[Bug c++/125341] New: alignas must not ultimately lower the alignment

[aoliva at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=125341

            Bug ID: 125341
           Summary: alignas must not ultimately lower the alignment
           Product: gcc
           Version: 17.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: aoliva at gcc dot gnu.org
  Target Milestone: ---

// { dg-do compile }

static_assert(alignof(long long)>alignof(char)); alignas(char) long long x; //
{ dg-error "static_assert|lowering alignment" }

void f() {
  static_assert(alignof(long long)>alignof(char)); alignas(char) long long x;
// { dg-error "static_assert|lowering alignment" }
}

[dcl.align]/5 (in C++11; with clarifying wording changes in C++23) says:
The combined effect of all alignment-specifiers in a declaration shall not
specify an alignment that is less strict than the alignment that would be
required for the entity being declared if all alignment-specifiers were omitted
(including those in other declarations).