Summary

Optimized the excess cost computation in the Sierra gas analysis by replacing UnorderedHashMap and UnorderedHashSet with more efficient vector-based data structures. This change improves performance by using direct indexing instead of hash-based lookups when tracking statement costs.

Type of change

Please check one:

• Bug fix (fixes incorrect behavior)
• New feature
• Performance improvement
• Documentation change with concrete technical impact
• Style, wording, formatting, or typo-only change

Why is this change needed?

The current implementation uses hash-based data structures (UnorderedHashMap and UnorderedHashSet) for tracking excess costs and finalized statements during gas analysis. Since statements are already indexed sequentially, we can use more efficient vector-based structures with direct indexing, avoiding the overhead of hash computations and lookups.

What was the behavior or documentation before?

The code used UnorderedHashMap<StatementIdx, CostType> and UnorderedHashSet<StatementIdx> for tracking excess costs and finalized statements, requiring hash lookups for each access.

What is the behavior or documentation after?

The implementation now uses vec![None; self.program.statements.len()] and vec![false; self.program.statements.len()] with direct indexing, which provides faster access to the same data without changing the algorithm's behavior.

Additional context

This optimization is particularly beneficial for large programs with many statements, as it reduces the computational overhead during gas analysis without changing the functional behavior of the cost computation.