Strength reduction in Compiler Design - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is strength reduction in compiler design?

Strength reduction is a compiler optimization technique that replaces expensive operations with equivalent but cheaper ones to improve performance.

beginner

Give an example of strength reduction.

Replacing multiplication inside a loop with addition. For example, changing i * 4 to repeated addition like i + i + i + i or better, using a running sum.

beginner

Why is strength reduction useful in loops?

Because loops run many times, replacing costly operations like multiplication or division with cheaper ones like addition or subtraction saves time and speeds up the program.

intermediate

Which of these operations is typically replaced during strength reduction?

Multiplication or division operations are often replaced by addition or subtraction to reduce computational cost.

intermediate

Can strength reduction affect the correctness of a program?

No, strength reduction changes how calculations are done but keeps the results the same, so the program's behavior remains correct.

What does strength reduction replace in code?

A Functions with loops

B Variables with constants

C Expensive operations with cheaper ones

D Loops with recursion

Strength reduction replaces costly operations like multiplication with cheaper ones like addition.

Which operation is commonly replaced by addition in strength reduction?

A Addition

B Multiplication

C Subtraction

D Modulo

Multiplication is often replaced by addition to reduce computation cost.

Why is strength reduction especially useful inside loops?

A Loops run many times, so saving cost per iteration adds up

B Loops cannot have multiplication

C Loops are slow by default

D Loops run once

Because loops repeat many times, optimizing operations inside them greatly improves performance.

Which of these is NOT a goal of strength reduction?

A Replace expensive operations

B Improve program speed

C Maintain program correctness

D Reduce power consumption

Strength reduction focuses on speed and correctness, not directly on power consumption.

Strength reduction can be described as:

A Replacing slow operations with faster equivalents

B Adding more loops to the program

C Changing program output

D Removing variables

It replaces slow operations like multiplication with faster ones like addition without changing output.

Explain what strength reduction is and why it is important in compiler optimization.

Think about how changing multiplication to addition inside loops helps speed.

Describe a simple example where strength reduction can be applied in a loop.

Consider calculating an index multiplied by a constant inside a loop.