tqchen opened a new pull request, #18874:
URL: https://github.com/apache/tvm/pull/18874
## Summary
Rename `LetStmtNode`/`LetStmt` to `BindNode`/`Bind` and remove the `body`
field.
The variable defined by `Bind(var, value)` is now visible in all subsequent
statements within the same enclosing scope, rather than being scoped to a
nested body.
This flattens deeply nested let-chains into sequential `SeqStmt([Bind(...),
Bind(...), ...])`,
making the IR easier to read, transform, and analyze.
## Key Changes
- **New `BindNode`**: `{var, value}` — no body field. Variable scope is the
enclosing
statement's body (For, IfThenElse, AllocBuffer, etc.)
- **ScopeStack pattern**: Passes that need scope-aware cleanup (ConvertSSA,
CSE,
tir_visitor_with_path) use `ScopeStack` instead of manual save/restore or
RAII wrappers
- **All passes migrated**: 89 files updated across codegen backends, TIR
transforms,
S-TIR transforms, analyses, TVMScript printer/parser/ir_builder
- **LetStmt aliases removed**: No backward-compat aliases remain
## Design
Since TIR enforces SSA (each var bound exactly once), most passes simply
insert into
a global `var_map_` on encountering `Bind` — no scope cleanup needed. For
the few passes
that do need scoped cleanup, `ScopeStack` provides clean RAII-based scope
management:
body-carrying statements push a new scope, `Bind` adds to the current scope,
and cleanup
happens automatically when the scope exits.
## Test plan
- [x] C++ cpptest: 235 passed
- [x] all-platform-minimal-test: 75 passed
- [x] tir-base: 269 passed
- [x] tir-analysis: 24 passed
- [x] test_tir_transform_convert_ssa: 13 passed
- [x] test_tir_transform_common_subexpr_elim: 8 passed
- [x] test_tir_transform_lower_tvm_builtin: 8 passed
- [x] test_tir_transform_simplify: 76 passed
- [x] test_tvmscript_roundtrip: 143 passed
- [x] test_target_codegen_llvm: 1 passed
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