[Bug target/102124] [11/12 Regression] -ftree-loop-vectorize Causing Data To Lose Sign Bit on AARCH64 Platform

[jakub at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102124

--- Comment #3 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Before vectorization the loop body is:
  _1 = a_19(D) + i_29;
  _2 = *_1;
  _3 = (int) _2;
  _4 = b_20(D) + i_29;
  _5 = *_4;
  _6 = (int) _5;
  _7 = _3 - _6;
  ab_21 = _7 | ab_25;
  _10 = _6 - _3;
  ba_22 = _10 | ba_27;
where _2 and _5 are unsigned char and _3, _6, _7, _10 are int.
It is vectorized as
  vect_patt_54.17_61 = WIDEN_MINUS_LO_EXPR <vect__2.13_56, vect__5.16_17>;
  vect_patt_54.17_62 = WIDEN_MINUS_HI_EXPR <vect__2.13_56, vect__5.16_17>;
  vect_patt_53.18_63 = [vec_unpack_lo_expr] vect_patt_54.17_61;
  vect_patt_53.18_64 = [vec_unpack_hi_expr] vect_patt_54.17_61;
  vect_patt_53.18_65 = [vec_unpack_lo_expr] vect_patt_54.17_62;
  vect_patt_53.18_66 = [vec_unpack_hi_expr] vect_patt_54.17_62;
  _7 = _3 - _6;
  vect_ab_21.19_67 = vect_patt_53.18_63 | vect_ab_25.9_13;
  vect_ab_21.19_68 = vect_patt_53.18_64 | vect_ab_21.19_67;
  vect_ab_21.19_69 = vect_patt_53.18_65 | vect_ab_21.19_68;
  vect_ab_21.19_70 = vect_patt_53.18_66 | vect_ab_21.19_69;
  ab_21 = _7 | ab_25;
which means it is vectorized as if it was instead of (int) _2 - (int) _6
(int) (unsigned short) ((unsigned short) _2 - (unsigned short) _6).