[Bug middle-end/95309] New: [11 Regression] Many targets failing ssa-dom-cse-2.c after vectorizer changes

[law at redhat dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95309

            Bug ID: 95309
           Summary: [11 Regression] Many targets failing ssa-dom-cse-2.c
                    after vectorizer changes
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: law at redhat dot com
  Target Milestone: ---

Various ports have regressed the tree-ssa/ssa-dom-cse-2.c after this change:

commit a4b48fc47c3406b6f41be093c4615879b7006710
Author: Richard Biener <rguent...@suse.de>
Date:   Mon May 18 16:05:00 2020 +0200

    cost invariant nodes from vect_slp_analyze_node_operations SLP walk

    2020-05-19  Richard Biener  <rguent...@suse.de>

            * tree-vectorizer.h (_slp_tree::vectype): Add field.
            (SLP_TREE_VECTYPE): New.
            * tree-vect-slp.c (vect_create_new_slp_node): Initialize
            SLP_TREE_VECTYPE.
            (vect_create_new_slp_node): Likewise.
            (vect_prologue_cost_for_slp): Move here from tree-vect-stmts.c
            and simplify.
            (vect_slp_analyze_node_operations): Walk nodes children for
            invariant costing.
            (vect_get_constant_vectors): Use local scope op variable.
            * tree-vect-stmts.c (vect_prologue_cost_for_slp_op): Remove here.
            (vect_model_simple_cost): Adjust.
            (vect_model_store_cost): Likewise.
            (vectorizable_store): Likewise.

You should be able to see this on the iq2000-elf port (and many others).

I believe the test is supposed to verify that we're able to determine the
return
value statically after unrolling the loop.  It's unclear if the stores get in
the
way of cse-ing the assignment to _22 and _29 in the dump or if there's
something
else going on:

  MEM[(int *)&a] = { 0 };
  MEM[(int *)&a + 4B] = { 1 };
  MEM[(int *)&a + 8B] = { 2 };
  MEM[(int *)&a + 12B] = { 3 };
  MEM[(int *)&a + 16B] = { 4 };
  MEM[(int *)&a + 20B] = { 5 };
  MEM[(int *)&a + 24B] = { 6 };
  MEM[(int *)&a + 28B] = { 7 };
  _22 = a[0];
  _29 = a[1];
  sum_30 = _22 + _29;
  _36 = a[2];
  sum_37 = sum_30 + _36;
  _43 = a[3];
  sum_44 = sum_37 + _43;
  _50 = a[4];
  sum_51 = sum_44 + _50;
  _57 = a[5];
  sum_58 = sum_51 + _57;
  _64 = a[6];
  sum_65 = sum_58 + _64;
  _1 = a[7];
  sum_16 = _1 + sum_65;
  a ={v} {CLOBBER};
  return sum_16;