-gnu, does this look OK for trunk?
-- >8 --
Some _Safe_iterator member functions define a variable of non-literal
type __gnu_cxx::__scoped_lock, which automatically disqualifies them from
being constexpr in C++20 mode even if that code path is never constant
evaluated. This restriction was lifted by P2242R3 for C++23, but we
need to work around it in C++20 mode. To that end this patch defines
a pair of macros that encapsulate the lambda-based workaround mentioned
in that paper and uses them to make the functions valid C++20 constexpr
functions. The augmented std::vector test element_access/constexpr.cc
now successfully compiles in C++20 mode with -D_GLIBCXX_DEBUG (and it
tests all modified member functions).
libstdc++-v3/ChangeLog:
* include/debug/safe_base.h (_Safe_sequence_base::_M_swap):
Remove _GLIBCXX20_CONSTEXPR.
* include/debug/safe_iterator.h
(_GLIBCXX20_CONSTEXPR_NON_LITERAL_SCOPE_BEGIN):
(_GLIBCXX20_CONSTEXPR_NON_LITERAL_SCOPE_END): Define.
(_Safe_iterator::operator=): Use them around the code path that
defines a variable of type __gnu_cxx::__scoped_lock.
(_Safe_iterator::operator++): Likewise.
(_Safe_iterator::operator--): Likewise.
(_Safe_iterator::operator+=): Likewise.
(_Safe_iterator::operator-=): Likewise.
* testsuite/23_containers/vector/element_access/constexpr.cc
(test_iterators): Also test copy and move assignment.
* testsuite/std/ranges/adaptors/all.cc (test08) [_GLIBCXX_DEBUG]:
Use std::vector unconditionally.
---
libstdc++-v3/include/debug/safe_base.h | 1 -
libstdc++-v3/include/debug/safe_iterator.h | 48 ++++++++++++++-----
.../vector/element_access/constexpr.cc | 2 +
.../testsuite/std/ranges/adaptors/all.cc | 4 --
4 files changed, 38 insertions(+), 17 deletions(-)
diff --git a/libstdc++-v3/include/debug/safe_base.h
b/libstdc++-v3/include/debug/safe_base.h
index 107fef3cb02..d5fbe4b1320 100644
--- a/libstdc++-v3/include/debug/safe_base.h
+++ b/libstdc++-v3/include/debug/safe_base.h
@@ -268,7 +268,6 @@ namespace __gnu_debug
* operation is complete all iterators that originally referenced
* one container now reference the other container.
*/
- _GLIBCXX20_CONSTEXPR
void
_M_swap(_Safe_sequence_base& __x) _GLIBCXX_USE_NOEXCEPT;
diff --git a/libstdc++-v3/include/debug/safe_iterator.h
b/libstdc++-v3/include/debug/safe_iterator.h
index 1bc7c904ee0..929fd9b0ade 100644
--- a/libstdc++-v3/include/debug/safe_iterator.h
+++ b/libstdc++-v3/include/debug/safe_iterator.h
@@ -65,6 +65,20 @@
_GLIBCXX_DEBUG_VERIFY_OPERANDS(_Lhs, _Rhs, __msg_distance_bad, \
__msg_distance_different)
+// This pair of macros helps with writing valid C++20 constexpr functions that
+// contain a non-constexpr code path that defines a non-literal variable, which
+// was otherwise disallowed until P2242R3 for C++23. We use them below for
+// __gnu_cxx::__scoped_lock so that the containing functions are still
+// considered valid C++20 constexpr functions.
+
+#if __cplusplus >= 202002L && __cpp_constexpr < 202110L
+# define _GLIBCXX20_CONSTEXPR_NON_LITERAL_SCOPE_BEGIN [&]() -> void { do
+# define _GLIBCXX20_CONSTEXPR_NON_LITERAL_SCOPE_END while(false); }();
+#else
+# define _GLIBCXX20_CONSTEXPR_NON_LITERAL_SCOPE_BEGIN
+# define _GLIBCXX20_CONSTEXPR_NON_LITERAL_SCOPE_END
+#endif
+
namespace __gnu_debug
{
/** Helper struct to deal with sequence offering a before_begin
@@ -266,11 +280,11 @@ namespace __gnu_debug
._M_iterator(__x, "other"));
if (this->_M_sequence && this->_M_sequence == __x._M_sequence)
- {
+ _GLIBCXX20_CONSTEXPR_NON_LITERAL_SCOPE_BEGIN {
__gnu_cxx::__scoped_lock __l(this->_M_get_mutex());
base() = __x.base();
_M_version = __x._M_sequence->_M_version;
- }
+ } _GLIBCXX20_CONSTEXPR_NON_LITERAL_SCOPE_END
else
{
_M_detach();
@@ -306,11 +320,11 @@ namespace __gnu_debug
return *this;
if (this->_M_sequence && this->_M_sequence == __x._M_sequence)
- {
+ _GLIBCXX20_CONSTEXPR_NON_LITERAL_SCOPE_BEGIN {
__gnu_cxx::__scoped_lock __l(this->_M_get_mutex());
base() = __x.base();
_M_version = __x._M_sequence->_M_version;
- }
+ } _GLIBCXX20_CONSTEXPR_NON_LITERAL_SCOPE_END
else
{
_M_detach();
@@ -378,8 +392,10 @@ namespace __gnu_debug
_GLIBCXX_DEBUG_VERIFY(this->_M_incrementable(),
_M_message(__msg_bad_inc)
._M_iterator(*this, "this"));
- __gnu_cxx::__scoped_lock __l(this->_M_get_mutex());
- ++base();
+ _GLIBCXX20_CONSTEXPR_NON_LITERAL_SCOPE_BEGIN {
+ __gnu_cxx::__scoped_lock __l(this->_M_get_mutex());
+ ++base();
+ } _GLIBCXX20_CONSTEXPR_NON_LITERAL_SCOPE_END
return *this;
}
@@ -697,8 +713,10 @@ namespace __gnu_debug
_GLIBCXX_DEBUG_VERIFY(this->_M_decrementable(),
_M_message(__msg_bad_dec)
._M_iterator(*this, "this"));
- __gnu_cxx::__scoped_lock __l(this->_M_get_mutex());
- --this->base();
+ _GLIBCXX20_CONSTEXPR_NON_LITERAL_SCOPE_BEGIN {
+ __gnu_cxx::__scoped_lock __l(this->_M_get_mutex());
+ --this->base();
+ } _GLIBCXX20_CONSTEXPR_NON_LITERAL_SCOPE_END
return *this;
}
@@ -912,8 +930,10 @@ namespace __gnu_debug
_GLIBCXX_DEBUG_VERIFY(this->_M_can_advance(__n),
_M_message(__msg_advance_oob)
._M_iterator(*this)._M_integer(__n));
- __gnu_cxx::__scoped_lock __l(this->_M_get_mutex());
- this->base() += __n;
+ _GLIBCXX20_CONSTEXPR_NON_LITERAL_SCOPE_BEGIN {
+ __gnu_cxx::__scoped_lock __l(this->_M_get_mutex());
+ this->base() += __n;
+ } _GLIBCXX20_CONSTEXPR_NON_LITERAL_SCOPE_END
return *this;
}
@@ -930,8 +950,10 @@ namespace __gnu_debug
_GLIBCXX_DEBUG_VERIFY(this->_M_can_advance(-__n),
_M_message(__msg_retreat_oob)
._M_iterator(*this)._M_integer(__n));
- __gnu_cxx::__scoped_lock __l(this->_M_get_mutex());
- this->base() -= __n;
+ _GLIBCXX20_CONSTEXPR_NON_LITERAL_SCOPE_BEGIN {
+ __gnu_cxx::__scoped_lock __l(this->_M_get_mutex());
+ this->base() -= __n;
+ } _GLIBCXX20_CONSTEXPR_NON_LITERAL_SCOPE_END
return *this;
}
@@ -1156,6 +1178,8 @@ _GLIBCXX_END_NAMESPACE_VERSION
}
#endif
+#undef _GLIBCXX20_CONSTEXPR_NON_LITERAL_SCOPE_END
+#undef _GLIBCXX20_CONSTEXPR_NON_LITERAL_SCOPE_BEGIN
#undef _GLIBCXX_DEBUG_VERIFY_DIST_OPERANDS
#undef _GLIBCXX_DEBUG_VERIFY_REL_OPERANDS
#undef _GLIBCXX_DEBUG_VERIFY_EQ_OPERANDS
diff --git
a/libstdc++-v3/testsuite/23_containers/vector/element_access/constexpr.cc
b/libstdc++-v3/testsuite/23_containers/vector/element_access/constexpr.cc
index ee93d2fd95e..ab1e7f1bb70 100644
--- a/libstdc++-v3/testsuite/23_containers/vector/element_access/constexpr.cc
+++ b/libstdc++-v3/testsuite/23_containers/vector/element_access/constexpr.cc
@@ -25,6 +25,8 @@ test_iterators()
it -= 2;
it += 1;
VERIFY( (it + 1) == v.end() );
+ it = it + 1;
+ it = it;
auto rit = v.rbegin();
VERIFY( &*rit == &v.back() );
diff --git a/libstdc++-v3/testsuite/std/ranges/adaptors/all.cc
b/libstdc++-v3/testsuite/std/ranges/adaptors/all.cc
index e7010f80e18..5f7206dc8c3 100644
--- a/libstdc++-v3/testsuite/std/ranges/adaptors/all.cc
+++ b/libstdc++-v3/testsuite/std/ranges/adaptors/all.cc
@@ -156,11 +156,7 @@ test07()
constexpr bool
test08()
{
-#ifdef _GLIBCXX_DEBUG
- using std::_GLIBCXX_STD_C::vector;
-#else
using std::vector;
-#endif
// Verify P2415R2 "What is a view?" changes.
// In particular, rvalue non-view non-borrowed ranges are now viewable.
--
2.43.0.367.g186b115d30
