Consider the following intermediate program in three address code p = a - b q…

CONCEPT: Static single assignment (SSA) gives every definition a distinct versioned name. Each use must refer to the version produced by the definition that reaches that program point; the particular subscripts are arbitrary, but definition-use links are not.

APPLICATION: Trace the four statements in source order and create a fresh name at each assignment.

1. The first definition of p becomes p3 = a - b.

2. The next statement uses that reaching definition, so it becomes q4 = p3 * c.

3. The later assignment to p creates a new version: p4 = u * v.

4. The final statement uses the newest p and the earlier q, so it becomes q5 = p4 + q4.

CROSS-CHECK: The left-hand names p3, q4, p4, and q5 each occur as a definition exactly once. Every right-hand version has already been defined, and the final expression preserves the original dependence on the second p value and the first q value.

Therefore the SSA form is p3 = a - b; q4 = p3 * c; p4 = u * v; q5 = p4 + q4.