[Bug tree-optimization/126139] phiopt does not if-convert half diamonds with multiple PHIs

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126139

--- Comment #6 from Drea Pinski <pinskia at gcc dot gnu.org> ---
So my new plan (after sleeping on it) for this is finding this pattern in the
loop. and see if we can change this into a min/max and remove the condition in
the first place.

This will fix the vectorization too.