Question

The identification of common sub-expression and replacement of run-time computations by compile-time computation is:

• A. Local optimization
• B. Loop optimization
• C. Constant folding
• D. Data flow analysis

Hint:

Constant folding improves performance by evaluating constant expressions at compile time, reducing unnecessary runtime computations.

Answer 1

The Correct Option is C

Step 1: Understanding Constant Folding Constant folding is an optimization technique where constant expressions are evaluated at compile time rather than at runtime. For example: \[ \text{int x = 3 + 5;} \] This is replaced with: \[ \text{int x = 8;} \]
Step 2: Why Constant Folding?
- Reduces runtime computation.
- Optimizes performance by eliminating unnecessary calculations.
- Common in compiler optimization passes.

Step 3: Evaluating options:
- (A) Incorrect: Local optimization improves performance within basic blocks but does not specifically perform constant folding.
- (B) Incorrect: Loop optimization enhances loop execution but does not replace compile-time computations.
- (C) Correct: Constant folding replaces runtime expressions with precomputed values.
- (D) Incorrect: Data flow analysis is used for optimization but does not replace runtime computation with constants.