Re: increase alignment of global structs in increase_alignment pass

[Marek Polacek <polacek at redhat dot com>]

On Tue, Feb 23, 2016 at 09:49:37PM +0530, Prathamesh Kulkarni wrote:

> diff --git a/gcc/tree-vectorizer.c b/gcc/tree-vectorizer.c
> index 2b25b45..a6af535 100644
> --- a/gcc/tree-vectorizer.c
> +++ b/gcc/tree-vectorizer.c
> @@ -794,6 +794,75 @@ make_pass_slp_vectorize (gcc::context *ctxt)
>       This should involve global alignment analysis and in the future also
>       array padding.  */
> 
> +static unsigned get_vec_alignment_for_decl (tree);

Why the forward decl?  Better to topologically sort the functions.

Also, the functions are missing comments.

> +static unsigned
> +get_vec_alignment_for_array_decl (tree array_decl)
> +{
> +  tree type = TREE_TYPE (array_decl);
> +  gcc_assert (TREE_CODE (type) == ARRAY_TYPE);
> +
> +  tree vectype = get_vectype_for_scalar_type (strip_array_types (type));
> +  return (vectype) ? TYPE_ALIGN (vectype) : 0;
> +}
> +
> +static unsigned
> +get_vec_alignment_for_record_decl (tree record_decl)
> +{
> +  tree type = TREE_TYPE (record_decl);
> +  gcc_assert (TREE_CODE (type) == RECORD_TYPE);
> +  unsigned max_align = 0, alignment;
> +  HOST_WIDE_INT offset;
> +
> +  if (DECL_ARTIFICIAL (record_decl) || TYPE_PACKED (type))
> +    return 0;
> +
> +  for (tree field = first_field (type);
> +       field != NULL_TREE;
> +       field = DECL_CHAIN (field))
> +    {
> +      /* C++FE puts node "._0" of code TYPE_DECL. skip that.  */
> +      if (TREE_CODE (field) != FIELD_DECL)
> +	continue;
> +
> +      offset = int_byte_position (field);
> +      alignment = get_vec_alignment_for_decl (field);
> +      if (alignment
> +	  && (offset % (alignment / BITS_PER_UNIT) == 0)
> +	  && (alignment > max_align))
> +	max_align = alignment;
> +    }
> +
> +  return max_align;
> +}
> +
> +static unsigned
> +get_vec_alignment_for_decl (tree decl)
> +{
> +  if (decl == NULL_TREE)
> +    return 0;
> +
> +  gcc_assert (DECL_P (decl));
> +
> +  static unsigned alignment = 0;
> +  tree type = TREE_TYPE (decl);
> +
> +  switch (TREE_CODE (type))
> +    {
> +      case ARRAY_TYPE:
> +	alignment = get_vec_alignment_for_array_decl (decl);
> +	break;
> +      case RECORD_TYPE:
> +	alignment = get_vec_alignment_for_record_decl (decl);
> +	break;
> +      default:
> +	alignment = 0;
> +	break;
> +    }
> +
> +  return (alignment > DECL_ALIGN (decl)) ? alignment : 0;
> +}
> +
>  static unsigned int
>  increase_alignment (void)
>  {
> @@ -804,23 +873,14 @@ increase_alignment (void)
>    /* Increase the alignment of all global arrays for vectorization.  */
>    FOR_EACH_DEFINED_VARIABLE (vnode)
>      {
> -      tree vectype, decl = vnode->decl;
> -      tree t;
> +      tree decl = vnode->decl;
>        unsigned int alignment;
> 
> -      t = TREE_TYPE (decl);
> -      if (TREE_CODE (t) != ARRAY_TYPE)
> -        continue;
> -      vectype = get_vectype_for_scalar_type (strip_array_types (t));
> -      if (!vectype)
> -        continue;
> -      alignment = TYPE_ALIGN (vectype);
> -      if (DECL_ALIGN (decl) >= alignment)
> -        continue;
> +      alignment = get_vec_alignment_for_decl (decl);
> 
> -      if (vect_can_force_dr_alignment_p (decl, alignment))
> +      if (alignment && vect_can_force_dr_alignment_p (decl, alignment))
>          {
> -	  vnode->increase_alignment (TYPE_ALIGN (vectype));
> +	  vnode->increase_alignment (alignment);
>            dump_printf (MSG_NOTE, "Increasing alignment of decl: ");
>            dump_generic_expr (MSG_NOTE, TDF_SLIM, decl);
>            dump_printf (MSG_NOTE, "\n");


	Marek