Available expressions analysis in Compiler Design - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding the purpose of available expressions analysis

What is the main goal of performing available expressions analysis in compiler design?

A To find expressions that have been computed and not modified on all paths to a program point

B To identify variables that are never used in the program

C To detect unreachable code segments in the program

D To determine the maximum number of loops nested in the program

💡 Hint

Think about expressions that can be reused without recomputation.

Available expressions analysis finds expressions that have already been computed and whose operands have not changed along all paths to a point, enabling optimization by reusing these expressions.

📋 Factual

intermediate

Data flow direction in available expressions analysis

In which direction is the data flow analysis performed for available expressions?

A Backward, from program end to start

B Forward, from program start to end

C Both forward and backward simultaneously

D Random order, depending on control flow

💡 Hint

Consider when expressions become available during execution.

Available expressions analysis is a forward data flow analysis because it tracks expressions computed as the program executes from start to end.

🔍 Analysis

advanced

Effect of assignment on available expressions

Given the statement x = y + z, which of the following expressions becomes unavailable immediately after this statement?

A All expressions containing <code>y</code> or <code>z</code>

B Only the expression <code>y + z</code>

C Any expression containing variable <code>x</code>

D No expressions become unavailable

💡 Hint

Think about how changing a variable affects expressions that use it.

Assigning to x changes its value, so any expression involving x may no longer be valid and thus becomes unavailable.

❓ Comparison

advanced

Difference between available expressions and reaching definitions

Which statement correctly distinguishes available expressions analysis from reaching definitions analysis?

A Available expressions are a backward analysis; reaching definitions are forward

B Available expressions track variable assignments; reaching definitions track expression computations

C Both analyses track the same information but use different algorithms

D Available expressions track computed expressions not invalidated; reaching definitions track where variables are assigned

💡 Hint

Consider what each analysis is trying to find about the program.

Available expressions analysis finds expressions computed and still valid; reaching definitions analysis finds where variables get their current values assigned.

❓ Reasoning

expert

Available expressions at a control flow join point

At a program point where two control flow paths join, how is the set of available expressions determined?

A By intersecting the sets of available expressions from both paths

B By taking the union of the sets of available expressions from both paths

C By taking the set from the path with more expressions available

D By discarding all expressions and starting fresh

💡 Hint

Think about which expressions are guaranteed to be available regardless of the path taken.

Only expressions available on all incoming paths are considered available at the join point, so the intersection of sets is used.