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* [Bug libstdc++/100479] New: range adaptors handle cached iterators incorrectly
@ 2021-05-07 23:04 rs2740 at gmail dot com
2021-05-07 23:09 ` [Bug libstdc++/100479] " redi at gcc dot gnu.org
` (4 more replies)
0 siblings, 5 replies; 6+ messages in thread
From: rs2740 at gmail dot com @ 2021-05-07 23:04 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100479
Bug ID: 100479
Summary: range adaptors handle cached iterators incorrectly
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: rs2740 at gmail dot com
Target Milestone: ---
template<forward_range _Range>
struct _CachedPosition<_Range>
{
private:
iterator_t<_Range> _M_iter{};
public:
constexpr bool
_M_has_value() const
{ return _M_iter != iterator_t<_Range>{}; }
constexpr iterator_t<_Range>
_M_get(const _Range&) const
{
__glibcxx_assert(_M_has_value());
return _M_iter;
}
constexpr void
_M_set(const _Range&, const iterator_t<_Range>& __it)
{
__glibcxx_assert(!_M_has_value());
_M_iter = __it;
}
};
- The domain of == for forward iterators is limited to iterators over the same
underlying sequence. While value-initialized forward iterators of the same type
may be compared against each other, comparing them against iterators into other
ranges is not required to be well-defined, so it cannot be used as a sentinel
value.
- The cache cannot be allowed to propagate when the view containing it is
copied/moved, and has to be invalidated when the view containing it is moved.
Any cached iterator points to the original underlying view, and not the new
one; also, moving from a view can change its value (if it is well-defined to
use the moved-from view), so the cache is no longer valid. (Handling this case
correctly was actually the original use case for non-propagating-cache in
range-v3.)
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug libstdc++/100479] range adaptors handle cached iterators incorrectly
2021-05-07 23:04 [Bug libstdc++/100479] New: range adaptors handle cached iterators incorrectly rs2740 at gmail dot com
@ 2021-05-07 23:09 ` redi at gcc dot gnu.org
2021-05-11 15:28 ` ppalka at gcc dot gnu.org
` (3 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: redi at gcc dot gnu.org @ 2021-05-07 23:09 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100479
Jonathan Wakely <redi at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Ever confirmed|0 |1
Last reconfirmed| |2021-05-07
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug libstdc++/100479] range adaptors handle cached iterators incorrectly
2021-05-07 23:04 [Bug libstdc++/100479] New: range adaptors handle cached iterators incorrectly rs2740 at gmail dot com
2021-05-07 23:09 ` [Bug libstdc++/100479] " redi at gcc dot gnu.org
@ 2021-05-11 15:28 ` ppalka at gcc dot gnu.org
2021-05-24 19:24 ` cvs-commit at gcc dot gnu.org
` (2 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: ppalka at gcc dot gnu.org @ 2021-05-11 15:28 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100479
Patrick Palka <ppalka at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Assignee|unassigned at gcc dot gnu.org |ppalka at gcc dot gnu.org
Status|NEW |ASSIGNED
CC| |ppalka at gcc dot gnu.org
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug libstdc++/100479] range adaptors handle cached iterators incorrectly
2021-05-07 23:04 [Bug libstdc++/100479] New: range adaptors handle cached iterators incorrectly rs2740 at gmail dot com
2021-05-07 23:09 ` [Bug libstdc++/100479] " redi at gcc dot gnu.org
2021-05-11 15:28 ` ppalka at gcc dot gnu.org
@ 2021-05-24 19:24 ` cvs-commit at gcc dot gnu.org
2021-05-28 14:21 ` cvs-commit at gcc dot gnu.org
2021-10-12 19:00 ` ppalka at gcc dot gnu.org
4 siblings, 0 replies; 6+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2021-05-24 19:24 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100479
--- Comment #1 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Patrick Palka <ppalka@gcc.gnu.org>:
https://gcc.gnu.org/g:46ed811bcb4b86a81ef3d78ea8cfffc6cd043144
commit r12-1018-g46ed811bcb4b86a81ef3d78ea8cfffc6cd043144
Author: Patrick Palka <ppalka@redhat.com>
Date: Mon May 24 15:24:44 2021 -0400
libstdc++: Fix iterator caching inside range adaptors [PR100479]
This fixes two issues with our iterator caching as described in detail
in the PR. Since we recently added the __non_propagating_cache class
template as part of r12-336 for P2328, this patch just rewrites the
problematic _CachedPosition partial specialization in terms of this
class template.
For the offset partial specialization, it's safe to propagate the cached
offset on copy/move, but we should still invalidate the cached offset in
the source object on move.
libstdc++-v3/ChangeLog:
PR libstdc++/100479
* include/std/ranges (__detail::__non_propagating_cache): Move
definition up to before that of _CachedPosition. Make base
class _Optional_base protected instead of private. Add const
overload for operator*.
(__detail::_CachedPosition): Rewrite the partial specialization
for forward ranges as a derived class of __non_propagating_cache.
Remove the size constraint on the partial specialization for
random access ranges. Add
copy/move/copy-assignment/move-assignment
members to the offset partial specialization for random
access ranges that propagate the cached value but additionally
invalidate it in the source object on move.
* testsuite/std/ranges/adaptors/100479.cc: New test.
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug libstdc++/100479] range adaptors handle cached iterators incorrectly
2021-05-07 23:04 [Bug libstdc++/100479] New: range adaptors handle cached iterators incorrectly rs2740 at gmail dot com
` (2 preceding siblings ...)
2021-05-24 19:24 ` cvs-commit at gcc dot gnu.org
@ 2021-05-28 14:21 ` cvs-commit at gcc dot gnu.org
2021-10-12 19:00 ` ppalka at gcc dot gnu.org
4 siblings, 0 replies; 6+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2021-05-28 14:21 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100479
--- Comment #2 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-11 branch has been updated by Patrick Palka
<ppalka@gcc.gnu.org>:
https://gcc.gnu.org/g:49f369fb33fb5bed4dadfb5b42b23cded888ab52
commit r11-8476-g49f369fb33fb5bed4dadfb5b42b23cded888ab52
Author: Patrick Palka <ppalka@redhat.com>
Date: Mon May 24 15:24:44 2021 -0400
libstdc++: Fix iterator caching inside range adaptors [PR100479]
This fixes two issues with our iterator caching as described in detail
in the PR. Since we recently added the __non_propagating_cache class
template as part of r12-336 for P2328, this patch just rewrites the
problematic _CachedPosition partial specialization in terms of this
class template.
For the offset partial specialization, it's safe to propagate the cached
offset on copy/move, but we should still invalidate the cached offset in
the source object on move.
libstdc++-v3/ChangeLog:
PR libstdc++/100479
* include/std/ranges (__detail::__non_propagating_cache): Move
definition up to before that of _CachedPosition. Make base
class _Optional_base protected instead of private. Add const
overload for operator*.
(__detail::_CachedPosition): Rewrite the partial specialization
for forward ranges as a derived class of __non_propagating_cache.
Remove the size constraint on the partial specialization for
random access ranges. Add
copy/move/copy-assignment/move-assignment
members to the offset partial specialization for random
access ranges that propagate the cached value but additionally
invalidate it in the source object on move.
* testsuite/std/ranges/adaptors/100479.cc: New test.
(cherry picked from commit 46ed811bcb4b86a81ef3d78ea8cfffc6cd043144)
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug libstdc++/100479] range adaptors handle cached iterators incorrectly
2021-05-07 23:04 [Bug libstdc++/100479] New: range adaptors handle cached iterators incorrectly rs2740 at gmail dot com
` (3 preceding siblings ...)
2021-05-28 14:21 ` cvs-commit at gcc dot gnu.org
@ 2021-10-12 19:00 ` ppalka at gcc dot gnu.org
4 siblings, 0 replies; 6+ messages in thread
From: ppalka at gcc dot gnu.org @ 2021-10-12 19:00 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100479
Patrick Palka <ppalka at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|--- |11.2
Status|ASSIGNED |RESOLVED
Resolution|--- |FIXED
--- Comment #3 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Fixed for 11.2/12
^ permalink raw reply [flat|nested] 6+ messages in thread
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2021-05-07 23:04 [Bug libstdc++/100479] New: range adaptors handle cached iterators incorrectly rs2740 at gmail dot com
2021-05-07 23:09 ` [Bug libstdc++/100479] " redi at gcc dot gnu.org
2021-05-11 15:28 ` ppalka at gcc dot gnu.org
2021-05-24 19:24 ` cvs-commit at gcc dot gnu.org
2021-05-28 14:21 ` cvs-commit at gcc dot gnu.org
2021-10-12 19:00 ` ppalka at gcc dot gnu.org
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