[Bug tree-optimization/67800] New: [6 Regression] Missed vectorization opportunity on x86

["afomin.mailbox at gmail dot com" <gcc-bugzilla at gcc dot gnu dot org>]

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

            Bug ID: 67800
           Summary: [6 Regression] Missed vectorization opportunity on x86
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: afomin.mailbox at gmail dot com
                CC: izamyatin at gmail dot com, rguenth at gcc dot gnu.org,
                    ysrumyan at gmail dot com
  Target Milestone: ---
            Target: i686-*-*

Created attachment 36434
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=36434&action=edit
A reproducer

A loop in the test attached compiled with -m32 -msse4.2 -O2 -ftree-vectorize
-fPIE -pie -c is no more vectorized after r223525 (while on r223524 everything
is OK) because of strange DOT_PROD_EXPR recognition (see below).

vect_is_simple_use: operand _15
def_stmt: _15 = _14 * 76;
type of def: internal
vect_recog_dot_prod_pattern: detected: patt_47 = DOT_PROD_EXPR <_2, 76, _17>;
pattern recognized: patt_47 = DOT_PROD_EXPR <_2, 76, _17>;