Which ONE of the following techniques used in compiler code optimization uses live variable analysis?

Live variable analysis determines whether the value held in a variable at a given point in a program may be read later along some execution path before being redefined.

• Register assignment to variables (Option B): Compilers use liveness analysis to construct an interference graph of live ranges. Two variables whose live ranges do not overlap (i.e., they are not simultaneously live) can be assigned to the same processor register, making live variable analysis central to register allocation and assignment.

• Run-time function call management (Option A): Involves stack frames/activation records managed during program execution, not compiler optimization via data-flow analysis.

• Strength reduction (Option C): Replaces computationally expensive operations (e.g., $x \times 2$) with cheaper equivalent operations (e.g., $x + x$ or $x \ll 1$), using induction variable analysis rather than liveness analysis.

• Constant folding (Option D): Evaluates operations on known constants at compile time (e.g., simplifying $3 + 4$ to $7$) and does not depend on live variable analysis.

Hence, the correct option is (B).