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* [Bug c++/110401] New: Unhelpful "goto is not a constant expression" in ill-formed constexpr function template
@ 2023-06-25 8:56 xry111 at gcc dot gnu.org
2023-06-25 13:15 ` [Bug c++/110401] [10/11/12/13/14 Regression] Unhelpful "goto is not a constant expression" in ill-formed pre c++20 " pinskia at gcc dot gnu.org
` (3 more replies)
0 siblings, 4 replies; 5+ messages in thread
From: xry111 at gcc dot gnu.org @ 2023-06-25 8:56 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110401
Bug ID: 110401
Summary: Unhelpful "goto is not a constant expression" in
ill-formed constexpr function template
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: xry111 at gcc dot gnu.org
Target Milestone: ---
#include <array>
template <int N>
constexpr std::array<int, N> get_sqr()
{
std::array<int, N> ret;
for (int i = 0; i < N; i++)
ret[i] = i * i;
return ret;
}
constexpr auto sqr = get_sqr<10000>();
GCC says "error: 'goto' is not a constant expression". This is puzzling
because there is no "goto" in the function.
Note that if it's not a template, GCC outputs the correct message:
#include <array>
constexpr std::array<int, 10000> get_sqr()
{
std::array<int, 10000> ret;
for (int i = 0; i < 10000; i++)
ret[i] = i * i;
return ret;
}
constexpr auto sqr = get_sqr();
t.cc: In function 'constexpr std::array<int, 10000> get_sqr()':
t.cc:5:28: error: uninitialized variable 'ret' in 'constexpr' function
5 | std::array<int, 10000> ret;
| ^~~
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug c++/110401] [10/11/12/13/14 Regression] Unhelpful "goto is not a constant expression" in ill-formed pre c++20 constexpr function template
2023-06-25 8:56 [Bug c++/110401] New: Unhelpful "goto is not a constant expression" in ill-formed constexpr function template xry111 at gcc dot gnu.org
@ 2023-06-25 13:15 ` pinskia at gcc dot gnu.org
2023-07-07 10:45 ` [Bug c++/110401] [11/12/13/14 " rguenth at gcc dot gnu.org
` (2 subsequent siblings)
3 siblings, 0 replies; 5+ messages in thread
From: pinskia at gcc dot gnu.org @ 2023-06-25 13:15 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110401
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Summary|Unhelpful "goto is not a |[10/11/12/13/14 Regression]
|constant expression" in |Unhelpful "goto is not a
|ill-formed pre c++20 |constant expression" in
|constexpr function template |ill-formed pre c++20
| |constexpr function template
Last reconfirmed| |2023-06-25
Target Milestone|--- |10.5
Status|UNCONFIRMED |NEW
Known to fail| |7.3.0
Known to work| |7.1.0, 7.2.0
Ever confirmed|0 |1
--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Compiling it with -std=c++11 is even worse as it does not show the reason:
```
<source>:12:36: error: 'constexpr std::array<int, N> get_sqr() [with int N =
10000]' called in a constant expression
12 | constexpr auto sqr = get_sqr<10000>();
| ~~~~~~~~~~~~~~^~
<source>:4:30: note: 'constexpr std::array<int, N> get_sqr() [with int N =
10000]' is not usable as a 'constexpr' function because:
4 | constexpr std::array<int, N> get_sqr()
| ^~~~~~~
```
GCC 7.1 and 7.2 used to have the correct explanation for C++11+:
```
<source>: In instantiation of 'constexpr std::array<int, N> get_sqr() [with int
N = 10000]':
<source>:12:37: required from here
<source>:6:24: error: uninitialized variable 'ret' in 'constexpr' function
std::array<int, N> ret;
^~~
In file included from <source>:1:0:
/opt/compiler-explorer/gcc-7.2.0/include/c++/7.2.0/array:94:12: note: 'struct
std::array<int, 10000>' has no user-provided default constructor
struct array
^~~~~
/opt/compiler-explorer/gcc-7.2.0/include/c++/7.2.0/array:110:56: note: and the
implicitly-defined constructor does not initialize 'int std::array<int,
10000>::_M_elems [10000]'
typename _AT_Type::_Type _M_elems;
^~~~~~~~
<source>:12:37: error: 'constexpr std::array<int, N> get_sqr() [with int N =
10000]' called in a constant expression
constexpr auto sqr = get_sqr<10000>();
^
<source>:4:30: note: 'constexpr std::array<int, N> get_sqr() [with int N =
10000]' is not usable as a constexpr function because:
constexpr std::array<int, N> get_sqr()
^~~~~~~
```
GCC 7.3+ removed the "uninitialized variable 'ret' in 'constexpr' function".
GCC 10+ then removed the 2 notes at the beginning.
Note this is actually valid C++20 so maybe the change in GCC 10 is related to
that ...
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug c++/110401] [11/12/13/14 Regression] Unhelpful "goto is not a constant expression" in ill-formed pre c++20 constexpr function template
2023-06-25 8:56 [Bug c++/110401] New: Unhelpful "goto is not a constant expression" in ill-formed constexpr function template xry111 at gcc dot gnu.org
2023-06-25 13:15 ` [Bug c++/110401] [10/11/12/13/14 Regression] Unhelpful "goto is not a constant expression" in ill-formed pre c++20 " pinskia at gcc dot gnu.org
@ 2023-07-07 10:45 ` rguenth at gcc dot gnu.org
2024-03-22 13:43 ` law at gcc dot gnu.org
2024-07-19 13:20 ` [Bug c++/110401] [12/13/14/15 " rguenth at gcc dot gnu.org
3 siblings, 0 replies; 5+ messages in thread
From: rguenth at gcc dot gnu.org @ 2023-07-07 10:45 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110401
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|10.5 |11.5
--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 10 branch is being closed.
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug c++/110401] [11/12/13/14 Regression] Unhelpful "goto is not a constant expression" in ill-formed pre c++20 constexpr function template
2023-06-25 8:56 [Bug c++/110401] New: Unhelpful "goto is not a constant expression" in ill-formed constexpr function template xry111 at gcc dot gnu.org
2023-06-25 13:15 ` [Bug c++/110401] [10/11/12/13/14 Regression] Unhelpful "goto is not a constant expression" in ill-formed pre c++20 " pinskia at gcc dot gnu.org
2023-07-07 10:45 ` [Bug c++/110401] [11/12/13/14 " rguenth at gcc dot gnu.org
@ 2024-03-22 13:43 ` law at gcc dot gnu.org
2024-07-19 13:20 ` [Bug c++/110401] [12/13/14/15 " rguenth at gcc dot gnu.org
3 siblings, 0 replies; 5+ messages in thread
From: law at gcc dot gnu.org @ 2024-03-22 13:43 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110401
Jeffrey A. Law <law at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |law at gcc dot gnu.org
Priority|P3 |P2
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug c++/110401] [12/13/14/15 Regression] Unhelpful "goto is not a constant expression" in ill-formed pre c++20 constexpr function template
2023-06-25 8:56 [Bug c++/110401] New: Unhelpful "goto is not a constant expression" in ill-formed constexpr function template xry111 at gcc dot gnu.org
` (2 preceding siblings ...)
2024-03-22 13:43 ` law at gcc dot gnu.org
@ 2024-07-19 13:20 ` rguenth at gcc dot gnu.org
3 siblings, 0 replies; 5+ messages in thread
From: rguenth at gcc dot gnu.org @ 2024-07-19 13:20 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110401
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Target Milestone|11.5 |12.5
--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 11 branch is being closed.
^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2024-07-19 13:20 UTC | newest]
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2023-06-25 8:56 [Bug c++/110401] New: Unhelpful "goto is not a constant expression" in ill-formed constexpr function template xry111 at gcc dot gnu.org
2023-06-25 13:15 ` [Bug c++/110401] [10/11/12/13/14 Regression] Unhelpful "goto is not a constant expression" in ill-formed pre c++20 " pinskia at gcc dot gnu.org
2023-07-07 10:45 ` [Bug c++/110401] [11/12/13/14 " rguenth at gcc dot gnu.org
2024-03-22 13:43 ` law at gcc dot gnu.org
2024-07-19 13:20 ` [Bug c++/110401] [12/13/14/15 " rguenth at gcc dot gnu.org
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