Removing Owned DecoratorStorage Variant: 0xMiden Discussion

The ultimate goal of the ongoing refactoring series in 0xMiden's Miden VM project is to remove decorator_store from the nodes. This discussion delves into the complexities and challenges involved in achieving this objective, particularly focusing on the elimination of the Owned variant of DecoratorStorage. Let's explore the key scenarios where the Owned variant is currently necessary and the proposed path forward for its eventual removal.

The Role of Owned Decorators

The Owned variant of DecoratorStorage plays a crucial role in several key scenarios within the Miden VM architecture. Understanding these scenarios is essential to grasping the challenges associated with its removal:

1. Deserialization: When nodes are retrieved from disk or storage, they often come back with Owned decorators. This is a fundamental aspect of how the system currently handles persistent data.
2. Round-trip conversions: Transformations between Node and Builder objects, which are necessary for forest operations like merging and rewriting, rely on the Owned variant. These conversions are integral to the dynamic manipulation of the VM's structure.
3. Testing: Creating nodes for testing purposes often requires the ability to instantiate them without the overhead of a full forest setup. The Owned variant provides a convenient way to achieve this.

Efforts have been made to eliminate Owned from functions like add_to_forest(), but these attempts haven't addressed the core issues presented by the three scenarios outlined above. Therefore, a more comprehensive strategy is needed.

The Larger Refactoring Context

The removal of the Owned variant is part of a larger refactoring effort tracked under issue #1497. This broader initiative aims to eliminate the need for DecoratorStore in nodes altogether by storing all decorator-related information in a centralized arena. This approach promises to streamline the architecture and improve performance.

This comprehensive refactoring involves several key steps, each building upon the previous one. The complexity of this process highlights the intricate nature of the Miden VM and the careful planning required to make significant architectural changes.

The Path Forward: A Multi-Step Process

The path to removing the Owned variant and ultimately decorator_store from nodes is a multi-step process. Each step addresses specific challenges and lays the groundwork for the subsequent ones. Here's a breakdown of the proposed path forward:

1. Complete the PR series to hoist decorators to the forest: This step involves moving decorator management to the forest level, which is a prerequisite for further refactoring. This stage is crucial for centralizing decorator handling and reducing redundancy.
2. Implement DebugInfo struct (#1776): The DebugInfo struct will provide a standardized way to handle debugging information, which is essential for maintaining the VM's functionality and testability as it evolves. This is not just about removing a component; it's about improving the overall architecture and maintainability of the system.
3. Break backwards-compatible serialization to split decorator info (#1580): This step involves modifying the serialization format to separate decorator information, which will enable more efficient storage and retrieval. While breaking backwards compatibility is a significant decision, it's deemed necessary to achieve the long-term goals of the refactoring.
4. Rewrite the assembler's recursive descent, and refactor to fully commit to decorator info (#1497): This final step involves a major overhaul of the assembler's internal workings to fully leverage the new decorator information architecture. This will not only remove decorator_store from nodes but also potentially improve the assembler's performance and maintainability.

This phased approach allows for careful testing and validation at each stage, minimizing the risk of introducing regressions or instability. It also provides opportunities to learn and adapt the plan as new information becomes available.

Conclusion: A Phased Approach to Architectural Improvement

Removing the Owned variant of DecoratorStorage and ultimately decorator_store from nodes in 0xMiden's Miden VM is a significant undertaking. It's not a simple one-step process but rather a carefully planned series of steps that address various aspects of the VM's architecture. The need for the Owned variant in deserialization, round-trip conversions, and testing necessitates a phased approach to ensure a smooth transition and maintain the VM's stability and functionality.

The multi-step path forward, encompassing decorator hoisting, DebugInfo implementation, serialization changes, and assembler rewriting, demonstrates the commitment to long-term architectural improvement. While the goal is clear – to eliminate decorator_store from nodes – the journey is methodical and deliberate. This approach reflects a deep understanding of the system's intricacies and a dedication to building a robust and efficient virtual machine.

This phased approach highlights the importance of incremental improvements in complex software systems. By breaking down a large goal into smaller, manageable steps, the Miden VM team can ensure that each change is thoroughly tested and validated before moving on to the next. This reduces the risk of introducing bugs and allows for greater flexibility in adapting to new requirements or challenges.

Ultimately, the removal of the Owned variant is not just about simplifying the codebase; it's about enhancing the overall architecture, performance, and maintainability of the Miden VM. This commitment to continuous improvement is a hallmark of a well-designed and well-managed software project.

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