Should ADJUST_FIELD_ALIGN honor __attribute__((packed))?

[Daniel Jacobowitz <drow at false dot org>]

Right now, if a target does not use MIN (myalign, computed) in every branch
of its ADJUST_FIELD_ALIGN, __attribute__((packed)) won't work right.  For
instance, in rs6000/sysv4.h:

/* An expression for the alignment of a structure field FIELD if the
   alignment computed in the usual way is COMPUTED.  */
#define ADJUST_FIELD_ALIGN(FIELD, COMPUTED) \
        ((TARGET_ALTIVEC && TREE_CODE (TREE_TYPE (FIELD)) == VECTOR_TYPE) \
         ? 128 : COMPUTED)

This means that given the types (excuse my syntax, I haven't used AltiVec):
struct S1 {
  char f;
  int vec __attribute__((vector_size(16)));
};

struct S2 {
  char f;
  int vec __attribute__((vector_size(16)));
} __attribute__((packed));

struct S3 {
  char f;
  int vec __attribute__((vector_size(16),aligned(1)));
} __attribute__((packed));

structures S1 and S2 will have the same size, which hardly seems right.
Structure S3 will have a different size.

I suspect we should either fix all the copies of ADJUST_FIELD_ALIGN, or
guard calls with !DECL_PACKED.  I'm not sure which.  Any opinions?

-- 
Daniel Jacobowitz
MontaVista Software                         Debian GNU/Linux Developer