[TIR][Schedule]Generalize fuseReductionEpilogue to support arbitrary epilogue expressions

[kimm240]

Major Changes for Generalization

1. Pattern Matching Removal

Removed Items:

• EpilogueType enum (Bias, BiasReLU, Clipping)
• AnalyzeEpiloguePattern() function
• Pattern-specific branching logic

Current Approach:

• Directly process the entire epilogue expression without pattern matching

2. Store Entire Epilogue Expression

• Store the entire epilogue expression in epilogue_expression_
• Use the expression directly without pattern analysis

// Store the epilogue expression and reduction buffer load
epilogue_expression_ = inlined_store_->value;
reduction_buffer_load_ = loads[0];

3. Generalized Init Transformation

• Replace reduction buffer load with identity element (0)
• Apply to the entire expression to generate init value

InitSubstituter init_subst(inlined_buffer_, identity_elem);
PrimExpr init_epilogue = init_subst(epilogue_expression_);
// Simplify: 0 + C[vi, vj] -> C[vi, vj]

Examples:

• temp + C → 0 + C → C (simplify)
• max(temp + C, 0) → max(0 + C, 0) → max(C, 0)
• min(max(temp, lower), upper) → min(max(0, lower), upper)

4. Generalized Update Transformation

• Replace reduction buffer load with reduction update
• If parent is Add and the other operand is not a reduction buffer → treat as bias addend and remove
• Otherwise → apply expression as-is

class GeneralizedEpilogueApplier : public ExprMutator {
  // Replace reduction buffer load with reduction update
  // Automatically detect and remove bias addend in Add nodes
  // Automatically support other activation functions
};

Results and Verification

Existing Tests Pass

All existing tests pass, maintaining backward compatibility:

• test_fuse_reduction_epilogue_basic
• test_fuse_reduction_epilogue_fp32
• test_fuse_reduction_epilogue_numerical_correctness
• test_fuse_reduction_epilogue_multiple_epilogue
• test_matmul_bias_relu
• test_matmul_bias_relu_correctness_unified
• test_matmul_clipping
• test_matmul_clipping_correctness_unified
• Other commutative variants tests

Total: All 15 tests pass

[gemini-code-assist]

Summary of Changes

Hello @kimm240, 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 significantly refactors the fuseReductionEpilogue mechanism to support arbitrary epilogue expressions, moving away from a rigid pattern-matching approach. By storing the entire epilogue expression and introducing generalized transformation logic for both initialization and updates, the system becomes more flexible and extensible, capable of handling a wider range of post-reduction operations without needing explicit pattern definitions. This change improves the generality and maintainability of the code while ensuring backward compatibility with existing tests.

Highlights

• Pattern Matching Removal: The previous pattern-matching approach for epilogue types (Bias, BiasReLU, Clipping) has been entirely removed. This includes the deletion of the EpilogueType enum and the AnalyzeEpiloguePattern() function, simplifying the logic by directly processing the entire epilogue expression.
• Store Entire Epilogue Expression: The ReductionEpilogueFuser now stores the complete epilogue expression in epilogue_expression_ and identifies the specific reduction_buffer_load_ within it. This change eliminates the need for pattern-specific member variables and allows for a more generalized handling of post-reduction operations.
• Generalized Init Transformation: A new InitSubstituter class has been introduced to handle the initialization of the fused reduction block. It replaces the reduction buffer load within the full epilogue expression with an identity element (e.g., 0 for addition-based reductions), allowing for a generalized calculation of the initial value, which is then simplified.
• Generalized Update Transformation: The update logic now uses a GeneralizedEpilogueApplier within an UpdateSubstituter. This applier intelligently replaces the reduction buffer load with the reduction update. It also includes logic to automatically detect and remove bias addends if the reduction buffer load's parent is an Add node and the other operand is not a reduction buffer, supporting arbitrary activation functions.

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[gemini-code-assist]

Code Review

This pull request successfully generalizes the fuseReductionEpilogue primitive by removing the previous pattern-matching logic in favor of a more flexible, expression-based approach. This is a significant improvement that allows for handling arbitrary epilogue expressions. The implementation is well-aligned with the description. I have identified a couple of areas for improvement, mainly related to removing some dead code and simplifying a complex section of the implementation to enhance readability and maintainability. Overall, this is a great enhancement to the framework.

[kimm240]

@wrongtest-intellif In this PR, I implement general epilogue form. This idea is discussed in #18515.