[Bug c++/79024] New: alignas / alignof report wrong alignment for 64bit integer types for 32bit target

[gnu-9fbaow at upsuper dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79024

            Bug ID: 79024
           Summary: alignas / alignof report wrong alignment for 64bit
                    integer types for 32bit target
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gnu-9fbaow at upsuper dot org
  Target Milestone: ---

See the following code:

#include <cstddef>
#include <cstdint>
struct Test1 { char c; uint64_t u; };
struct Test2 { char c; alignas(uint64_t) uint64_t u; };
static_assert(sizeof(Test1) == sizeof(Test2), "Size should be same, no?");
static_assert(offsetof(Test1, u) == offsetof(Test2, u),
              "Offset should be same, no?");

Compiling this code with "g++ -m32", both static assertions are broken, which
indicates that uint64_t in Test1 is not aligned as what alignas reports.

FWIW, MSVC doesn't have this issue but clang has exactly the same issue.