Local optimization (peephole) in Compiler Design - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is local optimization (peephole) in compiler design?

Local optimization, also called peephole optimization, is a technique where the compiler looks at a small set of instructions (a "peephole") and tries to replace them with a more efficient sequence without changing the program's behavior.

beginner

Why is peephole optimization called 'local' optimization?

Because it focuses on a small, localized part of the code—usually just a few instructions at a time—rather than analyzing the entire program or large blocks of code.

beginner

Give an example of a simple peephole optimization.

Replacing a sequence like "LOAD A; LOAD A" with just "LOAD A" because loading the same value twice is redundant.

intermediate

What kinds of improvements can peephole optimization achieve?

It can reduce the number of instructions, remove redundant operations, simplify calculations, and improve execution speed and code size.

intermediate

What is a limitation of peephole optimization?

It only looks at small instruction windows and cannot optimize across larger code blocks or consider global program behavior.

What does peephole optimization primarily focus on?

A Small sequences of instructions

B Entire program structure

C Memory allocation

D User interface design

Peephole optimization looks at small windows of instructions to improve them locally.

Which of the following is an example of peephole optimization?

A Changing variable names for clarity

B Replacing 'LOAD A; LOAD A' with 'LOAD A'

C Rearranging functions in a file

D Adding comments to code

Removing redundant loads is a classic peephole optimization.

What is a key benefit of peephole optimization?

A Improves code readability

B Increases program size

C Reduces instruction count

D Changes program logic

Peephole optimization reduces instructions to make code faster and smaller.

Which is NOT a characteristic of peephole optimization?

A Simplifies calculations

B Works on small instruction windows

C Removes redundant instructions

D Analyzes entire program flow

Peephole optimization does not analyze the entire program, only small parts.

Why might peephole optimization miss some improvements?

A It only looks at small parts of code

B It changes program logic

C It requires user input

D It only works on source code comments

Because peephole optimization focuses on small instruction sets, it can miss larger optimization opportunities.

Explain what local optimization (peephole) is and why it is useful in compiler design.

Think about how looking at just a few instructions can help make code faster or smaller.

Describe a simple example of peephole optimization and its effect on the code.

Consider removing repeated instructions or simplifying calculations.