[Bug tree-optimization/59058] wrong code at -O3 on x86_64-linux-gnu (affecting gcc 4.6 to trunk)

[glisse at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59058

--- Comment #1 from Marc Glisse <glisse at gcc dot gnu.org> ---
For the vectorizer issue on trunk, this is enough:

int printf (const char *, ...);

short b = 0; 

int 
main ()
{
  int c = 0;
l1:
  b++;
  c |= b;
  if (b)
    goto l1;
  printf ("%d\n", c);
  return 0;
}

This code relies on the gcc extension that casting to a shorter integer is done
modulo 2. Note that if we move the declaration of b inside the function, the
compiler (wrongly?) warns:
s.c:11:4: warning: iteration 32767u invokes undefined behavior
[-Waggressive-loop-optimizations]
   b++;
    ^
s.c:13:6: note: containing loop
   if (b)
      ^
(and the return value changes from 7 to 131071)


2 missed optimizations while looking at the dumps:

  stmp_var_.12_46 = _4 + 1;
  stmp_var_.12_47 = _4 + 2;
  stmp_var_.12_48 = _4 + 3;
  stmp_var_.12_49 = _4 + 4;
  stmp_var_.12_50 = _4 + 5;
  stmp_var_.12_51 = _4 + 6;
  stmp_var_.12_52 = _4 + 7;
  vect_cst_.13_53 = {_4, stmp_var_.12_46, stmp_var_.12_47, stmp_var_.12_48,
stmp_var_.12_49, stmp_var_.12_50, stmp_var_.12_51, stmp_var_.12_52};

This should really be:

  v = { _4, _4, ... };
  w = v + { 0, 1, 2, ... };

Also:

  vector(8) unsigned short vect_b.17;
  vector(8) short int vect_vec_iv_.16;
  vector(8) unsigned short vect_vec_iv_.15;
[...]
  vect_vec_iv_.16_57 = VIEW_CONVERT_EXPR<vector(8) short
int>(vect_vec_iv_.15_55);
  vect_vec_iv_.15_56 = vect_vec_iv_.15_55 + vect_cst_.14_54;
  vect_b.17_58 = VIEW_CONVERT_EXPR<vector(8) unsigned
short>(vect_vec_iv_.16_57);

vect_b.17_58 is vect_vec_iv_.15_55, not sure why we don't see through that.