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A fundamental principle of LuminAIR is its reliance on ahead-of-time (AOT) compilation. By pushing all computations to compile time, LuminAIR eliminates runtime overhead, ensuring that every operation in the computational graph is static and optimized before execution. When you write an expression like x + y in LuminAIR, no computation happens immediately. Instead:
  • The operation is recorded in a directed acyclic computation graph.
  • Actual computation occurs only when graph.gen_trace() is executed.
This approach, akin to lazy execution, allows LuminAIR to treat entire ML models as static computation graphs.

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Why AOT Compilation?

By fully representing ML models as static computation graphs, compilers have global knowledge of the entire model. This allows for:
  1. Advanced Optimizations: Compilers can perform tasks like operator fusion, backend-specific optimizations, and linking operations to their AIR equivalents.
  2. Separation of Concerns: All complexity is pushed to compile time, leaving runtime execution lightweight and efficient.

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How LuminAIR Compilers Work

Compilers in LuminAIR are modular and stackable, meaning multiple compilers can be applied sequentially to transform the computation graph. Each compiler focuses on a specific optimization task.

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Default Compilers Provided by LuminAIR

  1. GenericCompiler
    • Developed by Luminal, it applies backend-agnostic optimizations.
    • Includes techniques like Common Subexpression Elimination (CSE). to eliminate redundant computations.
    • Should always run before any specialized compilers.
  2. StwoCompiler
    • A specialized compiler designed for proving computational graphs using the Stwo prover.
    • Replaces operations in the graph with their equivalent components in the AIR.
StwoCompiler currently includes PrimitiveCompiler. It maps primitive operators (e.g., Add, Mul) to their corresponding AIR components. 
pub type StwoCompiler = (op::prim::PrimitiveCompiler,);
In the future, StwoCompiler will include additional sub-compilers, such as FuseOpCompiler, focuses on fusing multiple primitive operations into optimized composite operators.

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Customizing Compilers for Specific Use Cases

LuminAIR supports custom compilers, designed by users, that can be stacked alongside default ones to address specific use cases. 
cx.compile(<(GenericCompiler, MyCustomCompiler, StwoCompiler)>::default(), &mut e);
Here:
  • GenericCompiler applies general optimizations.
  • MyCustomCompiler implements user-defined transformations for a specific task.
  • StwoCompiler prepares the graph for proof generation using the Stwo prover.
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