Global optimization techniques in Compiler Design - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to identify the global optimization technique that removes unreachable code.

Compiler Design

The optimization technique that removes code which can never be executed is called [1].

Drag options to blanks, or click blank then click option'

ADead Code Elimination

BLoop Unrolling

CConstant Folding

DInlining

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing with Loop Unrolling which duplicates loops.

Thinking Constant Folding removes code.

Dead Code Elimination removes code that will never run, improving efficiency.

2fill in blank

medium

Complete the code to name the optimization technique that replaces variables with known constant values.

Compiler Design

Replacing expressions with constant values during compilation is called [1].

Drag options to blanks, or click blank then click option'

ALoop Fusion

BDead Code Elimination

CRegister Allocation

DConstant Folding

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up with Dead Code Elimination.

Confusing with Register Allocation which manages CPU registers.

Constant Folding evaluates constant expressions at compile time to simplify code.

3fill in blank

hard

Fix the error in the statement describing a global optimization technique.

Compiler Design

The technique that duplicates loop bodies to reduce loop overhead is called [1].

Drag options to blanks, or click blank then click option'

ALoop Unrolling

BDead Code Elimination

CInlining

DConstant Propagation

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing with Inlining which replaces function calls.

Thinking Dead Code Elimination duplicates code.

Loop Unrolling duplicates the loop body multiple times to reduce the number of iterations and overhead.

4fill in blank

hard

Fill both blanks to complete the dictionary that maps optimization techniques to their descriptions.

Compiler Design

optimizations = {"Dead Code Elimination": "Removes [1] code", "Loop Unrolling": "Duplicates [2] bodies"}

Drag options to blanks, or click blank then click option'

Aunreachable

Bfunction

Cloop

Dconstant

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'function' instead of 'loop' for Loop Unrolling.

Confusing 'constant' with 'unreachable'.

Dead Code Elimination removes unreachable code, and Loop Unrolling duplicates loop bodies.

5fill in blank

hard

Fill all three blanks to complete the dictionary comprehension that filters optimizations based on a condition.

Compiler Design

filtered = {k: v for k, v in optimizations.items() if k [1] "Loop Unrolling" or v [2] "Removes" and k [3] "Dead Code Elimination"}

Drag options to blanks, or click blank then click option'

A==

Bstartswith

C!=

Dendswith

Attempts:

3 left

💡 Hint

Common Mistakes

Using '==' instead of '!=' to exclude keys.

Confusing 'endswith' with 'startswith'.

The comprehension filters optimizations where the key is not equal to "Loop Unrolling", the value starts with "Removes", and the key equals "Dead Code Elimination".

Practice

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

easy

A. To fix syntax errors in the code

B. To translate code into machine language

C. To improve the performance of the entire program

D. To check for logical errors during runtime

Solution

1. Step 1: Understand the purpose of global optimization

   Global optimization aims to improve the whole program's efficiency, not just parts of it.

2. Step 2: Differentiate from other compiler tasks

   Fixing syntax or translating code are separate compiler phases, not optimization.

3. Final Answer:

   To improve the performance of the entire program -> Option C

4. Quick Check:

   Global optimization = whole program improvement [OK]

Hint: Global optimization means improving the entire program [OK]

Common Mistakes:

• Confusing optimization with syntax checking
• Thinking optimization only fixes errors
• Mixing code translation with optimization

2. Which of the following is a valid example of a global optimization technique?

easy

A. Register allocation

B. Loop-invariant code motion

C. Lexical analysis

D. Syntax parsing

Solution

1. Step 1: Identify global optimization techniques

   Loop-invariant code motion moves calculations out of loops to avoid repeated work.

2. Step 2: Exclude non-optimization tasks

   Syntax parsing and lexical analysis are earlier compiler phases; register allocation is a resource management step.

3. Final Answer:

   Loop-invariant code motion -> Option B

4. Quick Check:

   Moving code out of loops = loop-invariant code motion [OK]

Hint: Look for techniques that reduce repeated work in code [OK]

Common Mistakes:

• Confusing parsing with optimization
• Thinking register allocation is optimization
• Mixing compiler phases

3. Consider this code snippet before optimization:

for (int i = 0; i < n; i++) {
  int x = 5 * 10;
  sum += x;
}

Which global optimization technique can improve this code?

medium

A. Inline expansion

B. Dead code elimination

C. Constant folding

D. Loop-invariant code motion

Solution

1. Step 1: Identify repeated calculation inside the loop

   The expression 5 * 10 does not depend on i and is recalculated every iteration.

2. Step 2: Apply loop-invariant code motion

   Move int x = 5 * 10; outside the loop to avoid repeated calculation.

3. Final Answer:

   Loop-invariant code motion -> Option D

4. Quick Check:

   Move constant calculation out of loop = loop-invariant code motion [OK]

Hint: Move calculations that don't change out of loops [OK]

Common Mistakes:

• Choosing constant folding (done once, but not moving code)
• Confusing dead code elimination with removing unused code
• Thinking inline expansion applies here

4. Identify the error in this global optimization attempt:

int sum = 0;
for (int i = 0; i < n; i++) {
  int x = i * 2;
}
sum += x;

medium

A. Variable x is used outside its scope

B. Loop condition is incorrect

C. Sum variable is not initialized

D. No optimization applied

Solution

1. Step 1: Check variable scope of x

   The variable x is declared inside the loop and cannot be accessed outside it.

2. Step 2: Analyze usage of x after the loop

   Using x after the loop causes a scope error, preventing optimization.

3. Final Answer:

   Variable x is used outside its scope -> Option A

4. Quick Check:

   Variable scope error = using inside variable outside loop [OK]

Hint: Check if variables are used only where declared [OK]

Common Mistakes:

• Ignoring variable scope rules
• Assuming sum is uninitialized
• Thinking loop condition is wrong

5. Given a program with multiple repeated calculations and unused variables scattered across functions, which combination of global optimization techniques would best improve performance?

hard

A. Dead code elimination and loop-invariant code motion

B. Constant folding and syntax checking

C. Register allocation and lexical analysis

D. Inlining and parsing

Solution

1. Step 1: Identify techniques for removing unused code and repeated calculations

   Dead code elimination removes unused variables; loop-invariant code motion moves repeated calculations out of loops.

2. Step 2: Exclude unrelated compiler tasks

   Syntax checking, lexical analysis, parsing, and register allocation are not global optimizations for code improvement.

3. Final Answer:

   Dead code elimination and loop-invariant code motion -> Option A

4. Quick Check:

   Remove unused + move repeated = dead code elimination + loop-invariant motion [OK]

Hint: Combine removing unused code and moving repeated code out [OK]

Common Mistakes:

• Confusing compiler phases with optimization
• Choosing unrelated techniques like parsing
• Ignoring the need for multiple optimizations