tqchen opened a new issue, #18872:
URL: https://github.com/apache/tvm/issues/18872
## Summary
Add virtual `VisitBufferDef`/`VisitBufferUse` hooks to `StmtVisitor`,
`StmtMutator`,
`StmtExprVisitor`, `StmtExprMutator`, and `TIRVisitorWithPath`. These allow
subclasses to customize buffer handling at definition vs use sites.
## Motivation
Currently, buffer field visiting (shape, strides, elem_offset) is duplicated
across
many visitor/mutator subclasses. Each one reimplements buffer field
traversal in
`VisitStmt_(const AllocBufferNode*)`, `VisitStmt_(const DeclBufferNode*)`,
etc.
More importantly, there is a semantic distinction between buffer
**definition** sites
(AllocBuffer, DeclBuffer, SBlock alloc_buffers) and buffer **use** sites
(BufferLoad,
BufferStore, SBlock reads/writes) that is not captured by the base visitor
API:
- At **definition** sites, buffer fields (shape, strides, elem_offset)
should be visited
because the defining scope owns those expressions.
- At **use** sites, buffer fields should NOT be re-visited, because the use
may occur
in a different scope where the buffer's shape variables are not defined.
Without this distinction, analyses like `UndefinedVars` can miss variables or
visit them in the wrong scope.
## Design
- `VisitBufferDef(buffer, alloc_data)` — called at definition sites. Visits
buffer
shape, strides, elem_offset. The `alloc_data` flag distinguishes:
- `true` (AllocBuffer, SBlock): data var is a new allocation (DEF)
- `false` (DeclBuffer): data var references existing allocation (USE)
- `VisitBufferUse(buffer)` — called at use sites (BufferLoad, BufferStore,
reads/writes).
Default is empty (no field re-visiting). Subclasses can override to track
data pointer uses.
- Buffer fields are visited at definition sites only. The base
`StmtMutator::VisitBufferDef`
also maintains a `buffer_remap_` map so mutated buffers propagate to use
sites automatically.
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