This is the unsigned variant of D111976, where we convert a clamped fptoui to a fptoui.sat. Because we are unsigned, the condition this time is only UMIN of UINT_MAX. Similarly to D111976 it handles ISD::UMIN, ISD::SETCC/ISD::SELECT, ISD::VSELECT or ISD::SELECT_CC nodes.
This especially helps on ARM/AArch64 where the vcvt instructions naturally saturate the result.
Isn't this (C1 + 1).exactLogBase2()?