Local optimization (peephole) in Compiler Design - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to identify a simple peephole optimization that removes redundant load instructions.

Compiler Design

if instruction == 'LOAD A' and next_instruction == '[1]':
    optimize_remove(next_instruction)

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

ALOAD A

BADD B

CSTORE A

DLOAD B

Attempts:

3 left

💡 Hint

Common Mistakes

Choosing a different instruction that does not match the first load.

Confusing STORE with LOAD instructions.

The peephole optimization removes a redundant 'LOAD A' instruction if it immediately follows another 'LOAD A'. This avoids loading the same value twice.

2fill in blank

medium

Complete the code to replace a multiplication by 2 with an addition, a common peephole optimization.

Compiler Design

if instruction == 'MUL [1] 2':
    replace_with('ADD [1] [1]')

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

Az

By

Cx

Da

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variables in the multiplication and addition.

Not replacing multiplication by 2 specifically.

Multiplying a variable by 2 can be optimized by adding the variable to itself. Here, 'x' is used as the variable.

3fill in blank

hard

Fix the error in the peephole optimization that incorrectly replaces 'SUB x 0' with 'ADD x 0'.

Compiler Design

if instruction == 'SUB [1] 0':
    replace_with('[2]')

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

ASUB

BNOP

CMOV

DADD

Attempts:

3 left

💡 Hint

Common Mistakes

Replacing subtraction by zero with addition by zero, which is unnecessary.

Not using a no-operation instruction.

Subtracting zero from a variable does nothing, so it can be replaced with a 'NOP' (no operation) instead of an addition.

4fill in blank

hard

Fill both blanks to optimize a sequence that loads a constant zero and then adds it to a variable.

Compiler Design

if instructions == ['LOAD 0', 'ADD [1]']:
    replace_with('[2]')

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

Ax

BNOP

CMOV

Dy

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to move or load the variable unnecessarily.

Not recognizing that adding zero is redundant.

Adding zero to a variable does nothing, so the entire sequence can be replaced with a no-operation (NOP).

5fill in blank

hard

Fill all three blanks to optimize a sequence that multiplies a variable by 1 and then stores it.

Compiler Design

if instructions == ['MUL [1] 1', 'STORE [2]']:
    replace_with('[3] [2]')

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

Ax

By

CMOV

DNOP

Attempts:

3 left

💡 Hint

Common Mistakes

Replacing multiplication by 1 with a no-operation, which skips necessary data movement.

Using the wrong variable names inconsistently.

Multiplying by 1 does not change the value, so the multiplication can be removed and replaced by a move (MOV) instruction before storing.