Re: [PATCH] data-ref: Improve non-loop disambiguation [PR106019]

[Richard Biener <rguenther@suse.de>]

> Am 21.06.2022 um 17:16 schrieb Richard Sandiford via Gcc-patches <gcc-patches@gcc.gnu.org>:
> 
> When dr_may_alias_p is called without a loop context, it tries
> to use the tree-affine interface to calculate the difference
> between the two addresses and use that difference to check whether
> the gap between the accesses is known at compile time.  However, as the
> example in the PR shows, this doesn't expand SSA_NAMEs and so can easily
> be defeated by things like reassociation.
> 
> One fix would have been to use aff_combination_expand to expand the
> SSA_NAMEs, but we'd then need some way of maintaining the associated
> cache.  This patch instead reuses the innermost_loop_behavior fields
> (which exist even when no loop context is provided).
> 
> It might still be useful to do the aff_combination_expand thing too,
> if an example turns out to need it.
> 
> Tested on aarch64-linux-gnu and x86_64-linux-gnu.  OK to install?
> 

Ok.

Thanks,
Richard 

> Richard
> 
> 
> gcc/
>    PR tree-optimization/106019
>    * tree-data-ref.cc (dr_may_alias_p): Try using the
>    innermost_loop_behavior to disambiguate non-loop queries.
> 
> gcc/testsuite/
>    PR tree-optimization/106019
>    * gcc.dg/vect/bb-slp-pr106019.c: New test.
> ---
> gcc/testsuite/gcc.dg/vect/bb-slp-pr106019.c | 15 +++++++++++++++
> gcc/tree-data-ref.cc                        | 19 +++++++++++++++++++
> 2 files changed, 34 insertions(+)
> create mode 100644 gcc/testsuite/gcc.dg/vect/bb-slp-pr106019.c
> 
> diff --git a/gcc/testsuite/gcc.dg/vect/bb-slp-pr106019.c b/gcc/testsuite/gcc.dg/vect/bb-slp-pr106019.c
> new file mode 100644
> index 00000000000..218d7cca33d
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/vect/bb-slp-pr106019.c
> @@ -0,0 +1,15 @@
> +/* { dg-do compile } */
> +
> +void f(double *p, long i)
> +{
> +    p[i+0] += 1;
> +    p[i+1] += 1;
> +}
> +void g(double *p, long i)
> +{
> +    double *q = p + i;
> +    q[0] += 1;
> +    q[1] += 1;
> +}
> +
> +/* { dg-final { scan-tree-dump-not "can't determine dependence" slp2 } } */
> diff --git a/gcc/tree-data-ref.cc b/gcc/tree-data-ref.cc
> index 8b7edf2124a..90242948c27 100644
> --- a/gcc/tree-data-ref.cc
> +++ b/gcc/tree-data-ref.cc
> @@ -2968,6 +2968,25 @@ dr_may_alias_p (const struct data_reference *a, const struct data_reference *b,
>      disambiguation.  */
>   if (!loop_nest)
>     {
> +      tree tree_size_a = TYPE_SIZE_UNIT (TREE_TYPE (DR_REF (a)));
> +      tree tree_size_b = TYPE_SIZE_UNIT (TREE_TYPE (DR_REF (b)));
> +
> +      if (DR_BASE_ADDRESS (a)
> +      && DR_BASE_ADDRESS (b)
> +      && operand_equal_p (DR_BASE_ADDRESS (a), DR_BASE_ADDRESS (b))
> +      && operand_equal_p (DR_OFFSET (a), DR_OFFSET (b))
> +      && poly_int_tree_p (tree_size_a)
> +      && poly_int_tree_p (tree_size_b)
> +      && !ranges_maybe_overlap_p (wi::to_widest (DR_INIT (a)),
> +                      wi::to_widest (tree_size_a),
> +                      wi::to_widest (DR_INIT (b)),
> +                      wi::to_widest (tree_size_b)))
> +    {
> +      gcc_assert (integer_zerop (DR_STEP (a))
> +              && integer_zerop (DR_STEP (b)));
> +      return false;
> +    }
> +
>       aff_tree off1, off2;
>       poly_widest_int size1, size2;
>       get_inner_reference_aff (DR_REF (a), &off1, &size1);
> -- 
> 2.25.1
>