[Bug tree-optimization/67962] Optimization opportunity with conditional swap to two MIN/MAX in phiopt

[rguenth at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67962

--- Comment #4 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Andrew Pinski from comment #3)
> Mine, but for gcc 13.  The main problem I see if two cmov might be slower
> than a branch on x86_64 processors.

Two cmov definitely, a min/max pair not.

Now, phiopt will turn

  <bb 2> :
  if (y_16(D) < x_17(D))
    goto <bb 3>; [INV]
  else
    goto <bb 4>; [INV]

  <bb 3> :

  <bb 4> :
  # x_14 = PHI <x_17(D)(2), y_16(D)(3)>
  if (y_16(D) < x_17(D))
    goto <bb 5>; [INV]
  else
    goto <bb 6>; [INV]

  <bb 5> :

  <bb 6> :
  # y_15 = PHI <y_16(D)(2), x_17(D)(3)>

into the desired pair but fails for the equivalent

  <bb 2> :
  if (y_16(D) < x_17(D))
    goto <bb 3>; [INV]
  else
    goto <bb 4>; [INV]

  <bb 3> :

  <bb 4> :
  # x_14 = PHI <x_17(D)(2), y_16(D)(3)>
  # y_15 = PHI <y_16(D)(2), x_17(D)(3)>

We do value-replacement for more than one PHI but not others, not exactly
sure why.  We could dry-run convert all PHIs and only if that succeeds
and the condition goes away perform the transforms.  Of course some
transforms might still not be profitable then.