 Register allocation

Register allocation maps temporary values or virtual registers in a compiler's representation to a limited supply of physical processor registers. A value's live range covers where it may still be needed. Overlapping live ranges constrain which values can share a processor register; register spilling moves some storage into computer memory when necessary.^[ref]

For example, in a=x+y; b=a*z, the processor register holding a can hold b after a's final use, if the target operation permits. If both values are needed later, overwriting a would lose required information. An interference graph represents simultaneous storage requirements, connecting register allocation to graph coloring. Real targets add constraints from register classes, reserved registers, calling conventions and particular machine instructions; minimizing the number of names alone does not solve the whole problem.