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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug middle-end/39275] -funroll-loop fails
Date: Sat, 21 Jan 2012 08:11:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39275

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> 2012-01-21 07:20:42 UTC ---
Here is a reduced testcase:
struct vector
{
  char *_M_start;
  char *_M_finish;
};
struct LoopBase
{
  static LoopBase *f();
  LoopBase *ParentLoop;
  vector SubLoops;
  ~LoopBase() 
  {
    for (int i = 0, e = SubLoops._M_finish - SubLoops._M_start; i != e; ++i)  
      delete f();
  }
};
void deleteLoopFromQueue(LoopBase *L, int b)
{
  if (L->ParentLoop)
    while (L->SubLoops._M_start != L->SubLoops._M_finish)return;
  else 
   while (L->SubLoops._M_start != L->SubLoops._M_finish)return;
  delete L;
}

--- CUT ---
The delete loop is actually an empty loop but the tree level does not see that
for some reason:
  # prephitmp.36_112 = PHI <prephitmp.36_6(4), prephitmp.36_3(3)>
  # prephitmp.36_21 = PHI <prephitmp.36_6(4), prephitmp.36_3(3)>
  D.2385_15 = (long int) prephitmp.36_21;
  D.2387_17 = (long int) prephitmp.36_112;

Those PHIs are the same.