This is the mail archive of the gcc@gcc.gnu.org mailing list for the GCC project.


Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]
Other format: [Raw text]

Re: increase alignment of global structs in increase_alignment pass


On 19 May 2016 at 13:19, Richard Biener <rguenther@suse.de> wrote:
> On Thu, 19 May 2016, Prathamesh Kulkarni wrote:
>
>> On 18 May 2016 at 19:38, Richard Biener <rguenther@suse.de> wrote:
>> > On Wed, 18 May 2016, Prathamesh Kulkarni wrote:
>> >
>> >> On 17 May 2016 at 18:36, Richard Biener <rguenther@suse.de> wrote:
>> >> > On Wed, 11 May 2016, Prathamesh Kulkarni wrote:
>> >> >
>> >> >> On 6 May 2016 at 17:20, Richard Biener <rguenther@suse.de> wrote:
>> >> >> >
>> >> >> > You can't simply use
>> >> >> >
>> >> >> > +      offset = int_byte_position (field);
>> >> >> >
>> >> >> > as it can be placed at variable offset which will make int_byte_position
>> >> >> > ICE.  Note it also returns a truncated byte position (bit position
>> >> >> > stripped) which may be undesirable here.  I think you want to use
>> >> >> > bit_position and if and only if DECL_FIELD_OFFSET and
>> >> >> > DECL_FIELD_BIT_OFFSET are INTEGER_CST.
>> >> >> oops, I didn't realize offsets could be variable.
>> >> >> Will that be the case only for VLA member inside struct ?
>> >> >
>> >> > And non-VLA members after such member.
>> >> >
>> >> >> > Your observation about the expensiveness of the walk still stands I guess
>> >> >> > and eventually you should at least cache the
>> >> >> > get_vec_alignment_for_record_decl cases.  Please make those workers
>> >> >> > _type rather than _decl helpers.
>> >> >> Done
>> >> >> >
>> >> >> > You seem to simply get at the maximum vectorized field/array element
>> >> >> > alignment possible for all arrays - you could restrict that to
>> >> >> > arrays with at least vector size (as followup).
>> >> >> Um sorry, I didn't understand this part.
>> >> >
>> >> > It doesn't make sense to align
>> >> >
>> >> > struct { int a; int b; int c; int d; float b[3]; int e; };
>> >> >
>> >> > because we have a float[3] member.  There is no vector size that
>> >> > would cover the float[3] array.
>> >> Thanks for the explanation.
>> >> So we do not want to align struct if sizeof (array_field) < sizeof
>> >> (vector_type).
>> >> This issue is also present without patch for global arrays, so I modified
>> >> get_vec_alignment_for_array_type, to return 0 if sizeof (array_type) <
>> >> sizeof (vectype).
>> >> >
>> >> >> >
>> >> >> > +  /* Skip artificial decls like typeinfo decls or if
>> >> >> > +     record is packed.  */
>> >> >> > +  if (DECL_ARTIFICIAL (record_decl) || TYPE_PACKED (type))
>> >> >> > +    return 0;
>> >> >> >
>> >> >> > I think we should honor DECL_USER_ALIGN as well and not mess with those
>> >> >> > decls.
>> >> >> Done
>> >> >> >
>> >> >> > Given the patch now does quite some extra work it might make sense
>> >> >> > to split the symtab part out of the vect_can_force_dr_alignment_p
>> >> >> > predicate and call that early.
>> >> >> In the patch I call symtab_node::can_increase_alignment_p early. I tried
>> >> >> moving that to it's callers - vect_compute_data_ref_alignment and
>> >> >> increase_alignment::execute, however that failed some tests in vect, and
>> >> >> hence I didn't add the following hunk in the patch. Did I miss some
>> >> >> check ?
>> >> >
>> >> > Not sure.
>> >> >
>> >> >> diff --git a/gcc/tree-vect-data-refs.c b/gcc/tree-vect-data-refs.c
>> >> >> index 7652e21..2c1acee 100644
>> >> >> --- a/gcc/tree-vect-data-refs.c
>> >> >> +++ b/gcc/tree-vect-data-refs.c
>> >> >> @@ -795,7 +795,10 @@ vect_compute_data_ref_alignment (struct data_reference *dr)
>> >> >>    && TREE_CODE (TREE_OPERAND (base, 0)) == ADDR_EXPR)
>> >> >>   base = TREE_OPERAND (TREE_OPERAND (base, 0), 0);
>> >> >>
>> >> >> -      if (!vect_can_force_dr_alignment_p (base, TYPE_ALIGN (vectype)))
>> >> >> +      if (!(TREE_CODE (base) == VAR_DECL
>> >> >> +            && decl_in_symtab_p (base)
>> >> >> +            && symtab_node::get (base)->can_increase_alignment_p ()
>> >> >> +            && vect_can_force_dr_alignment_p (base, TYPE_ALIGN (vectype))))
>> >> >>   {
>> >> >>    if (dump_enabled_p ())
>> >> >>      {
>> >> >
>> >> > +  for (tree field = first_field (type);
>> >> > +       field != NULL_TREE;
>> >> > +       field = DECL_CHAIN (field))
>> >> > +    {
>> >> > +      /* Skip if not FIELD_DECL or has variable offset.  */
>> >> > +      if (TREE_CODE (field) != FIELD_DECL
>> >> > +         || TREE_CODE (DECL_FIELD_OFFSET (field)) != INTEGER_CST
>> >> > +         || TREE_CODE (DECL_FIELD_BIT_OFFSET (field)) != INTEGER_CST
>> >> > +         || DECL_USER_ALIGN (field)
>> >> > +         || DECL_ARTIFICIAL (field))
>> >> > +       continue;
>> >> >
>> >> > you can stop processing the type and return 0 here if the offset
>> >> > is not an INTEGER_CST.  All following fields will have the same issue.
>> >> >
>> >> > +      /* FIXME: is this check necessary since we check for variable
>> >> > offset above ?  */
>> >> > +      if (TREE_CODE (offset_tree) != INTEGER_CST)
>> >> > +       continue;
>> >> >
>> >> > the check should not be necessary.
>> >> >
>> >> >       offset = tree_to_uhwi (offset_tree);
>> >> >
>> >> > but in theory offset_tree might not fit a unsigned HOST_WIDE_INT, so
>> >> > instead of for INTEGER_CST please check ! tree_fits_uhwi_p (offset_tree).
>> >> > As above all following fields will also fail the check if this fails so
>> >> > you can return 0 early.
>> >> >
>> >> > +static unsigned
>> >> > +get_vec_alignment_for_type (tree type)
>> >> > +{
>> >> > +  if (type == NULL_TREE)
>> >> > +    return 0;
>> >> > +
>> >> > +  gcc_assert (TYPE_P (type));
>> >> > +
>> >> > +  unsigned *slot = type_align_map->get (type);
>> >> > +  if (slot)
>> >> > +    return *slot;
>> >> >
>> >> > I suggest to apply the caching only for the RECORD_TYPE case to keep
>> >> > the size of the map low.
>> >> >
>> >> > Otherwise the patch looks ok now.
>> >> I have done the suggested changes in attached patch.
>> >> Is this version OK to commit after bootstrap+test ?
>> >> The patch survives cross-testing on arm*-*-* and aarch64*-*-*.
>> >
>> > +  tree type_size_tree = TYPE_SIZE (type);
>> > +  if (!type_size_tree)
>> > +    return TYPE_ALIGN (vectype);
>> > +
>> > +  if (TREE_CODE (type_size_tree) != INTEGER_CST)
>> > +    return TYPE_ALIGN (vectype);
>> > +
>> > +  /* If array has constant size, ensure that it's at least equal to
>> > +     size of vector type.  */
>> > +  if (!tree_fits_uhwi_p (type_size_tree))
>> > +    return TYPE_ALIGN (vectype);
>> > +  unsigned HOST_WIDE_INT type_size = tree_to_uhwi (type_size_tree);
>> > +
>> > +  tree vectype_size_tree = TYPE_SIZE (vectype);
>> > +  if (!tree_fits_uhwi_p (vectype_size_tree))
>> > +    return TYPE_ALIGN (vectype);
>> > +
>> > +  unsigned HOST_WIDE_INT vectype_size = tree_to_uhwi (vectype_size_tree);
>> > +  return (type_size > vectype_size) ? TYPE_ALIGN (vectype) : 0;
>> >
>> > please change this to
>> >
>> >   if (! TYPE_SIZE (type)
>> >       || TREE_CODE (TYPE_SIZE (type)) != INTEGER_CST
>> >       || tree_int_cst_lt (TYPE_SIZE (type), TYPE_SIZE (vectype)))
>> >     return 0;
>> >
>> >   return TYPE_ALIGN (vectype);
>> >
>> > consistent with the handling for "VLA" records.
>> >
>> > +  unsigned *slot = type_align_map->get (type);
>> > +  if (slot)
>> > +    return *slot;
>> > +
>> > +  unsigned max_align = 0, alignment;
>> > +  HOST_WIDE_INT offset;
>> > +  tree offset_tree;
>> > +
>> > +  if (TYPE_PACKED (type))
>> > +    return 0;
>> > +
>> >
>> > move the tye_align_map query after the TYPE_PACKED check.
>> >
>> > +      /* We don't need to process the type further if offset is variable,
>> > +        since the offsets of remaining members will also be variable.  */
>> > +      if (TREE_CODE (DECL_FIELD_OFFSET (field)) != INTEGER_CST
>> > +         || TREE_CODE (DECL_FIELD_BIT_OFFSET (field)) != INTEGER_CST)
>> > +       return 0;
>> >
>> > just break; here (and in the other case returning zero).  If a
>> > previous record field said we'd want to align we still should align.
>> > Also we want to store 0 into the type_align_map as well.
>> >
>> > Ok with those changes.
>> Hi,
>> Is this version OK ?
>> Cross tested on arm*-*-* and aarch64*-*-*
>
> Yes.  Btw, please always do a regular bootstrap and regtest, cross-testing
> alone is _not_ sufficient!
Thanks, bootstrapped and tested on aarch64-linux-gnu, ppc64le-linux-gnu.
Unfortunately I screwed up while committing (added the patch but not
the test-cases :/).
Patch committed in r236502, test-cases committed in r236503.

Thanks,
Prathamesh
>
> Thanks,
> Richard.
>
>> Thanks,
>> Prathamesh
>> >
>> > Thanks,
>> > Richard.
>>
>
> --
> Richard Biener <rguenther@suse.de>
> SUSE LINUX GmbH, GF: Felix Imendoerffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nuernberg)

Attachment: patch-4.diff
Description: Text document

2016-05-19  Prathamesh Kulkarni  <prathamesh.kulkarni@linaro.org>

	* tree-vectorizer.c (get_vec_alignment_for_decl): New static function.
	(get_vec_alignment_for_array_decl): Likewise.
	(get_vec_alignment_for_record_decl): Likewise.
	(increase_alignment::execute): Move code to find alignment to
	get_vec_alignment_for_array_decl and call get_vec_alignment_for_decl.
	(type_align_map): New hash_map.

testsuite/
	* gcc.dg/vect/section-anchors-vect-70.c: New test-case.
	* gcc.dg/vect/section-anchors-vect-71.c: Likewise.
	* gcc.dg/vect/section-anchors-vect-72.c: Likewise.

Index Nav: [Date Index] [Subject Index] [Author Index] [Thread Index]
Message Nav: [Date Prev] [Date Next] [Thread Prev] [Thread Next]