[REFACTOR][IR] Cleanup attrs.h: drop NullValue, AttrsNodeReflAdapter, legacy BaseAttrsNode methods

[tqchen]

Overview

This PR cleans up include/tvm/ir/attrs.h by removing four deprecated abstractions:

1. NullValue<T>() sentinel helpers (replaced by ffi::Optional<T>)
2. AttrsNodeReflAdapter<DerivedType> shim template (Attrs structs now inherit BaseAttrsNode directly)
3. BaseAttrsNode::InitBySeq / InitByPackedArgs legacy initialization methods
4. DictAttrsNode::InitByPackedArgs override

It also migrates 9 pass-config classes from Attrs/AttrsNodeReflAdapter to ffi::Object, since they are pass configuration objects, not IR attributes.

Changes

Commit A — Replace NullValue() call sites ([REFACTOR][IR] Replace NullValue<T>() call sites with default construction)

• 11 source files: replace NullValue<T>() with T(), std::nullopt, or DataType::Void()
• manipulate.h/manipulate.cc: FlipAttrs::axis changed from Integer to ffi::Optional<int64_t>

Commit B — Drop NullValue, AttrsNodeReflAdapter, legacy BaseAttrsNode methods ([REFACTOR][IR] Drop NullValue declaration, AttrsNodeReflAdapter, BaseAttrsNode legacy methods)

• include/tvm/ir/attrs.h: removes NullValue<T>, InitBySeq, InitByPackedArgs, AttrsNodeReflAdapter<T>
• src/ir/attrs.cc: removes DictAttrsNode::InitByPackedArgs definition
• AttrsWithDefaultValues<T>() broadened to accept any ffi::ObjectRef subtype (needed for Commit D)
• Removes unused includes: reflection/accessor.h, <functional>, <vector>

Commit C — Subclass BaseAttrsNode directly ([REFACTOR][IR] Subclass BaseAttrsNode directly, drop AttrsNodeReflAdapter)

• 17 attrs headers in include/tvm/relax/attrs/ + include/tvm/target/virtual_device.h
• All struct FooAttrs : public AttrsNodeReflAdapter<FooAttrs> → struct FooAttrs : public BaseAttrsNode

Commit D — Migrate pass-config classes to ffi::Object ([REFACTOR] Migrate pass-config classes to subclass ffi::Object)

• 9 pass-config classes in src/s_tir/, src/tirx/, src/relax/backend/contrib/
• XConfigNode : public ffi::Object (was AttrsNodeReflAdapter<XConfigNode>)
• XConfig : public ffi::ObjectRef (was Attrs)
• Python bindings updated: 7 classes changed from _ir.Attrs to _ffi.Object

Design Decisions

AttrFieldInfo / OpNode::arguments kept: Pre-flight check revealed GetArgStructInfo() in op_common.h and op_common.cc actively reads op->arguments (names, counts). These were not dead metadata — deleting them would break Relax op argument validation. They are kept as-is.

Commit E (trim attrs.h includes) reduced in scope: Removing structural_equal.h, structural_hash.h, and <unordered_map> from attrs.h caused 47 downstream files to fail compilation. Rather than adding explicit includes to 47 files, only clearly-unused includes (reflection/accessor.h, <functional>, <vector>) were removed in Commit B.

Testing

• Build: clean compile with -DUSE_CUDA=OFF -DUSE_LLVM=ON
• Tests passing:
  • tests/python/ir/ (93 passed)
  • tests/python/relax/test_analysis.py, test_blockbuilder_core.py, test_op_manipulate.py, test_transform.py (209 passed)
  • tests/python/s_tir/transform/test_s_tir_transform_loop_partition.py, test_s_tir_transform_unify_thread_binding.py (30 passed)
  • tests/python/tirx-transform/test_tir_transform_unroll_loop.py, test_tir_transform_simplify.py, test_tir_transform_remove_no_op.py (108 passed, 6 xfailed)
• Pre-existing failures (unrelated to this PR): test_s_tir_transform_lower_opaque_block, test_s_tir_transform_compact_buffer_region::TestLetBinding::test_compact, test_tir_transform_vectorize::test_vectorize_llvm_pure_intrin_fail

[gemini-code-assist]

Code Review

This pull request refactors the attribute system by removing the AttrsNodeReflAdapter and the NullValue template, replacing them with BaseAttrsNode or ffi::Object inheritance and default constructors. It also updates the flip operator's axis attribute to be an optional int64_t. However, two critical issues were identified in src/relax/op/tensor/manipulate.cc where attrs->axis.value() is called unconditionally on the newly optional axis field, which will crash if the axis is omitted.