[Bug tree-optimization/54735] [4.8 Regression] Segmentation fault in walk_aliased_vdefs_1

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54735

--- Comment #12 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-10-02 13:03:07 UTC ---
Actually that just papers over the real issue.  The issue is that
cfg-cleanup runs before update-ssa and that removes a basic-block (9)
because we have

<bb 8>:
D.2778 ={v} {CLOBBER};
if (1 == 0)
  goto <bb 9>;
else
  goto <bb 33>;

  <bb 9>:
  # .MEM_62 = VDEF <.MEM_60>
  D.2632.m_col = 0;

  <bb 10>:
  # VUSE <.MEM_62>
  __assert_fail (0);

but as you can see this removes the definition for .MEM_62!

That is what confuses update-SSA (rightfully so - it re-assigns .MEM_62
to the inserted PHI node).

Which means we need to update virtual SSA form right here, before
calling cfgcleanup.