gemini-code-assist[bot] commented on PR #18886:
URL: https://github.com/apache/tvm/pull/18886#issuecomment-4015021735
## Summary of Changes
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This pull request significantly revamps the Common Subexpression Elimination
(CSE) pass within the TIR (Tensor IR) framework. The core change introduces a
robust two-phase architecture, separating the analysis and planning of CSE
opportunities from their mechanical application. This new design aims to
improve the clarity, maintainability, and efficiency of the CSE pass by
eliminating complex cascade loops and enabling more precise control over
variable introduction and expression substitution.
### Highlights
* **Two-Phase Architecture**: Rewrote TIR Common Subexpression Elimination
(CSE) with a two-phase design: CSEPlanner (read-only visitor for plan
generation) and CSERewriter (mechanical mutator for applying changes).
* **Simplified Architecture**: Replaced interleaved analysis/mutation with
clean CSEPlanner and CSERewriter classes.
* **No Cascade Loop**: Implemented shallower-first processing with
representation propagation, eliminating the need for cascade loops in CSE
resolution.
* **Incremental DAG Construction**: Computed expression depth, children, and
consumed counts during a single bottom-up scan.
* **No Single-Use Bindings**: Added consumed count tracking to prevent
introducing CSE variables that would only be used once.
* **Unified Insertion**: Handled all insertion contexts uniformly via
VisitStmt and SeqStmt flattening.
* **API Changes**: Renamed CommonSubexprElimTIR to CommonSubexprElim,
removed enable_cse_tir and identify_equiv_terms parameters, and added T.bind as
a lowercase alias for T.Bind.
* **Code Refactoring**: Moved old CSE tools used by cache_index to
cache_index_helpers.{cc,h} and removed the unused arith.detect_common_subexpr
API.
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<details>
<summary><b>Changelog</b></summary>
* **include/tvm/tir/transform.h**
* The CommonSubexprElimTIR function was renamed to CommonSubexprElim.
* The enable_cse_tir and identify_equiv_terms parameters were removed
from the CommonSubexprElim function signature.
* The documentation for the CommonSubexprElim pass was updated to
reflect the use of Bind statements.
* **python/tvm/arith/__init__.py**
* The import of detect_common_subexpr was removed.
* **python/tvm/arith/pattern.py**
* The detect_common_subexpr function and its related PrimExpr import
were removed.
* **python/tvm/s_tir/backend/adreno/pipeline.py**
* The call to tir.transform.CommonSubexprElimTIR was updated to
tir.transform.CommonSubexprElim and its parameters were removed.
* The CSE pass is now conditionally appended based on
tir.disable_cse_tir.
* **python/tvm/s_tir/pipeline.py**
* The call to tir.transform.CommonSubexprElimTIR was updated to
tir.transform.CommonSubexprElim and its parameters were removed.
* The CSE pass is now conditionally appended based on
tir.disable_cse_tir.
* **python/tvm/script/ir_builder/tir/ir.py**
* A lowercase alias bind was added for Bind.
* The bind alias was added to the __all__ export list.
* **python/tvm/tir/transform/transform.py**
* The Python binding for CommonSubexprElimTIR was renamed to
CommonSubexprElim.
* The enable_cse_tir and identify_equiv_terms parameters were removed
from the Python function signature.
* **src/arith/detect_common_subexpr.cc**
* This file, containing the old DetectCommonSubExpr implementation, was
removed.
* **src/s_tir/schedule/primitive/cache_index.cc**
* The include path for common_subexpr_elim_tools.h was updated to
cache_index_helpers.h.
* **src/s_tir/schedule/primitive/cache_index_helpers.cc**
* A new file was added, implementing analysis tools and utility
functions for cache_index, extracted from the old common_subexpr_elim_tools.cc.
* **src/tir/ir/transform.cc**
* The tir.enable_equiv_terms_in_cse_tir pass configuration option was
removed.
* **src/tir/transform/common_subexpr_elim.cc**
* The entire implementation of the CSE pass was rewritten to a two-phase
architecture (CSEPlanner and CSERewriter).
* The CommonSubexprElimTIR pass was renamed to CommonSubexprElim and its
parameters were removed.
* Detailed documentation was added for the new architecture, eligibility
rules, and scope tree.
* **src/tir/transform/common_subexpr_elim.h**
* This header file, containing the old CommonSubexpressionEliminator
class, was removed.
* **src/tir/transform/common_subexpr_elim_tools.cc**
* This file, containing the old CSE analysis tools, was removed. Its
relevant parts were moved to cache_index_helpers.cc.
* **src/tir/transform/common_subexpr_elim_tools.h**
* The header file was renamed to
src/s_tir/schedule/primitive/cache_index_helpers.h and its contents were
adapted to serve as helpers for cache_index.
* Removed UsesVarName class, PrintComputationTable, MaybeValue,
PredicateIntroVarForComputation, and VectorMap utilities.
* Updated include paths for support/ordered_map.h.
* **tests/python/arith/test_arith_detect_cse.py**
* This test file was removed.
* **tests/python/tir-transform/test_tir_transform_common_subexpr_elim.py**
* Existing tests were updated to use the new CommonSubexprElim pass
without the removed parameters.
* New test cases were added covering basic multi-level CSE,
single-branch and both-branch if CSE, cascade CSE, no duplication scenarios,
deterministic output, CSE inside and across for loops, handling of BufferLoad
and Call expressions, nested if scope, multiple independent CSE candidates, if
condition CSE, and preventing single-use bindings.
</details>
<details>
<summary><b>Activity</b></summary>
* The pull request introduces 15 new test cases covering various scenarios
for the revamped CSE pass.
* The build process successfully passed.
* Ruff lint checks were successfully passed.
</details>
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