[Bug tree-optimization/46693] incorrect code generation with -O2 optimization enabled

[ramana at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46693

Ramana Radhakrishnan <ramana at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |ASSIGNED
          Component|target                      |tree-optimization

--- Comment #9 from Ramana Radhakrishnan <ramana at gcc dot gnu.org> 2010-12-13 10:53:31 UTC ---
On trunk 

vrp converts the IR from :


<bb 3>:
  c_5 = D.2034_4;
  D.2026_6 = D.2034_4 == 13;
  D.2027_7 = D.2034_4 == 10;
  D.2028_8 = D.2026_6 || D.2027_7;
  if (D.2028_8 != 0)
    goto <bb 7>;
  else
    goto <bb 4>;

<bb 4>:
  D.2030_9 = D.2034_4 <= 31;
  D.2031_10 = D.2034_4 != 9;
  D.2032_11 = D.2030_9 && D.2031_10;
  if (D.2032_11 != 0)
    goto <bb 7>;
  else
    goto <bb 5>;

<bb 5>:
  str_12 = str_1 + 1;

<bb 6>:
  # str_1 = PHI <str_3(D)(2), str_12(5)>
  D.2034_4 = *str_1;
  if (D.2034_4 != 0)
    goto <bb 3>;
  else
    goto <bb 7>;

<bb 7>:
  # D.2033_2 = PHI <0(4), 1(6), 0(3)>
  return D.2033_2;


to

<bb 3>:
  c_5 = D.2034_4;
  D.2026_6 = D.2034_4 == 13;
  D.2027_7 = D.2034_4 == 10;
  D.2028_8 = D.2026_6 | D.2027_7;
  if (D.2028_8 != 0)
    goto <bb 7>;
  else
    goto <bb 4>;

<bb 4>:
  D.2030_9 = D.2034_4 <= 31;
  D.2031_10 = D.2034_4 != 9;
  D.2032_11 = D.2030_9 & D.2031_10;
  if (D.2032_11 != 0)
    goto <bb 7>;
  else
    goto <bb 5>;

<bb 5>:
  str_12 = str_1 + 1;

<bb 6>:
  # str_1 = PHI <str_3(D)(2), str_12(5)>
  D.2034_4 = *str_1;
  if (D.2034_4 != 0)
    goto <bb 3>;
  else
    goto <bb 7>;

<bb 7>:
  # D.2033_2 = PHI <0(4), 1(6), 0(3)>
  return D.2033_2;

After a while ifcombine comes along and removes basic block 5 and merges blocks
3 and 4 into 1 basic block because it thinks that the 


optimizing two comparisons to 1
Merging blocks 3 and 4
Removing basic block 5

and converts this to this form: 

<bb 2>:
  goto <bb 4>;


<bb 3>:
  D.2026_6 = D.2034_4 == 13;
  D.2027_7 = D.2034_4 == 10;
  D.2028_8 = D.2026_6 | D.2027_7;
  D.2030_9 = D.2034_4 <= 31;
  D.2031_10 = D.2034_4 != 9;
  D.2032_11 = D.2030_9 & D.2031_10;
  goto <bb 5>;

<bb 4>:
Invalid sum of incoming frequencies 873, should be 10000
  # str_1 = PHI <str_3(D)(2)>
  D.2034_4 = *str_1;
  if (D.2034_4 != 0)
    goto <bb 3>;
  else
    goto <bb 5>;

<bb 5>:
Invalid sum of incoming frequencies 10000, should be 873
  # D.2033_2 = PHI <0(3), 1(4)>
  return D.2033_2;