Check for terminal symbol data usage in any reduce action

[ehwan]

Use empty stack instead of terminal symbol stack in the parser data stack, if certain terminal symbol's data was not used in any reduce action.

[gemini-code-assist]

Summary of Changes

Hello @ehwan, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request implements a significant optimization in how the parser handles terminal symbol data. Previously, data for all terminal symbols was pushed onto the parser's data stack, regardless of whether it was actually used in a subsequent reduce action. This change introduces a mechanism to detect unused terminal data and, in such cases, pushes an Empty tag onto the stack instead. This reduces memory overhead and improves performance by avoiding unnecessary data allocations and manipulations, particularly in generated parser code.

Highlights

• Optimized Terminal Data Handling: Introduced a data_used flag for terminal classes to track whether their associated data is consumed in any reduce action, preventing unnecessary data pushes.
• Conditional Data Pushing: The parser now conditionally pushes terminal data onto the stack; if data_used is false, an Empty tag is pushed instead of the actual terminal data, reducing memory overhead.
• Refined Parser Generation: Updated the grammar processing and parser generation logic to correctly determine and apply the data_used flag, leading to more efficient data stack management in generated parsers.
• Reduced Stack Operations: Numerous changes in generated parser files reflect this optimization by replacing terminal data pushes with Empty tags and removing corresponding data truncations.

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[gemini-code-assist]

Code Review

This pull request introduces a valuable optimization by avoiding pushing terminal symbol data to the parser stack when it's not utilized in any reduce actions. This is achieved by adding a data_used flag to TerminalClassDefinition, which is calculated by inspecting all reduce actions. The logic appears sound and is correctly applied to control the data pushing behavior during shift operations. The changes are well-implemented, and the resulting modifications in the generated parser code are consistent with this optimization. I have one minor suggestion to fix a typo in a comment.