[Bug middle-end/57748] [4.8/4.9 Regression] ICE when expanding assignment to unaligned zero-sized array

["bernd.edlinger at hotmail dot de" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=57748

--- Comment #26 from Bernd Edlinger <bernd.edlinger at hotmail dot de> ---
(In reply to Richard Biener from comment #25)
> I think that
> 
>       tem = get_inner_reference (to, &bitsize, &bitpos, &offset, &mode1,
>                                  &unsignedp, &volatilep, true);
> 
>       if (TREE_CODE (to) == COMPONENT_REF
>           && DECL_BIT_FIELD_TYPE (TREE_OPERAND (to, 1)))
>         get_bit_range (&bitregion_start, &bitregion_end, to, &bitpos,
> &offset);
> 
>       /* If we are going to use store_bit_field and extract_bit_field,
>          make sure to_rtx will be safe for multiple use.  */
>       mode = TYPE_MODE (TREE_TYPE (tem));
>       if (TREE_CODE (tem) == MEM_REF
>           && mode != BLKmode
>           && ((align = get_object_alignment (tem))
>               < GET_MODE_ALIGNMENT (mode))
>           && ((icode = optab_handler (movmisalign_optab, mode))
>               != CODE_FOR_nothing))
> 
> is overly pessimistic.  What matters is the mode of the access, not that
> of the access base object!
> 
> Which means the pre-handling of
> 
>   /* Handle misaligned stores.  */
>   mode = TYPE_MODE (TREE_TYPE (to));
>   if ((TREE_CODE (to) == MEM_REF
>        || TREE_CODE (to) == TARGET_MEM_REF)
>       && mode != BLKmode
>       && !mem_ref_refers_to_non_mem_p (to)
> 
> should be made to trigger for all 'to', not just bare MEM_REF/TARGET_MEM_REF.
> Then the other movmisalign path can be completely removed.

struct s
{
  int x:19;
} __attribute__((packed));
int foo(struct s *s)
{
  s->x=1;
}

in this case of a packed field the TREE_CODE (to) will be COMPONENT_REF
TYPE_MODE (TREE_TYPE (to)) will be SImode.
If this would go to the pre-handling, this will not work for packed bit-fields.

this handling is just for: int *x;

*x = 1;

or: struct s *x, *y;

*x = *y; //if struct s is not BLKmode.