Local optimization (peephole) in Compiler Design - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

What is the primary goal of peephole optimization in compilers?

Peephole optimization is a technique used in compilers. What is its main purpose?

A To optimize small sequences of instructions locally for better performance or size

B To improve the overall program logic by changing algorithms

C To translate high-level code directly into machine code

D To perform syntax checking and error reporting

💡 Hint

Think about small code segments and local improvements.

Peephole optimization focuses on small windows of instructions to replace inefficient patterns with better ones, improving speed or reducing code size without changing program behavior.

📋 Factual

intermediate

Which of the following is a common peephole optimization technique?

Identify the typical peephole optimization from the options below.

A Loop unrolling to reduce loop overhead

B Inlining functions to avoid call overhead

C Replacing a sequence of instructions with a single equivalent instruction

D Register allocation across the entire program

💡 Hint

Focus on small instruction sequences and their replacement.

Peephole optimization often replaces multiple instructions with a single, more efficient instruction to improve performance or reduce code size.

🔍 Analysis

advanced

What is the output of the peephole optimizer on this instruction sequence?

Given the following assembly instructions, what will a peephole optimizer most likely produce?

Compiler Design

MOV R1, R2
MOV R2, R1
ADD R1, #0

A

MOV R1, R2
MOV R2, R1
ADD R1, #0

B MOV R1, R2

C

NOP
NOP
NOP

D

MOV R1, R2
NOP

💡 Hint

Consider redundant moves and adding zero.

The second MOV reverses the first, so both cancel out. Adding zero does nothing. The optimizer removes redundant instructions, leaving only the effective MOV.

❓ Reasoning

advanced

Why might peephole optimization sometimes be limited in improving program performance?

Choose the best explanation for the limitations of peephole optimization.

A It increases the size of the compiled code

B It only works on high-level source code, not machine code

C It requires manual intervention by the programmer

D It focuses on small instruction windows and cannot optimize across larger code structures

💡 Hint

Think about the scope of peephole optimization.

Peephole optimization looks at small groups of instructions and cannot analyze or optimize larger program structures or algorithms, limiting its impact.

❓ Comparison

expert

Compare peephole optimization with global optimization in compilers.

Which statement correctly contrasts peephole optimization with global optimization?

A Peephole optimization analyzes entire programs, while global optimization only looks at small instruction sequences

B Global optimization can optimize across functions and modules, whereas peephole optimization only works on local instruction windows

C Peephole optimization requires source code changes, global optimization does not

D Global optimization is faster and simpler than peephole optimization

💡 Hint

Consider the scope and scale of each optimization type.

Peephole optimization works on small, local instruction sequences, while global optimization analyzes larger program parts, including multiple functions or modules, to improve performance more broadly.