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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug tree-optimization/99726] [10/11 Regression] ICE in
 create_intersect_range_checks_index, at tree-data-ref.c:1855 since
 r10-4762-gf9d6338bd15ce1fae36bf25d3a0545e9678ddc58
Date: Mon, 29 Mar 2021 16:31:10 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D99726

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
And -flive-patching=3Dinline-clone -mavx512f -O2 -floop-nest-optimize
-ftree-loop-vectorize -ftrapv -m32
is sufficient to trigger it.
I'm afraid I'm lost in what exactly the code wants to do.
dr_a.dr:
#(Data Ref:=20
#  bb: 57=20
#  stmt: _231 =3D a[_238][_242];
#  ref: a[_238][_242];
#  base_object: a;
#  Access function 0: {(unsigned int) (_239 - graphite_IV.18_206) + 2, +,
4294967295}_6
#  Access function 1: {((unsigned int) (graphite_IV.18_206 + _234) + e.6_19=
) +
4294967295, +, 1}_6
#)
dr_b.dr:
#(Data Ref:=20
#  bb: 57=20
#  stmt: a[_250][_254] =3D _243;
#  ref: a[_250][_254];
#  base_object: a;
#  Access function 0: {(unsigned int) (_251 - graphite_IV.18_206) + 1, +,
4294967295}_6
#  Access function 1: {(unsigned int) (graphite_IV.18_206 + _247) + e.6_19,=
 +,
1}_6
#)

DR_STEP (dr_a.dr) =3D=3D DR_STEP (dr_b.dr) =3D=3D 4092, so it is not neg_st=
ep:
  bool neg_step =3D tree_int_cst_compare (DR_STEP (dr_a.dr), size_zero_node=
) < 0;

      /* Index must evaluate in the same direction as DR.  */
      gcc_assert (!neg_step || tree_int_cst_sign_bit (idx_step) =3D=3D 1);
but this doesn't check anything if neg_step is false, rather than ensuring =
it
has the same direction.
And
      offset_int abs_idx_step =3D offset_int::from (wi::to_wide (idx_step),
                                                  SIGNED);
      if (neg_step)
        abs_idx_step =3D -abs_idx_step;
offset_int::from will treat the unsigned int idx_step of -1U as -1 and the
asserts fail because it is not non-negative.=