[Bug middle-end/87524] New: inconsistent handling of attribute aligned between types and variables

[msebor at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87524

            Bug ID: 87524
           Summary: inconsistent handling of attribute aligned between
                    types and variables
           Product: gcc
           Version: 9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: msebor at gcc dot gnu.org
  Target Milestone: ---

When multiple instances of attribute aligned are applied to the declaration of
a variable the most restrictive instance wins.

But when multiple instances of attribute aligned are applied to the definition
of a type it's the last one that wins.

The attribute should have the same effect on all entities it applies to, i.e.,
functions, types, and variables.


$ cat x.c && gcc -S -Wall -fdump-tree-optimized=/dev/stdout x.c
#define A(N) __attribute__ ((aligned (N)))

void f0 (void)
{
  A (2) A(4) char c4;
  _Static_assert (_Alignof (c4) == 4, "_Alignof (c4) == 4");
}

void g0 (void)
{
  A (4) A (2) char c4;
  _Static_assert (_Alignof (c4) == 4, "_Alignof (c4) == 4");
}


void f1 (void)
{
  typedef A (2) A (4) char C4;
  _Static_assert (_Alignof (C4) == 4, "_Alignof (C4) == 4");
}

void g1 (void)
{
  typedef A (4) A (2) char C4;
  _Static_assert (_Alignof (C4) == 4, "_Alignof (C4) == 4");
}
x.c: In function ‘g1’:
x.c:25:3: error: static assertion failed: "_Alignof (C4) == 4"
25 |   _Static_assert (_Alignof (C4) == 4, "_Alignof (C4) == 4");
   |   ^~~~~~~~~~~~~~