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* [gcc r14-8252] libstdc++/debug: Fix constexpr _Safe_iterator in C++20 mode [PR109536]
@ 2024-01-18 15:36 Patrick Palka
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From: Patrick Palka @ 2024-01-18 15:36 UTC (permalink / raw)
To: gcc-cvs, libstdc++-cvs
https://gcc.gnu.org/g:3d3145e9e1461e92bef02d55d36990261dd0444d
commit r14-8252-g3d3145e9e1461e92bef02d55d36990261dd0444d
Author: Patrick Palka <ppalka@redhat.com>
Date: Thu Jan 18 10:36:07 2024 -0500
libstdc++/debug: Fix constexpr _Safe_iterator in C++20 mode [PR109536]
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 it to make these 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
should test all member functions modified by this patch).
PR libstdc++/109536
libstdc++-v3/ChangeLog:
* include/debug/safe_base.h (_Safe_sequence_base::_M_swap):
Remove _GLIBCXX20_CONSTEXPR from non-inline member function.
* include/debug/safe_iterator.h
(_GLIBCXX20_CONSTEXPR_NON_LITERAL_SCOPE_BEGIN): Define.
(_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): Test more iterator operations.
* testsuite/23_containers/vector/bool/element_access/constexpr.cc
(test_iterators): Likewise.
* testsuite/std/ranges/adaptors/all.cc (test08) [_GLIBCXX_DEBUG]:
Remove.
Reviewed-by: Jonathan Wakely <jwakely@redhat.com>
Diff:
---
libstdc++-v3/include/debug/safe_base.h | 1 -
libstdc++-v3/include/debug/safe_iterator.h | 48 ++++++++++++++++------
.../vector/bool/element_access/constexpr.cc | 18 ++++++++
.../vector/element_access/constexpr.cc | 18 ++++++++
libstdc++-v3/testsuite/std/ranges/adaptors/all.cc | 4 --
5 files changed, 72 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..d3e959b8fa7 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 around
+// __gnu_cxx::__scoped_lock variables 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
+# define _GLIBCXX20_CONSTEXPR_NON_LITERAL_SCOPE_END ();
+#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/bool/element_access/constexpr.cc b/libstdc++-v3/testsuite/23_containers/vector/bool/element_access/constexpr.cc
index d6b657e0161..bff9f7b4e0f 100644
--- a/libstdc++-v3/testsuite/23_containers/vector/bool/element_access/constexpr.cc
+++ b/libstdc++-v3/testsuite/23_containers/vector/bool/element_access/constexpr.cc
@@ -18,22 +18,40 @@ test_iterators()
VERIFY( v.crend() == v.rend() );
auto it = v.begin();
+ VERIFY( it[0] == 0 );
VERIFY( *it == v.front() );
+ VERIFY( it[1] == v[1] );
VERIFY( it++ == v.begin() );
VERIFY( ++it == v.end() );
VERIFY( (it - 2) == v.begin() );
+ VERIFY( (it - v.begin()) == 2 );
it -= 2;
it += 1;
VERIFY( (it + 1) == v.end() );
+ VERIFY( (1 + it) == v.end() );
+ it = it + 1;
+ auto it2 = v.begin();
+ std::swap(it, it2);
+ VERIFY( it == v.begin() );
+ VERIFY( it2 == v.end() );
auto rit = v.rbegin();
+ VERIFY( rit[0] == 0 );
VERIFY( *rit == v.back() );
+ VERIFY( rit[1] == v[0] );
VERIFY( rit++ == v.rbegin() );
VERIFY( ++rit == v.rend() );
VERIFY( (rit - 2) == v.rbegin() );
+ VERIFY( (rit - v.rbegin()) == 2 );
rit -= 2;
rit += 1;
VERIFY( (rit + 1) == v.rend() );
+ VERIFY( (1 + rit) == v.rend() );
+ rit = rit + 1;
+ auto rit2 = v.rbegin();
+ std::swap(rit, rit2);
+ VERIFY( rit == v.rbegin() );
+ VERIFY( rit2 == v.rend() );
return true;
}
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..19c91d28cd6 100644
--- a/libstdc++-v3/testsuite/23_containers/vector/element_access/constexpr.cc
+++ b/libstdc++-v3/testsuite/23_containers/vector/element_access/constexpr.cc
@@ -18,22 +18,40 @@ test_iterators()
VERIFY( v.crend() == v.rend() );
auto it = v.begin();
+ VERIFY( it[0] == 0 );
VERIFY( &*it == &v.front() );
+ VERIFY( &it[1] == &v[1] );
VERIFY( it++ == v.begin() );
VERIFY( ++it == v.end() );
VERIFY( (it - 2) == v.begin() );
+ VERIFY( (it - v.begin()) == 2 );
it -= 2;
it += 1;
VERIFY( (it + 1) == v.end() );
+ VERIFY( (1 + it) == v.end() );
+ it = it + 1;
+ auto it2 = v.begin();
+ std::swap(it, it2);
+ VERIFY( it == v.begin() );
+ VERIFY( it2 == v.end() );
auto rit = v.rbegin();
+ VERIFY( rit[0] == 0 );
VERIFY( &*rit == &v.back() );
+ VERIFY( &rit[1] == &v[0] );
VERIFY( rit++ == v.rbegin() );
VERIFY( ++rit == v.rend() );
VERIFY( (rit - 2) == v.rbegin() );
+ VERIFY( (rit - v.rbegin()) == 2 );
rit -= 2;
rit += 1;
VERIFY( (rit + 1) == v.rend() );
+ VERIFY( (1 + rit) == v.rend() );
+ rit = rit + 1;
+ auto rit2 = v.rbegin();
+ std::swap(rit, rit2);
+ VERIFY( rit == v.rbegin() );
+ VERIFY( rit2 == v.rend() );
return true;
}
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.
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