[Bug tree-optimization/67800] [6 Regression] Missed vectorization opportunity on x86 (DOT_PROD_EXPR in non-reduction)

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67800

--- Comment #7 from Richard Biener <rguenth at gcc dot gnu.org> ---
Ah, so reverting these changes causes

FAIL: gcc.dg/vect/slp-reduc-sad.c scan-tree-dump vect "vectorizing stmts using
SLP"
FAIL: gcc.dg/vect/slp-reduc-sad.c scan-tree-dump-times vect "vectorized 1
loops" 1

with similar testcases using a dot product or widening sum pattern would
need to be added.  Note that the above are in reduction context but only
the first stmt of the reduction chain is marked as such.

Thus we need to amend the check with ! STMT_VINFO_GROUP_FIRST_ELEMENT
(stmt_vinfo).

Testing that now.