The pass pipeline of some architecture splits register allocation
phase based on different register classes. As some analyses need to
be computed at the beginning of the register allocation and kept
alive till all values are assigned to some physical registers.

This poses challenge with objective of introducing StackSlotColoring
after partial virtual registers are assigned to physical registers,
in order to optimize stack slots usage.As this pass doesn't preserve
few analysis yet to be needed by the register allocation of the
remaining virtual registers, necessiating them to be kept preserved.