[Bug middle-end/61927] [4.9/5 Regression] Wrong results with loop vectorization of: "var[i] = ABS_EXPR<var2[i]> > 9.9e-7"

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61927

--- Comment #6 from Richard Biener <rguenth at gcc dot gnu.org> ---
Hmm, we store

  MEM[(logical(kind=4) *)_227] = vect_patt_319.44_273;
...
  MEM[(logical(kind=4) *)_227 + 4B] = vect_patt_318.52_169;
...
  MEM[(logical(kind=4) *)_227 + 8B] = vect_patt_304.60_132;
...

the result vectors 4 bytes apart but the vectors are 16byte V4SI ones.

So we unroll the inner two loops and get

  for (i = 1; i <= 8; ++i)
    {
      symm_nonzero[i][0][0] = ABS ... > ...;
      ... repeated 9 times with other constant 2nd/3rd index ...
    }

which we vectorize to a loop with two iterations but still 9 vector stores
to symm_nonzero.  This doesn't make much sense...  it looks like SLP
failed half-way.  Or rather the vectorizer is somehow confused by
the bool pattern detected:

t.f90:42:0: note: pattern recognized: VIEW_CONVERT_EXPR<unsigned
int>(symm_nonzero[_200]) = patt_319;

with the VIEW_CONVERT_EXPR on the LHS which is not seen as grouped store.

So it looks like vect_recog_bool_pattern does not handle grouped stores
properly and

Index: tree-vect-patterns.c
===================================================================
--- tree-vect-patterns.c        (revision 218019)
+++ tree-vect-patterns.c        (working copy)
@@ -3261,6 +3261,8 @@ vect_recog_bool_pattern (vec<gimple> *st
       gcc_assert (vectype != NULL_TREE);
       if (!VECTOR_MODE_P (TYPE_MODE (vectype)))
        return NULL;
+      if (STMT_VINFO_GROUP_FIRST_ELEMENT (stmt_vinfo))
+       return NULL;
       if (!check_bool_pattern (var, loop_vinfo, bb_vinfo))
        return NULL;

fixes this testcase (and then does not vectorize this loop).

Any takers making this testcase suitable for the testsuite?  It should
abort() for bogus results and return normally for success.  It should
not output to the terminal.