For a statement $S$ in a program, in the context of liveness analysis, the following sets are defined: $USE(S)$ : the set of variables used in $S$ $IN(S)$ : the set of variables that are live at the entry of $S$ $OUT(S)$ : the set of variables that are live at the exit of $S$ Consider a basic block that consists of two statements, $S_1$ followed by $S_2$. Which one of the following statements is correct?

In a basic block, execution is strictly sequential, meaning the statement immediately following $S_1$ is $S_2$.

In liveness analysis (a backward data-flow analysis):

• The information at the exit of a statement $S_1$, denoted as $OUT(S_1)$, represents the set of variables that need to be live immediately after $S_1$ finishes execution.

• Since control flows directly from $S_1$ into $S_2$ without any branching or intervening operations, the variables live at the exit of $S_1$ are precisely the variables live at the entry of $S_2$.

Therefore:

Hence, (A) is the correct option.