Re: [PATCH, PR 55334] Disable IPA-CP on restrict pointers to arrays

[Richard Biener <richard dot guenther at gmail dot com>]

On Mon, Feb 18, 2013 at 9:06 PM, Martin Jambor <mjambor@suse.cz> wrote:
> Hi,
>
> after much pondering about PR 55334 I came to conclusion that no nice
> fix to the regression could be introduced in stage4.  So for the sake
> of the SPEC 200 benchmark I decided to cripple IPA-CP on restrict
> pointers to arrays so that the restrict-ness of the memory references
> which need to be vectorized is not lost.
>
> I have tried various less aggressive tricks like only propagating the
> one constant address that heuristics decided was profitable and not
> all the others that came from the same calling contexts (and were
> restrict) but then inlining came along and finished the deed with the
> same consequences as IPA-CP had.
>
> That only reinforced my feeling that the patch below is a spec hack
> and that we ought to find a better way of preserving the restrict-ness
> across IPA optimizations.  Therefore I will keep the bug open and
> revert this patch after 4.8 is branched and stage1 opens.
>
> Meanwhile, this passes bootstrap and testsuite on x86_64-linux.  OK
> for trunk?
>
> Thanks,
>
> Martin
>
>
> 2013-02-07  Martin Jambor  <mjambor@suse.cz>
>
>         PR tree-optimization/55334
>         * ipa-cp.c (initialize_node_lattices): Disable IPA-CP through and to
>         restricted pointers to arrays.
>
> Index: src/gcc/ipa-cp.c
> ===================================================================
> --- src.orig/gcc/ipa-cp.c
> +++ src/gcc/ipa-cp.c
> @@ -730,6 +730,22 @@ initialize_node_lattices (struct cgraph_
>                  cgraph_node_name (node), node->uid,
>                  disable ? "BOTTOM" : "VARIABLE");
>      }
> +  if (!disable)
> +    for (i = 0; i < ipa_get_param_count (info) ; i++)
> +      {
> +       struct ipcp_param_lattices *plats = ipa_get_parm_lattices (info, i);
> +       tree t = TREE_TYPE (ipa_get_param(info, i));
> +
> +       if (TYPE_RESTRICT (t) && POINTER_TYPE_P (t)

You want to first test for POINTER_TYPE_P and then for TYPE_RESTRICT.

> +           && TREE_CODE (TREE_TYPE (t)) == ARRAY_TYPE)

With only testing for ARRAY_TYPE here you will still IPA-CP array
descriptors, right?  Those are RECORD_TYPE, the parameter being
DECL_BY_REFERENCE.  So I'd try instead

                && DECL_BY_REFERENCE (ipa_get_parm (info, i))

which leads me to the question - what is ipa_get_parm (info, i) returning?
Is it the lattice _value_?  Or is it the PARM_DECL of the callee (which is
the only important piece of information!)?

Thanks,
Richard.

> +         {
> +           set_lattice_to_bottom (&plats->itself);
> +           if (dump_file && (dump_flags & TDF_DETAILS)
> +               && !node->alias && !node->thunk.thunk_p)
> +             fprintf (dump_file, "Going to ignore param %i of of %s/%i.\n",
> +                      i, cgraph_node_name (node), node->uid);
> +         }
> +      }
>
>    for (ie = node->indirect_calls; ie; ie = ie->next_callee)
>      if (ie->indirect_info->polymorphic)
>