tqchen opened a new pull request, #20063:
URL: https://github.com/apache/tvm/pull/20063
This refactors TIRx buffers into ordinary `ir.Var` identities carrying an
immutable `BufferType`.
## Rationale
The old representation kept a standalone Buffer object, its logical metadata,
and a separate pointer-typed data Var. Generic Var substitution and
buffer-specific rebuilding could therefore let identity, metadata, and
pointer
type drift apart. In this change, `BufferType` is the single source of the
logical contract and `buffer_data(buffer)` is the explicit physical-pointer
projection; `DeclBuffer` records a view's binding.
## Simplification
- Generic Var scoping, substitution, undefined-variable analysis, and
identity
maps now apply directly to buffers.
- The pointer type is derived from `BufferType`, so the physical pointer and
buffer metadata cannot disagree.
- The common IR path no longer needs a second Buffer object, duplicate
constructor state, or a parallel buffer-only substitution mechanism.
- Metadata-changing transforms create a fresh typed Var and bind it
explicitly
at the replacing `AllocBuffer` or `DeclBuffer`.
Physical-root tracking remains deliberately local to the passes whose
correctness depends on allocation ownership:
1. Storage liveness/reuse attributes alias accesses to the owning allocation.
2. Pointer vector-type inference and rewriting aggregate evidence at that
root.
3. LowerTIRx cleanup projects aliases to the remapped physical allocation.
4. Thread-allreduce's deferred remapper replaces or removes the owning
allocation.
Each is a plain pass-local `Map<Var, Var>` flattened when a `DeclBuffer` is
visited. Parameters, `buffer_map`, and `AllocBuffer` seed roots; an alias to
an
unseen typed source is rejected rather than silently treated as a new root.
Simpler passes decode the one-step `buffer_data` projection locally.
## Migration guide
### C++
- Treat `BufferVar` as a checked view over an ordinary `Var`.
- Read logical metadata through `buffer->...`; use `buffer.var()` for
identity.
- Use `buffer.data()` or `builtin::buffer_data()` only when a physical
pointer
expression is required.
- To change metadata, rebuild `BufferType`, create a fresh Var, and bind it
at
the replacement definition site.
- A transformed `DeclBuffer` replaces its superseded declaration
consistently;
it must not leave a stale declaration beside the new binding.
### Python
- Buffer constructors return `tvm.ir.Var`; `.ty` contains `BufferType`.
- Use `tvm.tirx.is_buffer_var(value)` for runtime discrimination.
- `tvm.tirx.Buffer` remains an import and annotation compatibility alias for
`tvm.ir.Var`, so `isinstance(value, Buffer)` matches every Var.
- Importing `tvm.tirx` installs the legacy metadata properties on Var.
Non-buffer Vars raise `AttributeError`; buffer `.dtype` keeps its
historical
`DataType` result.
## Behavior preservation
The behavior-preserving follow-up restores established LowerTIRx,
FlattenBuffer, BF16, alias-lifetime, and declaration-replacement behavior
while
keeping ownership logic pass-local.
The final focused correction completes typed-buffer integration at structural
comparison, retyping, specialization, annotation, external-output, access
detection, projection lowering, printer, and target-codegen boundaries. It
also preserves the physical source handle type for declared aliases and
retains allocation-backed versus parameter-backed identity where lowering
requires that distinction.
## Validation
- Debug build with LLVM 18.1.8 and CUDA: passed.
- Affected 16-file suite: **318 passed, 1 xpassed, 7 environment-version
failures**. The seven failures occur in NumPy 2.3.5 test-data conversion
after LLVM compilation succeeds.
- Complete TIR and Relax specialization files: **12 passed**.
- Isolated schedule-state regression: **1 passed**.
- H200 paged-attention float32 prefill/decode nvcc regression: **1 passed**.
- Full unfiltered Python suite:
**10,170 passed, 2,699 skipped, 57 xfailed, 6 xpassed, 848 failed, 74
errors**. The remaining failures and errors were reproduced and classified
as local CUDA/NVRTC header, dependency-version, optional-build,
platform/tooling, base, or cross-test-global-state outcomes; no remaining
task-source regression was identified.
- Repository-pinned formatting, all pre-commit hooks, and `git diff --check`:
passed.
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