[Bug tree-optimization/97352] New: gcc.dg/vect/bb-slp-pr78205.c fails to vectorize all opportunities with AVX

["rguenth at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97352

            Bug ID: 97352
           Summary: gcc.dg/vect/bb-slp-pr78205.c fails to vectorize all
                    opportunities with AVX
           Product: gcc
           Version: 11.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rguenth at gcc dot gnu.org
  Target Milestone: ---

When using AVX vectors

double x[2], a[4], b[4], c[5];

void foo ()
{
  a[0] = c[0];
  a[1] = c[1];
  a[2] = c[0];
  a[3] = c[1];
  b[0] = c[2];
  b[1] = c[3];
  b[2] = c[2];
  b[3] = c[3];
  x[0] = c[4];
  x[1] = c[4];
}

only vectorizes the x[] stores since the overall SLP analysis succeeds with
V4DFmode but only parts of the opportunities are finally vectorized and thus
SLP vectorization with V2DFmode isn't even tried.

This is the issue that vector mode iteration works on wrong granularity.

/home/rguenther/src/gcc3/gcc/testsuite/gcc.dg/vect/bb-slp-pr78205.c:17:8: note:
  === vect_slp_analyze_instance_dependence ===
/home/rguenther/src/gcc3/gcc/testsuite/gcc.dg/vect/bb-slp-pr78205.c:9:8: note: 
 === vect_slp_analyze_instance_alignment ===
/home/rguenther/src/gcc3/gcc/testsuite/gcc.dg/vect/bb-slp-pr78205.c:9:8: note: 
removing SLP instance operations starting from: a[0] = _1;
/home/rguenther/src/gcc3/gcc/testsuite/gcc.dg/vect/bb-slp-pr78205.c:13:8: note:
  === vect_slp_analyze_instance_alignment ===
/home/rguenther/src/gcc3/gcc/testsuite/gcc.dg/vect/bb-slp-pr78205.c:13:8: note:
 removing SLP instance operations starting from: b[0] = _3;
/home/rguenther/src/gcc3/gcc/testsuite/gcc.dg/vect/bb-slp-pr78205.c:13:8: note:
  === vect_slp_analyze_operations ===

and the failure is because of the now late performed

/* Analyze alignment of DRs of stmts in NODE.  */

static bool
vect_slp_analyze_node_alignment (vec_info *vinfo, slp_tree node)
{
...
  /* We need to commit to a vector type for the group now.  */
  if (is_a <bb_vec_info> (vinfo)
      && !vect_update_shared_vectype (first_stmt_info, SLP_TREE_VECTYPE
(node)))
    return false;

because the other SLP instance (with x[] stores) set the vector type to V2DF
while this one wants V4DF.