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From: "crazylht at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/107082] New: Fix incorrect handle in
 vectorizable_induction for mixed induction type
Date: Thu, 29 Sep 2022 07:22:36 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D107082

            Bug ID: 107082
           Summary: Fix incorrect handle in vectorizable_induction for
                    mixed induction type
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: crazylht at gmail dot com
  Target Milestone: ---

The codes in vectorizable_induction for slp_node assume all phi_info
have same induction type(vect_step_op_add), but since we support
nonlinear induction, it could be wrong handled.

https://gcc.gnu.org/pipermail/gcc-patches/2022-September/601913.html

----------Comments from Richard-------
While it works to check this here the canonical place to match up def
types is in
vect_get_and_check_slp_defs.  There we do

      /* Not first stmt of the group, check that the def-stmt/s match
         the def-stmt/s of the first stmt.  Allow different definition
         types for reduction chains: the first stmt must be a
         vect_reduction_def (a phi node), and the rest
         end in the reduction chain.  */
      if ((!vect_def_types_match (oprnd_info->first_dt, dt)
           && !(oprnd_info->first_dt =3D=3D vect_reduction_def
                && !STMT_VINFO_DATA_REF (stmt_info)

the induction def type match now needs to also compare
STMT_VINFO_LOOP_PHI_EVOLUTION_TYPE
it seems.

Note we also fail to do this for STMT_VINFO_REDUC_TYPE (but that's eventual=
ly
only computed too late).

Being able to reject this during SLP discovery means that if you'd have

   x =3D i + j;
   y =3D j + i;

with two different induction types for 'i' and 'j', SLP discovery can
try commutative
swapping to match the inductions up for x and y and successfully SLP
the operation.

That said, I can see the checking condition becoming more ugly (please don't
try to amend vect_def_types_match itself), adding something like

    || (oprnd_info->first_dt =3D=3D vect_induction_def
        && STMT_VINFO_LOOP_PHI_EVOLUTION_TYPE (...) !=3D ... (stmts[0]))

Can you try doing that?
-----comments end--------


Open this PR to track this.=