[Bug c++/90847] New: requested alignment is not an integer constant

[zhonghao at pku dot org.cn]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90847

            Bug ID: 90847
           Summary: requested alignment is not an integer constant
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: zhonghao at pku dot org.cn
  Target Milestone: ---

My gcc is 10.0.0, and the code is:

template <int N> 
void test() {
 constexpr int N2 = N;
 typedef int T alignas(N2);
 // error: requested alignment is not an integer constant
}

int main() {
 test<4>();
 return 0;
}

gcc accepts the code. clang rejects it:
source>:4:16: error: 'alignas' attribute only applies to variables, data
members and tag types

 typedef int T alignas(N2);

               ^

1 error generated.

Compiler returned: 1

icc gives a warning:
<source>(4): warning #3463: alignas does not apply here

   typedef int T alignas(N2);

                 ^

Compiler returned: 0