XLA HLO Pass Framework

This folder provides the core components of the XLA HLO pass framework, which is responsible for optimizing and transforming HLO computations within XLA compiler.

Key APIs and Files

hlo_pass_interface.h

Defines the foundational classes for HLO passes:

• HloPassInterface: Abstract base class for all HLO passes.
• HloModulePass: Subclass for passes that operate on individual HloModules.

Provides core methods like Run, andRunOnChangedComputations that passes must implement to perform their transformations.

hlo_pass_fix.h

Introduces the HloPassFix template class. Allows running an HLO pass repeatedly until a fixed point is reached (no further changes occur in the HLO). Useful for passes that may trigger further optimizations when applied iteratively.

hlo_pass_pipeline.h

Defines the HloPassPipeline class. Organizes a sequence of HLO passes into a pipeline for sequential execution. Provides methods to add passes (AddPass) and invariant checkers (AddInvariantChecker) to the pipeline. Run method executes the entire pipeline on an HloModule.

Example Usage

// Create a pipeline
HloPassPipeline pipeline("my_pipeline");

// Add passes to the pipeline
pipeline.AddPass<SomeOptimizationPass>(/* pass arguments */);
pipeline.AddPass<HloPassFix<AnotherOptimizationPass>>(/* pass arguments */);

// Run the pipeline on an HloModule
HloModule module(/* ... */);
auto status = pipeline.Run(&module);

Important Considerations

When creating custom HLO passes, inherit from HloModulePass. Implement the required virtual methods (e.g., RunImpl) to define the pass's behavior. Utilize HloPassFix when your pass's transformations may trigger further optimizations upon repeated application. Construct HloPassPipelines to orchestrate the execution of multiple passes in a defined sequence.