Global optimization techniques in Compiler Design - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the main goal of global optimization techniques in compiler design?

The main goal is to improve the performance and efficiency of the entire program by optimizing code across different parts, not just within a single block or function.

beginner

Explain the difference between local and global optimization.

Local optimization focuses on improving small sections of code, like a single block, while global optimization looks at the whole program or large parts of it to find better improvements.

intermediate

What is 'constant propagation' in global optimization?

Constant propagation is a technique where the compiler replaces variables that have constant values with those values throughout the program to simplify and speed up the code.

beginner

How does 'dead code elimination' improve program efficiency?

Dead code elimination removes parts of the code that never affect the program's output, reducing size and improving speed.

intermediate

What role does 'loop invariant code motion' play in global optimization?

It moves calculations that do not change inside a loop to outside the loop, so they are done only once, saving time during repeated loop executions.

Which of the following is a global optimization technique?

A Peephole optimization

B Register allocation

C Instruction scheduling

D Constant propagation

Constant propagation is a global optimization because it replaces constants throughout the program, while others are more local or machine-level.

What does dead code elimination remove?

A Code that never runs or affects output

B Loops that run too many times

C Variables with constant values

D Function calls

Dead code elimination removes code that does not affect the program's behavior or output.

Loop invariant code motion helps by:

A Moving code inside loops

B Moving code outside loops if it doesn't change

C Removing loops

D Duplicating loop code

It moves calculations that do not change inside loops to outside, reducing repeated work.

Global optimization techniques are applied:

A Only within a single basic block

B Only during machine code generation

C Across multiple blocks or functions

D Only at runtime

Global optimizations analyze and improve code across multiple blocks or functions.

Which optimization replaces variables with their known constant values?

A Constant propagation

B Inlining

C Loop unrolling

D Dead code elimination

Constant propagation replaces variables with constant values to simplify code.

Describe three common global optimization techniques and how they improve program performance.

Think about how each technique reduces unnecessary work or simplifies code.

Explain why global optimization is more powerful than local optimization in compiler design.

Consider how looking at the entire program helps find more opportunities.