Alignas broken when used with constexpr array data member for structure

[Mason]

On 09/01/2018 14:39, Alec Teal wrote:

> In GCC 4.8.4 I have something like the following:

FWIW, 4.8 is no longer supported (2013)

> constexpr int x = 5;
> constexpr int y = 4;
> struct alignas(y) my_data_block {
>     char data[x];
> };
> 
> 
> And it causes some weird errors to the tune of "size of array 'data' is
> not an integral constant-expression" in the presence of the alignas

A good support request should specify
- exact compiler version (GCC 4.8.4)
- a small testcase (given above)
- exact compilation flags (missing)
- exact error message


Compiling the above source on godbolt using:
gcc 4.8.4 -Wall -Wextra

1 : <source>:1:1: warning: identifier 'constexpr' is a keyword in C++11 [-Wc++0x-compat]
 constexpr int x = 5;
 ^
1 : <source>:1:1: error: 'constexpr' does not name a type
1 : <source>:1:1: note: C++11 'constexpr' only available with -std=c++11 or -std=gnu++11
2 : <source>:2:1: error: 'constexpr' does not name a type
 constexpr int y = 4;
 ^
2 : <source>:2:1: note: C++11 'constexpr' only available with -std=c++11 or -std=gnu++11
3 : <source>:3:19: error: expected initializer before 'my_data_block'
 struct alignas(y) my_data_block {
                   ^
Compiler returned: 1



Compiling the above source on godbolt using:
gcc 4.8.4 -Wall -Wextra -std=c++11

No errors.


So it seems I can't reproduce the issue?

Looking at Bugzilla as jwakely suggested turns up
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58601
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70124


Regards.