[Bug bootstrap/36908] [4.4 Regression] bootstrap forever with BOOT_CFLAGS="-O2 -ftree-loop-distribution"

["jakub at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #3 from jakub at gcc dot gnu dot org  2008-09-02 16:44 -------
Why got this even marked as regression?  GCC 4.3.1 didn't support
-ftree-loop-distribution, it is a new option, so it can't regress.
The loop in question is:
<bb 8>:
  # state_89 = PHI <state_17(9), state_5(7)>
  # prephitmp.18_6 = PHI <state_89(9), pretmp.17_59(7)>
  state_17 = state_89->next_alt_state;
  state_89->next_alt_state = prephitmp.18_6;
  first_free_alt_state_lsm.29_18 = state_89;
  if (state_17 != 0B)
    goto <bb 9>;
  else
    goto <bb 10>;

<bb 9>:
  goto <bb 8>;
and gets distributed into:
<bb 16>:
  # state_62 = PHI <state_22(17), state_5(7)>
  # prephitmp.18_26 = PHI <state_62(17), pretmp.17_59(7)>
  state_22 = state_62->next_alt_state;
  state_62->next_alt_state = prephitmp.18_26;
  if (state_22 != 0B)
    goto <bb 17>;
  else
    goto <bb 18>;

<bb 17>:
  goto <bb 16>;

<bb 18>:
  # prephitmp.18_90 = PHI <prephitmp.18_26(16)>

<bb 8>:
  # state_89 = PHI <state_17(9), state_5(18)>
  state_17 = state_89->next_alt_state;
  state_89->next_alt_state = prephitmp.18_90;
  first_free_alt_state_lsm.29_18 = state_89;
  if (state_17 != 0B)
    goto <bb 9>;
  else
    goto <bb 10>;

<bb 9>:
  goto <bb 8>;
Perhaps tree-loop-distribution.c is confused by a PHI depending on previous PHI
result?


-- 

jakub at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |spop at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36908