[Bug tree-optimization/32353] New: [4.1/4.2 Regression] Miscompilation with RESULT_DECL

[jakub at gcc dot gnu dot org]

extern "C" void abort ();

struct A
{
  int f;
  A (int x) : f (x) {}
};

A
foo (const A &x, const A &y)
{
  A r (0);
  r = x.f == -111 ? y : (y.f == -111 || x.f > y.f) ? x : y;
  A s (0);
  r = r.f == -111 ? s : (r.f > s.f) ? r : s;
  return r;
}

int
main ()
{
  A a (A(0));
  int b[] = { 1, 2, 9 };
  for (int i = 0; i < 3; i++)
    {
      A c (b[i]);
      if (foo (a, c).f != b[i])
        abort ();
      a = c;
    }
}

is miscompiled on i?86-linux with -O2 -m32.  From quick glance at the dumps,
dce3 removes a needed statement:
<retval>.fD.2005 = SR.23D.2103_26;
but already *.alias1 seems to be wrong:
  # BLOCK 11
  # PRED: 10 (true)
<L8>:;
  iftmp.3D.2049_27 = &<retval>;
  goto <bb 13> (<L10>);
  # SUCC: 13 (fallthru)

  # BLOCK 12
  # PRED: 10 (false)
<L9>:;
  iftmp.3D.2049_28 = &sD.2036;
  # SUCC: 13 (fallthru)

  # BLOCK 13
  # PRED: 11 (fallthru) 12 (fallthru)
  # iftmp.3D.2049_2 = PHI <iftmp.3D.2049_27(11), iftmp.3D.2049_28(12)>;
<L10>:;
  iftmp.2D.2047_29 = iftmp.3D.2049_2;
  goto <bb 15> (<L12>);
  # SUCC: 15 (fallthru)

  # BLOCK 14
  # PRED: 9 (false)
<L11>:;
  iftmp.2D.2047_30 = &sD.2036;
  # SUCC: 15 (fallthru)

  # BLOCK 15
  # PRED: 13 (fallthru) 14 (fallthru)
  # iftmp.2D.2047_1 = PHI <iftmp.2D.2047_29(13), iftmp.2D.2047_30(14)>;
<L12>:;
  #   D.2051_32 = V_MUST_DEF <D.2051_31>;
  #   VUSE <SFT.6D.2086_23>;
  D.2051 = *iftmp.2D.2047_1;

Note that iftmp.2D.2047_1 can be either &sD.2036 (in that case it really VUSEs
SFT.6D.2086_23), but it can also be &<retval> and that's not stored anywhere.


-- 
           Summary: [4.1/4.2 Regression] Miscompilation with RESULT_DECL
           Product: gcc
           Version: 4.1.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: jakub at gcc dot gnu dot org
GCC target triplet: i386-linux


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=32353