Live variable analysis in Compiler Design - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to identify variables that are live at a program point.

Compiler Design

live_vars = [1]

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

Aint()

Blist()

Cdict()

Dset()

Attempts:

3 left

💡 Hint

Common Mistakes

Using a list can cause duplicates and slower lookups.

Using a dictionary or integer is not suitable for storing variables.

Live variables are best tracked using a set to avoid duplicates and allow fast membership checks.

2fill in blank

medium

Complete the code to update live variables after processing a statement.

Compiler Design

live_vars = (live_vars - [1]) | [2]

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Adefs

Buses

Ckills

Dgen

Attempts:

3 left

💡 Hint

Common Mistakes

Removing used variables instead of defined variables.

Confusing gen and kill sets.

Variables defined (defs) in a statement are removed from live variables because they get new values, then union with used variables (uses).

3fill in blank

hard

Fix the error in the live variable update formula.

Compiler Design

live_in = (live_out - [1]) | [2]

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

Agen

Buses

Ckills

Ddefs

Attempts:

3 left

💡 Hint

Common Mistakes

Using '+' instead of '|' for set union.

Removing uses instead of defs.

The correct operator to combine sets is union (|), not addition (+), and remove defs before adding uses.

4fill in blank

hard

Fill both blanks to compute live variables at a program point.

Compiler Design

live_in = (live_out - [1]) | [2]

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

Adefs

Buses

Ckills

Dgen

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping defs and uses in the formula.

Using kills or gen incorrectly.

Live variables coming into a statement are those live after it, minus variables defined there, plus variables used there.

5fill in blank

hard

Fill all three blanks to create a dictionary of live variables for each program point.

Compiler Design

live_vars_map = {point: ([3] - [1]) | [2] for point, ([3]) in program_points.items()}

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Adefs

Buses

Clive_info

Dkills

Attempts:

3 left

💡 Hint

Common Mistakes

Using kills or d instead of defs or uses.

Not unpacking live_info correctly.

For each program point, remove defined variables (defs), add used variables (uses), and unpack live_info from the items.