[Bug tree-optimization/94566] conversion between std::strong_ordering and int

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94566

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
So for conv2 the most immediate issue is that we're failing to sink and common
the assignment to D.8516._M_value (I had patches for this).

conv2 (int i)
{
  int i_2(D) = i;
  struct strong_ordering D.8516;

  <bb 2> [local count: 1073741824]:
  if (i_2(D) == 0)
    goto <bb 5>; [33.33%]
  else
    goto <bb 3>; [66.67%]

  <bb 3> [local count: 1073741824]:
  if (i_2(D) == 1)
    goto <bb 6>; [50.00%]
  else
    goto <bb 4>; [50.00%]

  <bb 4> [local count: 357878150]:
  D.8516._M_value = -1;
  goto <bb 7>; [100.00%]

  <bb 5> [local count: 357878150]:
  D.8516._M_value = 0;
  goto <bb 7>; [100.00%]

  <bb 6> [local count: 357878150]:
  D.8516._M_value = 1;

  <bb 7> [local count: 1073634451]:
  return D.8516;

for conv1 this is a missed phi-opt, at phiopt2 time:

conv1 (struct strong_ordering s)
{
  int SR.4;
  int _1;

  <bb 2> [local count: 1073741824]:
  SR.4_4 = s._M_value;
  if (SR.4_4 == -1)
    goto <bb 6>; [50.00%]
  else
    goto <bb 3>; [50.00%]

  <bb 3> [local count: 536870913]:
  if (SR.4_4 == 0)
    goto <bb 6>; [50.00%]
  else
    goto <bb 4>; [50.00%]

  <bb 4> [local count: 268435456]:
  if (SR.4_4 == 1)
    goto <bb 6>; [100.00%]
  else
    goto <bb 5>; [0.00%]

  <bb 5> [count: 0]:
  __builtin_unreachable ();

  <bb 6> [local count: 1073741824]:
  # RANGE [-1, 1]
  # _1 = PHI <-1(2), 0(3), 1(4)>
  return _1;

it's a bit of a convoluted case of course but the only chance to pattern
match this ...