[Bug tree-optimization/56918] [4.8 Regression] incorrect auto-vectorization of array initialization

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56918



--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> 2013-04-11 
11:59:05 UTC ---

The vectorizer does nothing wrong.  The bug goes away with -fdisable-tree-vrp2

which would expose



-  stmp_var_.3_2 = 0 + 1;

-  stmp_var_.3_19 = stmp_var_.3_2 + 1;

-  stmp_var_.3_20 = stmp_var_.3_19 + 1;

-  vect_cst_.4_21 = {0, stmp_var_.3_2, stmp_var_.3_19, stmp_var_.3_20};

+  stmp_var_.3_2 = 1;

+  stmp_var_.3_19 = 2;

+  stmp_var_.3_20 = 3;

+  vect_cst_.4_21 = { 0, 1, 2, 3 };



(ick, unfolded 0 + 1)



so we expand



  vect_patt.11_29 = { 2, 3, 4, 5 } >> 31;

  vect_patt.12_30 = { -1, -1, -1, -1 } - vect_patt.11_29;

  vect_patt.13_32 = vect_patt.12_30 * { 3, 3, 3, 3 };

  vect_patt.15_33 = { 2, 3, 4, 5 } - vect_patt.13_32;

  vect_var_.16_35 = vect_patt.15_33 + { 1, 1, 1, 1 };

  vect_var_.18_36 = [vec_unpack_float_lo_expr] vect_var_.16_35;

  vect_var_.18_37 = [vec_unpack_float_hi_expr] vect_var_.16_35;

  MEM[(double[1024] *)&data] = vect_var_.18_36;

  MEM[(double[1024] *)&data + 16B] = vect_var_.18_37;

  _10 = data[0];

  if (_10 != 3.0e+0)



where I bet that unfolded constant expressions are somehow mis-handled.