[Bug middle-end/60418] [4.9 Regression] 435.gromacs in SPEC CPU 2006 is miscompiled

[hjl.tools at gmail dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60418

--- Comment #20 from H.J. Lu <hjl.tools at gmail dot com> ---
(In reply to Richard Biener from comment #13)
> Huh, adding a pre-header should _never_ do sth like that.  Can you produce
> a small testcase that exhibits these kind of changes with adding/removing
> a preheader?

copyprop2 pass removed a preheader and cunrolli pass added it back:

  <bb 3>:
  # n_213 = PHI <1(2)> 

  <bb 8>:
  # n_8 = PHI <n_213(3), n_218(9)>

copyprop3 pass optimized it to

  <bb 3>:
  n_213 = 1;

  <bb 4>:
  # n_8 = PHI <1(3), n_218(7)>

Then the unused n_213 disappeared in reassoc1 pass and n_213 was
put on FREE_SSANAMES.