[Bug tree-optimization/26939] PRE confuses loop number of iterations analysis

[rguenth at gcc dot gnu dot org]

------- Comment #1 from rguenth at gcc dot gnu dot org  2006-03-30 12:22 -------
Note this testcase requires the fix(es) for PR26900 to figure out the number of
iterations for the inner loop.  The failure to figure out the number of
iterations of the outer loop can be reproduced with mainline.  Basically we
have (in the working case with using j-1):


foo (i1, j1)
{
  int pretmp.20;
  int j;
  int i;
  int D.1534;

<bb 2>:
  if (j1_4 >= 0) goto <L14>; else goto <L5>;

<L14>:;
  goto <bb 8> (<L2>);

<L16>:;

  # i_14 = PHI <i_9(4), 0(9)>;
<L1>:;
  D.1534_8 = pretmp.20_10;
  bar (pretmp.20_10);
  i_9 = i_14 + 1;
  if (i1_6 >= i_9) goto <L16>; else goto <L3>;

<L3>:;
  j_7 = j_12 + 1;
  if (j1_4 >= j_7) goto <L18>; else goto <L5>;

<L18>:;

  # j_12 = PHI <j_7(7), 0(3)>;
<L2>:;
  if (i1_6 >= 0) goto <L20>; else goto <L3>;

<L20>:;
  pretmp.20_10 = j_12 - 1;
  goto <bb 5> (<L1>);

<L5>:;
  return;

}

while with using j+1 we get

foo (i1, j1)
{
  int prephitmp.21;
  int pretmp.20;
  int j;
  int i;
  int D.1534;

<bb 2>:
  if (j1_4 >= 0) goto <L14>; else goto <L5>;

<L14>:;
  goto <bb 9> (<L2>);

<L16>:;

  # i_14 = PHI <i_9(4), 0(11)>;
<L1>:;
  D.1534_8 = pretmp.20_13;
  bar (pretmp.20_13);
  i_9 = i_14 + 1;
  if (i1_6 >= i_9) goto <L16>; else goto <L17>;

  # D.1534_2 = PHI <pretmp.20_13(5)>;
<L17>:;

  # prephitmp.21_11 = PHI <D.1534_2(6), pretmp.20_1(10)>;
<L3>:;
  j_7 = prephitmp.21_11;
  if (j1_4 >= prephitmp.21_11) goto <L18>; else goto <L5>;

<L18>:;

  # j_12 = PHI <prephitmp.21_11(8), 0(3)>;
<L2>:;
  if (i1_6 >= 0) goto <L20>; else goto <L21>;

<L21>:;
  pretmp.20_1 = j_12 + 1;
  goto <bb 7> (<L3>);

<L20>:;
  pretmp.20_13 = j_12 + 1;
  goto <bb 5> (<L1>);

<L5>:;
  return;

}


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=26939