Re: [PATCH] libstdc++: Make __gnu_debug::vector usable in constant expressions [PR109536]
On Sat, 16 Dec 2023 at 16:26, Patrick Palka wrote:
>
> On Sat, 16 Dec 2023, Jonathan Wakely wrote:
>
> > On Sat, 16 Dec 2023 at 09:14, Jonathan Wakely wrote:
> > >
> > > On Sat, 16 Dec 2023 at 00:27, Patrick Palka wrote:
> > > >
> > > > On Wed, 6 Dec 2023, Jonathan Wakely wrote:
> > > >
> > > > > Any comments on this approach?
> > > > >
> > > > > -- >8 --
> > > > >
> > > > > This makes constexpr std::vector (mostly) work in Debug Mode. All safe
> > > > > iterator instrumentation and checking is disabled during constant
> > > > > evaluation, because it requires mutex locks and calls to non-inline
> > > > > functions defined in libstdc++.so. It should be OK to disable the
> > > > > safety
> > > > > checks, because most UB should be detected during constant evaluation
> > > > > anyway.
> > > > >
> > > > > We could try to enable the full checking in constexpr, but it would
> > > > > mean
> > > > > wrapping all the non-inline functions like _M_attach with an inline
> > > > > _M_constexpr_attach that does the iterator housekeeping inline without
> > > > > mutex locks when calling for constant evaluation, and calls the
> > > > > non-inline function at runtime. That could be done in future if we
> > > > > find
> > > > > that we've lost safety or useful checking by disabling the safe
> > > > > iterators.
> > > > >
> > > > > There are a few test failures in C++20 mode, which I'm unable to
> > > > > explain. The _Safe_iterator::operator++() member gives errors for
> > > > > using
> > > > > non-constexpr functions during constant evaluation, even though those
> > > > > functions are guarded by std::is_constant_evaluated() checks. The same
> > > > > code works fine for C++23 and up.
> > > >
> > > > AFAICT these C++20 test failures are really due to the variable
> > > > definition of non-literal type
> > > >
> > > > 381__gnu_cxx::__scoped_lock __l(this->_M_get_mutex());
> > > >
> > > > which were prohibited in a constexpr function (even if that code was
> > > > never executed) until C++23's P2242R3.
> > >
> > > Ah, I figured it was a core change but I couldn't recall which one.
> > > Thanks.
>
> Yeah the diagnostic blaming the non-constexpr call to _M_incrementable
> was outright wrong and misleading, I filed PR113041 about that.
>
> > >
> > > > We can use an immediately invoked lambda to work around this:
> > > >
> > > > 381[this] {
> > > > 382 __gnu_cxx::__scoped_lock __l(this->_M_get_mutex());
> > > > 383 ++base();
> > > > 384}();
> > > > 385return *this;
> > >
> > > We'd need some #if as this code has to work for C++98. But that's doable.
> >
> > The attached patch seems simpler, I'm testing it now.
>
> Would the operator+=, operator-= and the copy assign operator= also need
> adjustment?
Maybe ... which suggest we have missing tests for constexpr vector
(which is probably the case).
>
> We could somewhat cleanly encapsulate the lambda workaround with a pair
> of macros surrounding the problematic variable, something like:
>
> diff --git a/libstdc++-v3/include/debug/safe_iterator.h
> b/libstdc++-v3/include/debug/safe_iterator.h
> index 26f008982f8..df3b4d33f04 100644
> --- a/libstdc++-v3/include/debug/safe_iterator.h
> +++ b/libstdc++-v3/include/debug/safe_iterator.h
> @@ -360,6 +360,14 @@ namespace __gnu_debug
> return base().operator->();
>}
>
> +#if __cplusplus >= 202002L && __cpp_constexpr < 202110L
> +# define _GLIBCXX20_CONSTEXPR_NON_LITERAL_SCOPE_BEGIN [&] { do
> +# define _GLIBCXX20_CONSTEXPR_NON_LITERAL_SCOPE_END while(false); }()
> +#else
> +# define _GLIBCXX20_CONSTEXPR_NON_LITERAL_SCOPE_BEGIN do
> +# define _GLIBCXX20_CONSTEXPR_NON_LITERAL_SCOPE_END while(false)
I think for the limited uses in this file, we don't even need the
do-while, as the code we're enclosing is not a single statement
anyway.
> +#endif
> +
>// -- Input iterator requirements --
>/**
> * @brief Iterator preincrement
> @@ -378,8 +386,10 @@ 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;
>}
>
Yeah, I'll check if other operators need it, and if it's more than
just the two places in my patch I'll go with that.
If I don't get around to it (as I'm meant to have stopped work for the
year yesterday) then feel free to do that.
Re: [PATCH] libstdc++: Make __gnu_debug::vector usable in constant expressions [PR109536]
On Sat, 16 Dec 2023, Jonathan Wakely wrote:
> On Sat, 16 Dec 2023 at 09:14, Jonathan Wakely wrote:
> >
> > On Sat, 16 Dec 2023 at 00:27, Patrick Palka wrote:
> > >
> > > On Wed, 6 Dec 2023, Jonathan Wakely wrote:
> > >
> > > > Any comments on this approach?
> > > >
> > > > -- >8 --
> > > >
> > > > This makes constexpr std::vector (mostly) work in Debug Mode. All safe
> > > > iterator instrumentation and checking is disabled during constant
> > > > evaluation, because it requires mutex locks and calls to non-inline
> > > > functions defined in libstdc++.so. It should be OK to disable the safety
> > > > checks, because most UB should be detected during constant evaluation
> > > > anyway.
> > > >
> > > > We could try to enable the full checking in constexpr, but it would mean
> > > > wrapping all the non-inline functions like _M_attach with an inline
> > > > _M_constexpr_attach that does the iterator housekeeping inline without
> > > > mutex locks when calling for constant evaluation, and calls the
> > > > non-inline function at runtime. That could be done in future if we find
> > > > that we've lost safety or useful checking by disabling the safe
> > > > iterators.
> > > >
> > > > There are a few test failures in C++20 mode, which I'm unable to
> > > > explain. The _Safe_iterator::operator++() member gives errors for using
> > > > non-constexpr functions during constant evaluation, even though those
> > > > functions are guarded by std::is_constant_evaluated() checks. The same
> > > > code works fine for C++23 and up.
> > >
> > > AFAICT these C++20 test failures are really due to the variable
> > > definition of non-literal type
> > >
> > > 381__gnu_cxx::__scoped_lock __l(this->_M_get_mutex());
> > >
> > > which were prohibited in a constexpr function (even if that code was
> > > never executed) until C++23's P2242R3.
> >
> > Ah, I figured it was a core change but I couldn't recall which one. Thanks.
Yeah the diagnostic blaming the non-constexpr call to _M_incrementable
was outright wrong and misleading, I filed PR113041 about that.
> >
> > > We can use an immediately invoked lambda to work around this:
> > >
> > > 381[this] {
> > > 382 __gnu_cxx::__scoped_lock __l(this->_M_get_mutex());
> > > 383 ++base();
> > > 384}();
> > > 385return *this;
> >
> > We'd need some #if as this code has to work for C++98. But that's doable.
>
> The attached patch seems simpler, I'm testing it now.
Would the operator+=, operator-= and the copy assign operator= also need
adjustment?
We could somewhat cleanly encapsulate the lambda workaround with a pair
of macros surrounding the problematic variable, something like:
diff --git a/libstdc++-v3/include/debug/safe_iterator.h
b/libstdc++-v3/include/debug/safe_iterator.h
index 26f008982f8..df3b4d33f04 100644
--- a/libstdc++-v3/include/debug/safe_iterator.h
+++ b/libstdc++-v3/include/debug/safe_iterator.h
@@ -360,6 +360,14 @@ namespace __gnu_debug
return base().operator->();
}
+#if __cplusplus >= 202002L && __cpp_constexpr < 202110L
+# define _GLIBCXX20_CONSTEXPR_NON_LITERAL_SCOPE_BEGIN [&] { do
+# define _GLIBCXX20_CONSTEXPR_NON_LITERAL_SCOPE_END while(false); }()
+#else
+# define _GLIBCXX20_CONSTEXPR_NON_LITERAL_SCOPE_BEGIN do
+# define _GLIBCXX20_CONSTEXPR_NON_LITERAL_SCOPE_END while(false)
+#endif
+
// -- Input iterator requirements --
/**
* @brief Iterator preincrement
@@ -378,8 +386,10 @@ 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;
}
Re: [PATCH] libstdc++: Make __gnu_debug::vector usable in constant expressions [PR109536]
On Sat, 16 Dec 2023 at 09:14, Jonathan Wakely wrote:
>
> On Sat, 16 Dec 2023 at 00:27, Patrick Palka wrote:
> >
> > On Wed, 6 Dec 2023, Jonathan Wakely wrote:
> >
> > > Any comments on this approach?
> > >
> > > -- >8 --
> > >
> > > This makes constexpr std::vector (mostly) work in Debug Mode. All safe
> > > iterator instrumentation and checking is disabled during constant
> > > evaluation, because it requires mutex locks and calls to non-inline
> > > functions defined in libstdc++.so. It should be OK to disable the safety
> > > checks, because most UB should be detected during constant evaluation
> > > anyway.
> > >
> > > We could try to enable the full checking in constexpr, but it would mean
> > > wrapping all the non-inline functions like _M_attach with an inline
> > > _M_constexpr_attach that does the iterator housekeeping inline without
> > > mutex locks when calling for constant evaluation, and calls the
> > > non-inline function at runtime. That could be done in future if we find
> > > that we've lost safety or useful checking by disabling the safe
> > > iterators.
> > >
> > > There are a few test failures in C++20 mode, which I'm unable to
> > > explain. The _Safe_iterator::operator++() member gives errors for using
> > > non-constexpr functions during constant evaluation, even though those
> > > functions are guarded by std::is_constant_evaluated() checks. The same
> > > code works fine for C++23 and up.
> >
> > AFAICT these C++20 test failures are really due to the variable
> > definition of non-literal type
> >
> > 381__gnu_cxx::__scoped_lock __l(this->_M_get_mutex());
> >
> > which were prohibited in a constexpr function (even if that code was
> > never executed) until C++23's P2242R3.
>
> Ah, I figured it was a core change but I couldn't recall which one. Thanks.
>
> > We can use an immediately invoked lambda to work around this:
> >
> > 381[this] {
> > 382 __gnu_cxx::__scoped_lock __l(this->_M_get_mutex());
> > 383 ++base();
> > 384}();
> > 385return *this;
>
> We'd need some #if as this code has to work for C++98. But that's doable.
The attached patch seems simpler, I'm testing it now.
commit 5d70c6c2965647077749a869e9cdbf7e91dba4c7
Author: Jonathan Wakely
Date: Sat Dec 16 09:31:40 2023
libstdc++: Fix errors for constexpr __gnu_debug::vector in C++23 [PR109536]
In the commit log for r14-6553-g7d00a59229ee17 I noted some tests FAIL
in C++20 mode. Patrick identified that they were due to the variable
definitions of non-literal type __scoped_lock, which were prohibited in
a constexpr function (even if that code was never executed) until
C++23's P2242R3.
We can move the problematic code into new non-constexpr functions that
are not called during constant evaluation.
There's also a warning about a constexpr _M_swap function which is never
defined. That's simply because I added the _GLIBCXX20_CONSTEXPR macro on
a member that doesn't need it.
libstdc++-v3/ChangeLog:
PR libstdc++/109536
* include/debug/safe_base.h (_Safe_sequence_base::_M_swap):
Remove _GLIBCXX20_CONSTEXPR from non-inline member function.
* include/debug/safe_iterator.h (_Safe_iterator::_M_move_assign)
diff --git a/libstdc++-v3/include/debug/safe_base.h
b/libstdc++-v3/include/debug/safe_base.h
index d9c17b52b48..1519ad809a4 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 26f008982f8..bde34e1f99c 100644
--- a/libstdc++-v3/include/debug/safe_iterator.h
+++ b/libstdc++-v3/include/debug/safe_iterator.h
@@ -295,7 +295,13 @@ namespace __gnu_debug
base() = __x.base();
return *this;
}
+ _M_move_assign(std::move(__x));
+ return *this;
+ }
+ void
+ _M_move_assign(_Safe_iterator&& __x) noexcept
+ {
_GLIBCXX_DEBUG_VERIFY(!__x._M_singular()
|| __x._M_value_initialized(),
_M_message(__msg_copy_singular)
@@ -303,7 +309,7 @@ namespace __gnu_debug
._M_iterator(__x, "other"));
if (std::__addressof(__x) == this)
- return *this;
+ return;
if (this->_M_sequence && this->_M_sequence == __x._M_sequence)
{
@@ -320,7 +326,6 @@ namespace __gnu_debug
__x._M_detach();
__x.base() = _Iterator();
- return *this;
}
#endif
@@ -370,17 +375,20 @@ namespace __gnu_debug
operator++() _GLIBCXX_NOEXCEPT
{
if
Re: [PATCH] libstdc++: Make __gnu_debug::vector usable in constant expressions [PR109536]
On Sat, 16 Dec 2023 at 00:27, Patrick Palka wrote:
>
> On Wed, 6 Dec 2023, Jonathan Wakely wrote:
>
> > Any comments on this approach?
> >
> > -- >8 --
> >
> > This makes constexpr std::vector (mostly) work in Debug Mode. All safe
> > iterator instrumentation and checking is disabled during constant
> > evaluation, because it requires mutex locks and calls to non-inline
> > functions defined in libstdc++.so. It should be OK to disable the safety
> > checks, because most UB should be detected during constant evaluation
> > anyway.
> >
> > We could try to enable the full checking in constexpr, but it would mean
> > wrapping all the non-inline functions like _M_attach with an inline
> > _M_constexpr_attach that does the iterator housekeeping inline without
> > mutex locks when calling for constant evaluation, and calls the
> > non-inline function at runtime. That could be done in future if we find
> > that we've lost safety or useful checking by disabling the safe
> > iterators.
> >
> > There are a few test failures in C++20 mode, which I'm unable to
> > explain. The _Safe_iterator::operator++() member gives errors for using
> > non-constexpr functions during constant evaluation, even though those
> > functions are guarded by std::is_constant_evaluated() checks. The same
> > code works fine for C++23 and up.
>
> AFAICT these C++20 test failures are really due to the variable
> definition of non-literal type
>
> 381__gnu_cxx::__scoped_lock __l(this->_M_get_mutex());
>
> which were prohibited in a constexpr function (even if that code was
> never executed) until C++23's P2242R3.
Ah, I figured it was a core change but I couldn't recall which one. Thanks.
> We can use an immediately invoked lambda to work around this:
>
> 381[this] {
> 382 __gnu_cxx::__scoped_lock __l(this->_M_get_mutex());
> 383 ++base();
> 384}();
> 385return *this;
We'd need some #if as this code has to work for C++98. But that's doable.
> >
> > libstdc++-v3/ChangeLog:
> >
> > PR libstdc++/109536
> > * include/bits/c++config (__glibcxx_constexpr_assert): Remove
> > macro.
> > * include/bits/stl_algobase.h (__niter_base, __copy_move_a)
> > (__copy_move_backward_a, __fill_a, __fill_n_a, __equal_aux)
> > (__lexicographical_compare_aux): Add constexpr to overloads for
> > debug mode iterators.
> > * include/debug/helper_functions.h (__unsafe): Add constexpr.
> > * include/debug/macros.h (_GLIBCXX_DEBUG_VERIFY_COND_AT): Remove
> > macro, folding it into ...
> > (_GLIBCXX_DEBUG_VERIFY_AT_F): ... here. Do not use
> > __glibcxx_constexpr_assert.
> > * include/debug/safe_base.h (_Safe_iterator_base): Add constexpr
> > to some member functions. Omit attaching, detaching and checking
> > operations during constant evaluation.
> > * include/debug/safe_container.h (_Safe_container): Likewise.
> > * include/debug/safe_iterator.h (_Safe_iterator): Likewise.
> > * include/debug/safe_iterator.tcc (__niter_base, __copy_move_a)
> > (__copy_move_backward_a, __fill_a, __fill_n_a, __equal_aux)
> > (__lexicographical_compare_aux): Add constexpr.
> > * include/debug/vector (_Safe_vector, vector): Add constexpr.
> > Omit safe iterator operations during constant evaluation.
> > * testsuite/23_containers/vector/bool/capacity/constexpr.cc:
> > Remove dg-xfail-if for debug mode.
> > * testsuite/23_containers/vector/bool/cmp_c++20.cc: Likewise.
> > * testsuite/23_containers/vector/bool/cons/constexpr.cc:
> > Likewise.
> > * testsuite/23_containers/vector/bool/element_access/1.cc:
> > Likewise.
> > * testsuite/23_containers/vector/bool/element_access/constexpr.cc:
> > Likewise.
> > * testsuite/23_containers/vector/bool/modifiers/assign/constexpr.cc:
> > Likewise.
> > * testsuite/23_containers/vector/bool/modifiers/constexpr.cc:
> > Likewise.
> > * testsuite/23_containers/vector/bool/modifiers/swap/constexpr.cc:
> > Likewise.
> > * testsuite/23_containers/vector/capacity/constexpr.cc:
> > Likewise.
> > * testsuite/23_containers/vector/cmp_c++20.cc: Likewise.
> > * testsuite/23_containers/vector/cons/constexpr.cc: Likewise.
> > * testsuite/23_containers/vector/data_access/constexpr.cc:
> > Likewise.
> > * testsuite/23_containers/vector/element_access/constexpr.cc:
> > Likewise.
> > * testsuite/23_containers/vector/modifiers/assign/constexpr.cc:
> > Likewise.
> > * testsuite/23_containers/vector/modifiers/constexpr.cc:
> > Likewise.
> > * testsuite/23_containers/vector/modifiers/swap/constexpr.cc:
> > Likewise.
> > ---
> > libstdc++-v3/include/bits/c++config | 9 -
> > libstdc++-v3/include/bits/stl_algobase.h | 15 ++
> > libstdc++-v3/include/debug/helper_functions.h | 1 +
> > libstdc++-v3/include/debug/macros.h
Re: [PATCH] libstdc++: Make __gnu_debug::vector usable in constant expressions [PR109536]
On Wed, 6 Dec 2023, Jonathan Wakely wrote:
> Any comments on this approach?
>
> -- >8 --
>
> This makes constexpr std::vector (mostly) work in Debug Mode. All safe
> iterator instrumentation and checking is disabled during constant
> evaluation, because it requires mutex locks and calls to non-inline
> functions defined in libstdc++.so. It should be OK to disable the safety
> checks, because most UB should be detected during constant evaluation
> anyway.
>
> We could try to enable the full checking in constexpr, but it would mean
> wrapping all the non-inline functions like _M_attach with an inline
> _M_constexpr_attach that does the iterator housekeeping inline without
> mutex locks when calling for constant evaluation, and calls the
> non-inline function at runtime. That could be done in future if we find
> that we've lost safety or useful checking by disabling the safe
> iterators.
>
> There are a few test failures in C++20 mode, which I'm unable to
> explain. The _Safe_iterator::operator++() member gives errors for using
> non-constexpr functions during constant evaluation, even though those
> functions are guarded by std::is_constant_evaluated() checks. The same
> code works fine for C++23 and up.
AFAICT these C++20 test failures are really due to the variable
definition of non-literal type
381__gnu_cxx::__scoped_lock __l(this->_M_get_mutex());
which were prohibited in a constexpr function (even if that code was
never executed) until C++23's P2242R3.
We can use an immediately invoked lambda to work around this:
381[this] {
382 __gnu_cxx::__scoped_lock __l(this->_M_get_mutex());
383 ++base();
384}();
385return *this;
>
> libstdc++-v3/ChangeLog:
>
> PR libstdc++/109536
> * include/bits/c++config (__glibcxx_constexpr_assert): Remove
> macro.
> * include/bits/stl_algobase.h (__niter_base, __copy_move_a)
> (__copy_move_backward_a, __fill_a, __fill_n_a, __equal_aux)
> (__lexicographical_compare_aux): Add constexpr to overloads for
> debug mode iterators.
> * include/debug/helper_functions.h (__unsafe): Add constexpr.
> * include/debug/macros.h (_GLIBCXX_DEBUG_VERIFY_COND_AT): Remove
> macro, folding it into ...
> (_GLIBCXX_DEBUG_VERIFY_AT_F): ... here. Do not use
> __glibcxx_constexpr_assert.
> * include/debug/safe_base.h (_Safe_iterator_base): Add constexpr
> to some member functions. Omit attaching, detaching and checking
> operations during constant evaluation.
> * include/debug/safe_container.h (_Safe_container): Likewise.
> * include/debug/safe_iterator.h (_Safe_iterator): Likewise.
> * include/debug/safe_iterator.tcc (__niter_base, __copy_move_a)
> (__copy_move_backward_a, __fill_a, __fill_n_a, __equal_aux)
> (__lexicographical_compare_aux): Add constexpr.
> * include/debug/vector (_Safe_vector, vector): Add constexpr.
> Omit safe iterator operations during constant evaluation.
> * testsuite/23_containers/vector/bool/capacity/constexpr.cc:
> Remove dg-xfail-if for debug mode.
> * testsuite/23_containers/vector/bool/cmp_c++20.cc: Likewise.
> * testsuite/23_containers/vector/bool/cons/constexpr.cc:
> Likewise.
> * testsuite/23_containers/vector/bool/element_access/1.cc:
> Likewise.
> * testsuite/23_containers/vector/bool/element_access/constexpr.cc:
> Likewise.
> * testsuite/23_containers/vector/bool/modifiers/assign/constexpr.cc:
> Likewise.
> * testsuite/23_containers/vector/bool/modifiers/constexpr.cc:
> Likewise.
> * testsuite/23_containers/vector/bool/modifiers/swap/constexpr.cc:
> Likewise.
> * testsuite/23_containers/vector/capacity/constexpr.cc:
> Likewise.
> * testsuite/23_containers/vector/cmp_c++20.cc: Likewise.
> * testsuite/23_containers/vector/cons/constexpr.cc: Likewise.
> * testsuite/23_containers/vector/data_access/constexpr.cc:
> Likewise.
> * testsuite/23_containers/vector/element_access/constexpr.cc:
> Likewise.
> * testsuite/23_containers/vector/modifiers/assign/constexpr.cc:
> Likewise.
> * testsuite/23_containers/vector/modifiers/constexpr.cc:
> Likewise.
> * testsuite/23_containers/vector/modifiers/swap/constexpr.cc:
> Likewise.
> ---
> libstdc++-v3/include/bits/c++config | 9 -
> libstdc++-v3/include/bits/stl_algobase.h | 15 ++
> libstdc++-v3/include/debug/helper_functions.h | 1 +
> libstdc++-v3/include/debug/macros.h | 9 +-
> libstdc++-v3/include/debug/safe_base.h| 35 +++-
> libstdc++-v3/include/debug/safe_container.h | 15 +-
> libstdc++-v3/include/debug/safe_iterator.h| 186 +++---
> libstdc++-v3/include/debug/safe_iterator.tcc | 15 ++
> libstdc++-v3/include/debug/vector | 146 --
> .../vector/bool/capacity/constexpr.cc | 1 -
>
Re: [PATCH] libstdc++: Make __gnu_debug::vector usable in constant expressions [PR109536]
On Wed, 6 Dec 2023 at 14:30, Jonathan Wakely wrote: > > Any comments on this approach? Pushed to trunk now. > > -- >8 -- > > This makes constexpr std::vector (mostly) work in Debug Mode. All safe > iterator instrumentation and checking is disabled during constant > evaluation, because it requires mutex locks and calls to non-inline > functions defined in libstdc++.so. It should be OK to disable the safety > checks, because most UB should be detected during constant evaluation > anyway. > > We could try to enable the full checking in constexpr, but it would mean > wrapping all the non-inline functions like _M_attach with an inline > _M_constexpr_attach that does the iterator housekeeping inline without > mutex locks when calling for constant evaluation, and calls the > non-inline function at runtime. That could be done in future if we find > that we've lost safety or useful checking by disabling the safe > iterators. > > There are a few test failures in C++20 mode, which I'm unable to > explain. The _Safe_iterator::operator++() member gives errors for using > non-constexpr functions during constant evaluation, even though those > functions are guarded by std::is_constant_evaluated() checks. The same > code works fine for C++23 and up. > > libstdc++-v3/ChangeLog: > > PR libstdc++/109536 > * include/bits/c++config (__glibcxx_constexpr_assert): Remove > macro. > * include/bits/stl_algobase.h (__niter_base, __copy_move_a) > (__copy_move_backward_a, __fill_a, __fill_n_a, __equal_aux) > (__lexicographical_compare_aux): Add constexpr to overloads for > debug mode iterators. > * include/debug/helper_functions.h (__unsafe): Add constexpr. > * include/debug/macros.h (_GLIBCXX_DEBUG_VERIFY_COND_AT): Remove > macro, folding it into ... > (_GLIBCXX_DEBUG_VERIFY_AT_F): ... here. Do not use > __glibcxx_constexpr_assert. > * include/debug/safe_base.h (_Safe_iterator_base): Add constexpr > to some member functions. Omit attaching, detaching and checking > operations during constant evaluation. > * include/debug/safe_container.h (_Safe_container): Likewise. > * include/debug/safe_iterator.h (_Safe_iterator): Likewise. > * include/debug/safe_iterator.tcc (__niter_base, __copy_move_a) > (__copy_move_backward_a, __fill_a, __fill_n_a, __equal_aux) > (__lexicographical_compare_aux): Add constexpr. > * include/debug/vector (_Safe_vector, vector): Add constexpr. > Omit safe iterator operations during constant evaluation. > * testsuite/23_containers/vector/bool/capacity/constexpr.cc: > Remove dg-xfail-if for debug mode. > * testsuite/23_containers/vector/bool/cmp_c++20.cc: Likewise. > * testsuite/23_containers/vector/bool/cons/constexpr.cc: > Likewise. > * testsuite/23_containers/vector/bool/element_access/1.cc: > Likewise. > * testsuite/23_containers/vector/bool/element_access/constexpr.cc: > Likewise. > * testsuite/23_containers/vector/bool/modifiers/assign/constexpr.cc: > Likewise. > * testsuite/23_containers/vector/bool/modifiers/constexpr.cc: > Likewise. > * testsuite/23_containers/vector/bool/modifiers/swap/constexpr.cc: > Likewise. > * testsuite/23_containers/vector/capacity/constexpr.cc: > Likewise. > * testsuite/23_containers/vector/cmp_c++20.cc: Likewise. > * testsuite/23_containers/vector/cons/constexpr.cc: Likewise. > * testsuite/23_containers/vector/data_access/constexpr.cc: > Likewise. > * testsuite/23_containers/vector/element_access/constexpr.cc: > Likewise. > * testsuite/23_containers/vector/modifiers/assign/constexpr.cc: > Likewise. > * testsuite/23_containers/vector/modifiers/constexpr.cc: > Likewise. > * testsuite/23_containers/vector/modifiers/swap/constexpr.cc: > Likewise. > --- > libstdc++-v3/include/bits/c++config | 9 - > libstdc++-v3/include/bits/stl_algobase.h | 15 ++ > libstdc++-v3/include/debug/helper_functions.h | 1 + > libstdc++-v3/include/debug/macros.h | 9 +- > libstdc++-v3/include/debug/safe_base.h| 35 +++- > libstdc++-v3/include/debug/safe_container.h | 15 +- > libstdc++-v3/include/debug/safe_iterator.h| 186 +++--- > libstdc++-v3/include/debug/safe_iterator.tcc | 15 ++ > libstdc++-v3/include/debug/vector | 146 -- > .../vector/bool/capacity/constexpr.cc | 1 - > .../23_containers/vector/bool/cmp_c++20.cc| 1 - > .../vector/bool/cons/constexpr.cc | 1 - > .../vector/bool/element_access/1.cc | 1 - > .../vector/bool/element_access/constexpr.cc | 1 - > .../vector/bool/modifiers/assign/constexpr.cc | 1 - > .../vector/bool/modifiers/constexpr.cc| 1
