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* [Bug c++/96223] New: DR 1787 and indeterminate values in constexpr context
@ 2020-07-16 19:30 mpolacek at gcc dot gnu.org
2020-07-16 19:32 ` [Bug c++/96223] " mpolacek at gcc dot gnu.org
` (4 more replies)
0 siblings, 5 replies; 6+ messages in thread
From: mpolacek at gcc dot gnu.org @ 2020-07-16 19:30 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96223
Bug ID: 96223
Summary: DR 1787 and indeterminate values in constexpr context
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: mpolacek at gcc dot gnu.org
Target Milestone: ---
Use -std=c++20:
// DR 1787
#include <cstddef>
constexpr int
fn1 ()
{
unsigned char foo;
unsigned char u = foo; // OK: u has an indeterminate value
return u; // UB: copy-init -> standard conversion to int
}
constexpr int
fn2 ()
{
unsigned char foo;
int i = foo; // UB
return 0;
}
constexpr int
fn3 ()
{
unsigned char foo;
char8_t u = foo; // UB: char8_t not an unsigned ordinary character type
return 0;
}
constexpr int
fn4 ()
{
std::byte foo;
std::byte b = foo; // OK
return 0;
}
constexpr int w1 = fn1 ();
constexpr int w2 = fn2 ();
constexpr int w3 = fn3 ();
constexpr int w4 = fn4 ();
DR 1787 says that if an indeterminate value is produced by an evaluation, the
behavior is undefined except in certain cases. In fn1 and fn4 we issue errors
even for some of the "certain cases" (the lines marked with OK) and I think
it's a bug. Uninitialized variables in a constexpr context are OK since C++20
P1331R2.
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug c++/96223] DR 1787 and indeterminate values in constexpr context
2020-07-16 19:30 [Bug c++/96223] New: DR 1787 and indeterminate values in constexpr context mpolacek at gcc dot gnu.org
@ 2020-07-16 19:32 ` mpolacek at gcc dot gnu.org
2020-08-06 17:54 ` richard-gccbugzilla at metafoo dot co.uk
` (3 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: mpolacek at gcc dot gnu.org @ 2020-07-16 19:32 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96223
--- Comment #1 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Note that is_byte_access_type won't do, because it includes char8_t too.
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug c++/96223] DR 1787 and indeterminate values in constexpr context
2020-07-16 19:30 [Bug c++/96223] New: DR 1787 and indeterminate values in constexpr context mpolacek at gcc dot gnu.org
2020-07-16 19:32 ` [Bug c++/96223] " mpolacek at gcc dot gnu.org
@ 2020-08-06 17:54 ` richard-gccbugzilla at metafoo dot co.uk
2020-08-06 18:00 ` mpolacek at gcc dot gnu.org
` (2 subsequent siblings)
4 siblings, 0 replies; 6+ messages in thread
From: richard-gccbugzilla at metafoo dot co.uk @ 2020-08-06 17:54 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96223
Richard Smith <richard-gccbugzilla at metafoo dot co.uk> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |richard-gccbugzilla@metafoo
| |.co.uk
--- Comment #2 from Richard Smith <richard-gccbugzilla at metafoo dot co.uk> ---
P1331R2 explicitly disallows in a constant evaluation:
"- an lvalue-to-rvalue conversion that is applied to an object with
indeterminate value ([basic.indet]);"
so GCC is correct to reject such cases.
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug c++/96223] DR 1787 and indeterminate values in constexpr context
2020-07-16 19:30 [Bug c++/96223] New: DR 1787 and indeterminate values in constexpr context mpolacek at gcc dot gnu.org
2020-07-16 19:32 ` [Bug c++/96223] " mpolacek at gcc dot gnu.org
2020-08-06 17:54 ` richard-gccbugzilla at metafoo dot co.uk
@ 2020-08-06 18:00 ` mpolacek at gcc dot gnu.org
2020-09-17 20:15 ` cvs-commit at gcc dot gnu.org
2020-09-17 20:19 ` mpolacek at gcc dot gnu.org
4 siblings, 0 replies; 6+ messages in thread
From: mpolacek at gcc dot gnu.org @ 2020-08-06 18:00 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96223
Marek Polacek <mpolacek at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords|rejects-valid |
Assignee|unassigned at gcc dot gnu.org |mpolacek at gcc dot gnu.org
Last reconfirmed| |2020-08-06
Status|UNCONFIRMED |ASSIGNED
Ever confirmed|0 |1
--- Comment #3 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Aaah, I see. Thanks a lot!
I'll add the test at least.
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug c++/96223] DR 1787 and indeterminate values in constexpr context
2020-07-16 19:30 [Bug c++/96223] New: DR 1787 and indeterminate values in constexpr context mpolacek at gcc dot gnu.org
` (2 preceding siblings ...)
2020-08-06 18:00 ` mpolacek at gcc dot gnu.org
@ 2020-09-17 20:15 ` cvs-commit at gcc dot gnu.org
2020-09-17 20:19 ` mpolacek at gcc dot gnu.org
4 siblings, 0 replies; 6+ messages in thread
From: cvs-commit at gcc dot gnu.org @ 2020-09-17 20:15 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96223
--- Comment #4 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Marek Polacek <mpolacek@gcc.gnu.org>:
https://gcc.gnu.org/g:4f0aa5b051c0d3e81478bcb495e4e072b2d9827d
commit r11-3268-g4f0aa5b051c0d3e81478bcb495e4e072b2d9827d
Author: Marek Polacek <polacek@redhat.com>
Date: Thu Sep 17 15:31:50 2020 -0400
c++: Add tests for fixed PRs.
Bugzilla inspection turned up a bunch of old(er) PRs that have been
fixed. Let's include them not to regress in the future.
gcc/testsuite/ChangeLog:
PR c++/87530
PR c++/58156
PR c++/68828
PR c++/86002
PR c++/91525
PR c++/96223
PR c++/87032
PR c++/35098
* g++.dg/cpp0x/move-return4.C: New test.
* g++.dg/cpp0x/vt-58156.C: New test.
* g++.dg/cpp2a/concepts-pr68828.C: New test.
* g++.dg/cpp2a/concepts-pr86002.C: New test.
* g++.dg/cpp2a/concepts-pr91525.C: New test.
* g++.dg/cpp2a/constexpr-indeterminate1.C: New test.
* g++.dg/cpp2a/desig17.C: New test.
* g++.dg/ext/attrib62.C: New test.
^ permalink raw reply [flat|nested] 6+ messages in thread
* [Bug c++/96223] DR 1787 and indeterminate values in constexpr context
2020-07-16 19:30 [Bug c++/96223] New: DR 1787 and indeterminate values in constexpr context mpolacek at gcc dot gnu.org
` (3 preceding siblings ...)
2020-09-17 20:15 ` cvs-commit at gcc dot gnu.org
@ 2020-09-17 20:19 ` mpolacek at gcc dot gnu.org
4 siblings, 0 replies; 6+ messages in thread
From: mpolacek at gcc dot gnu.org @ 2020-09-17 20:19 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96223
Marek Polacek <mpolacek at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Resolution|--- |FIXED
Status|ASSIGNED |RESOLVED
--- Comment #5 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Test added.
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2020-09-17 20:19 UTC | newest]
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2020-07-16 19:30 [Bug c++/96223] New: DR 1787 and indeterminate values in constexpr context mpolacek at gcc dot gnu.org
2020-07-16 19:32 ` [Bug c++/96223] " mpolacek at gcc dot gnu.org
2020-08-06 17:54 ` richard-gccbugzilla at metafoo dot co.uk
2020-08-06 18:00 ` mpolacek at gcc dot gnu.org
2020-09-17 20:15 ` cvs-commit at gcc dot gnu.org
2020-09-17 20:19 ` mpolacek at gcc dot gnu.org
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