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* [Bug libstdc++/100894] New: The std::common_reference implementation seems to be wrong
@ 2021-06-03 16:35 hewillk at gmail dot com
2021-06-14 17:25 ` [Bug libstdc++/100894] " redi at gcc dot gnu.org
` (5 more replies)
0 siblings, 6 replies; 7+ messages in thread
From: hewillk at gmail dot com @ 2021-06-03 16:35 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100894
Bug ID: 100894
Summary: The std::common_reference implementation seems to be
wrong
Product: gcc
Version: 12.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: hewillk at gmail dot com
Target Milestone: ---
In [meta#trans.other-6.3.1], the standard specifies "If T1 and T2 are reference
types and COMMON-REF(T1, T2) is well-formed, then the member typedef type
denotes that type", where COMMON-REF is defined in [meta#trans.other-3.5]: "If
A and B are both lvalue reference types, COMMON-REF(A, B) is COND-RES(COPYCV(X,
Y) &, COPYCV( Y, X) &) if that type exists and is a reference type."
libstdc++ does not check that COMMON-REF(A, B) must be a reference type, which
will lead to incorrect determination of the common reference type according to
bullet 1 in the following cases.
https://godbolt.org/z/7Mc7jjesK
#include <concepts>
struct A {};
struct B { B(A); };
static_assert(
std::same_as<
std::common_reference_t<A&, B&&>, B>);
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug libstdc++/100894] The std::common_reference implementation seems to be wrong
2021-06-03 16:35 [Bug libstdc++/100894] New: The std::common_reference implementation seems to be wrong hewillk at gmail dot com
@ 2021-06-14 17:25 ` redi at gcc dot gnu.org
2021-06-14 19:30 ` redi at gcc dot gnu.org
` (4 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: redi at gcc dot gnu.org @ 2021-06-14 17:25 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100894
Jonathan Wakely <redi at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Ever confirmed|0 |1
Assignee|unassigned at gcc dot gnu.org |redi at gcc dot gnu.org
Status|UNCONFIRMED |ASSIGNED
Last reconfirmed| |2021-06-14
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug libstdc++/100894] The std::common_reference implementation seems to be wrong
2021-06-03 16:35 [Bug libstdc++/100894] New: The std::common_reference implementation seems to be wrong hewillk at gmail dot com
2021-06-14 17:25 ` [Bug libstdc++/100894] " redi at gcc dot gnu.org
@ 2021-06-14 19:30 ` redi at gcc dot gnu.org
2021-06-14 20:17 ` cvs-commit at gcc dot gnu.org
` (3 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: redi at gcc dot gnu.org @ 2021-06-14 19:30 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100894
Jonathan Wakely <redi at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|--- |10.4
--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
For the next time I can't figure out how this works ...
COMMON-REF(A&, B&&) is COMMON-REF(B&&, A&) which is COMMON-REF(const B&, A&)
which is COND-RES(const B&, const A&) if that is a reference type, ill-formed
otherwise. Since the COND-RES type is just B, it's ill-formed.
That means that common_reference_t<A&, B&&> uses the third bullet, so it's
COND-RES(A&, B&&) which is B.
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug libstdc++/100894] The std::common_reference implementation seems to be wrong
2021-06-03 16:35 [Bug libstdc++/100894] New: The std::common_reference implementation seems to be wrong hewillk at gmail dot com
2021-06-14 17:25 ` [Bug libstdc++/100894] " redi at gcc dot gnu.org
2021-06-14 19:30 ` redi at gcc dot gnu.org
@ 2021-06-14 20:17 ` cvs-commit at gcc dot gnu.org
2021-06-14 21:49 ` cvs-commit at gcc dot gnu.org
` (2 subsequent siblings)
5 siblings, 0 replies; 7+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2021-06-14 20:17 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100894
--- Comment #2 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Jonathan Wakely <redi@gcc.gnu.org>:
https://gcc.gnu.org/g:c37b5ddcc88e0cc0f6a4ad609eda51021df0f6bb
commit r12-1437-gc37b5ddcc88e0cc0f6a4ad609eda51021df0f6bb
Author: Jonathan Wakely <jwakely@redhat.com>
Date: Mon Jun 14 20:31:00 2021 +0100
libstdc++: Fix common_reference for non-reference results [PR100894]
The result of COMMON-REF(A&, B&&) where they have no common reference
type should not be a reference. The implementation of COMMON-REF fails
to check that the result is a reference, so is well-formed when it
shouldn't be. This means that common_reference uses that result when it
shouldn't.
The fix is to reject the result of COMMON-REF(A, B) if it's not a
reference, so that common_reference falls through to the next case,
which uses COND-RES, which yields a non-reference result.
Signed-off-by: Jonathan Wakely <jwakely@redhat.com>
libstdc++-v3/ChangeLog:
PR libstdc++/100894
* include/std/type_traits (__common_ref_impl<X&, Y&>): Only
use the type if it's a reference.
* testsuite/20_util/common_reference/100894.cc: New test.
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug libstdc++/100894] The std::common_reference implementation seems to be wrong
2021-06-03 16:35 [Bug libstdc++/100894] New: The std::common_reference implementation seems to be wrong hewillk at gmail dot com
` (2 preceding siblings ...)
2021-06-14 20:17 ` cvs-commit at gcc dot gnu.org
@ 2021-06-14 21:49 ` cvs-commit at gcc dot gnu.org
2021-08-10 16:07 ` cvs-commit at gcc dot gnu.org
2021-08-10 16:07 ` redi at gcc dot gnu.org
5 siblings, 0 replies; 7+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2021-06-14 21:49 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100894
--- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-11 branch has been updated by Jonathan Wakely
<redi@gcc.gnu.org>:
https://gcc.gnu.org/g:3ae416e0a77a000b536171dbe06c3c2d136fb8e1
commit r11-8572-g3ae416e0a77a000b536171dbe06c3c2d136fb8e1
Author: Jonathan Wakely <jwakely@redhat.com>
Date: Mon Jun 14 20:31:00 2021 +0100
libstdc++: Fix common_reference for non-reference results [PR100894]
The result of COMMON-REF(A&, B&&) where they have no common reference
type should be ill-formed. Our implementation fails to check that the
COMMON-REF result is a reference, so is well-formed when it shouldn't
be. This means that common_reference uses that result when it shouldn't
do.
The fix is to reject the result of COMMON-REF(A, B) if it's not a
reference, so that common_reference falls through to the next case,
which uses COND-RES, which yields the correct non-reference result.
Signed-off-by: Jonathan Wakely <jwakely@redhat.com>
libstdc++-v3/ChangeLog:
PR libstdc++/100894
* include/std/type_traits (__common_ref_impl<X&, Y&>): Only
use the type if it's a reference.
* testsuite/20_util/common_reference/100894.cc: New test.
(cherry picked from commit c37b5ddcc88e0cc0f6a4ad609eda51021df0f6bb)
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug libstdc++/100894] The std::common_reference implementation seems to be wrong
2021-06-03 16:35 [Bug libstdc++/100894] New: The std::common_reference implementation seems to be wrong hewillk at gmail dot com
` (3 preceding siblings ...)
2021-06-14 21:49 ` cvs-commit at gcc dot gnu.org
@ 2021-08-10 16:07 ` cvs-commit at gcc dot gnu.org
2021-08-10 16:07 ` redi at gcc dot gnu.org
5 siblings, 0 replies; 7+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2021-08-10 16:07 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100894
--- Comment #4 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The releases/gcc-10 branch has been updated by Jonathan Wakely
<redi@gcc.gnu.org>:
https://gcc.gnu.org/g:0e54986854831a4c66b308f98aff949ca7d3ce84
commit r10-10026-g0e54986854831a4c66b308f98aff949ca7d3ce84
Author: Jonathan Wakely <jwakely@redhat.com>
Date: Mon Jun 14 20:31:00 2021 +0100
libstdc++: Fix common_reference for non-reference results [PR100894]
The result of COMMON-REF(A&, B&&) where they have no common reference
type should be ill-formed. Our implementation fails to check that the
COMMON-REF result is a reference, so is well-formed when it shouldn't
be. This means that common_reference uses that result when it shouldn't
do.
The fix is to reject the result of COMMON-REF(A, B) if it's not a
reference, so that common_reference falls through to the next case,
which uses COND-RES, which yields the correct non-reference result.
Signed-off-by: Jonathan Wakely <jwakely@redhat.com>
libstdc++-v3/ChangeLog:
PR libstdc++/100894
* include/std/type_traits (__common_ref_impl<X&, Y&>): Only
use the type if it's a reference.
* testsuite/20_util/common_reference/100894.cc: New test.
(cherry picked from commit c37b5ddcc88e0cc0f6a4ad609eda51021df0f6bb)
^ permalink raw reply [flat|nested] 7+ messages in thread
* [Bug libstdc++/100894] The std::common_reference implementation seems to be wrong
2021-06-03 16:35 [Bug libstdc++/100894] New: The std::common_reference implementation seems to be wrong hewillk at gmail dot com
` (4 preceding siblings ...)
2021-08-10 16:07 ` cvs-commit at gcc dot gnu.org
@ 2021-08-10 16:07 ` redi at gcc dot gnu.org
5 siblings, 0 replies; 7+ messages in thread
From: redi at gcc dot gnu.org @ 2021-08-10 16:07 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100894
Jonathan Wakely <redi at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Resolution|--- |FIXED
Status|ASSIGNED |RESOLVED
--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Fixed for 10.4 and 11.2, thanks
^ permalink raw reply [flat|nested] 7+ messages in thread
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2021-06-03 16:35 [Bug libstdc++/100894] New: The std::common_reference implementation seems to be wrong hewillk at gmail dot com
2021-06-14 17:25 ` [Bug libstdc++/100894] " redi at gcc dot gnu.org
2021-06-14 19:30 ` redi at gcc dot gnu.org
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