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* [Bug libstdc++/107572] New: cartesian_product_view invokes the begin of input_range twice
@ 2022-11-08 15:25 hewillk at gmail dot com
2022-11-08 15:35 ` [Bug libstdc++/107572] " redi at gcc dot gnu.org
` (3 more replies)
0 siblings, 4 replies; 5+ messages in thread
From: hewillk at gmail dot com @ 2022-11-08 15:25 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107572
Bug ID: 107572
Summary: cartesian_product_view invokes the begin of
input_range twice
Product: gcc
Version: 13.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: hewillk at gmail dot com
Target Milestone: ---
ranges#L8069:
auto __it = __detail::__tuple_transform(ranges::begin, _M_bases);
if (!__empty_tail)
std::get<0>(__it) =
__detail::__cartesian_common_arg_end(std::get<0>(_M_bases));
return _Iterator<false>{*this, std::move(__it)};
This *always* invokes begin twice for the first range, which is undefined
behavior when it is an input_range.
testcase (https://godbolt.org/z/7hfP8xM6a):
#include <ranges>
#include <fmt/ranges.h>
#include <sstream>
std::istringstream ints("0 1 2 3 4");
struct istream_range {
auto begin() { return std::istream_iterator<int>{ints}; }
auto end() { return std::istream_iterator<int>{}; }
};
int main() {
istream_range r;
fmt::print("{}\n", std::views::cartesian_product(r)); // prints [(0),
(2), (3), (4)]
}
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug libstdc++/107572] cartesian_product_view invokes the begin of input_range twice
2022-11-08 15:25 [Bug libstdc++/107572] New: cartesian_product_view invokes the begin of input_range twice hewillk at gmail dot com
@ 2022-11-08 15:35 ` redi at gcc dot gnu.org
2023-03-07 21:07 ` ppalka at gcc dot gnu.org
` (2 subsequent siblings)
3 siblings, 0 replies; 5+ messages in thread
From: redi at gcc dot gnu.org @ 2022-11-08 15:35 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107572
Jonathan Wakely <redi at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |ppalka at gcc dot gnu.org
Ever confirmed|0 |1
Last reconfirmed| |2022-11-08
Status|UNCONFIRMED |NEW
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug libstdc++/107572] cartesian_product_view invokes the begin of input_range twice
2022-11-08 15:25 [Bug libstdc++/107572] New: cartesian_product_view invokes the begin of input_range twice hewillk at gmail dot com
2022-11-08 15:35 ` [Bug libstdc++/107572] " redi at gcc dot gnu.org
@ 2023-03-07 21:07 ` ppalka at gcc dot gnu.org
2023-03-09 18:25 ` cvs-commit at gcc dot gnu.org
2023-03-09 18:27 ` ppalka at gcc dot gnu.org
3 siblings, 0 replies; 5+ messages in thread
From: ppalka at gcc dot gnu.org @ 2023-03-07 21:07 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107572
Patrick Palka <ppalka at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |ASSIGNED
Assignee|unassigned at gcc dot gnu.org |ppalka at gcc dot gnu.org
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug libstdc++/107572] cartesian_product_view invokes the begin of input_range twice
2022-11-08 15:25 [Bug libstdc++/107572] New: cartesian_product_view invokes the begin of input_range twice hewillk at gmail dot com
2022-11-08 15:35 ` [Bug libstdc++/107572] " redi at gcc dot gnu.org
2023-03-07 21:07 ` ppalka at gcc dot gnu.org
@ 2023-03-09 18:25 ` cvs-commit at gcc dot gnu.org
2023-03-09 18:27 ` ppalka at gcc dot gnu.org
3 siblings, 0 replies; 5+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2023-03-09 18:25 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107572
--- 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:3df9760d56662bdf38dd45f7398f003bbd64fdfe
commit r13-6558-g3df9760d56662bdf38dd45f7398f003bbd64fdfe
Author: Patrick Palka <ppalka@redhat.com>
Date: Thu Mar 9 13:25:44 2023 -0500
libstdc++: extraneous begin in cartesian_product_view::end [PR107572]
ranges::begin() isn't guaranteed to be equality-preserving for non-forward
ranges, so in cartesian_product_view::end we need to avoid needlessly
calling begin() on the first range (which could be non-forward) in the
case where __empty_tail is false as per its specification.
Since we're already using a variadic lambda to compute __empty_tail, we
might as well use that same lambda to build up the tuple of iterators
instead of building it separately via e.g. std::apply or __tuple_transform.
PR libstdc++/107572
libstdc++-v3/ChangeLog:
* include/std/ranges (cartesian_product_view::end): When
building the tuple of iterators, avoid calling ranges::begin on
the first range if __empty_tail is false.
* testsuite/std/ranges/cartesian_product/1.cc (test07): New test.
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug libstdc++/107572] cartesian_product_view invokes the begin of input_range twice
2022-11-08 15:25 [Bug libstdc++/107572] New: cartesian_product_view invokes the begin of input_range twice hewillk at gmail dot com
` (2 preceding siblings ...)
2023-03-09 18:25 ` cvs-commit at gcc dot gnu.org
@ 2023-03-09 18:27 ` ppalka at gcc dot gnu.org
3 siblings, 0 replies; 5+ messages in thread
From: ppalka at gcc dot gnu.org @ 2023-03-09 18:27 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107572
Patrick Palka <ppalka at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|--- |13.0
Status|ASSIGNED |RESOLVED
Resolution|--- |FIXED
--- Comment #2 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Should be fixed, thanks for catching this.
^ permalink raw reply [flat|nested] 5+ messages in thread
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2022-11-08 15:25 [Bug libstdc++/107572] New: cartesian_product_view invokes the begin of input_range twice hewillk at gmail dot com
2022-11-08 15:35 ` [Bug libstdc++/107572] " redi at gcc dot gnu.org
2023-03-07 21:07 ` ppalka at gcc dot gnu.org
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