Lunderberg opened a new pull request, #14951:
URL: https://github.com/apache/tvm/pull/14951
Prior to this commit, any trivial let binding of `var1 = var2` is inlined.
However, buffer definitions are not updated, so this can result in dangling
`tir::Var` instances. This commit updates the `tir.Simplify` pass to keep
trivial let bindings if they are used as part of a buffer definition.
Ideally, the trivial `LetStmt` variable would be inlined into the buffer
definition as well as other expressions. However, because a buffer may be
implicitly declared, the first usage may be within a constrained context. If
that happens, the simplified shape/strides expression cannot be used to update
the buffer definition, as that simplification is not valid at all possible
usage points of the buffer.
```python
for i in range(n):
elem_offset = i
view = T.Buffer(1, data=buf, elem_offset = elem_offset)
if i == 0:
# First occurrence in TIR is here, where elem_offset would
# simplify to zero.
view[0] = 1
else:
# But the same buffer is used here, where elem_offset doesn't
# simplify to zero.
view[0] = 2
```
This will be resolvable after https://github.com/apache/tvm/pull/14778
lands, requiring all buffers to be declared with `DeclBuffer` prior to usage.
```python
for i in range(n):
elem_offset = i
# All variables used by the DeclBuffer are valid across the entire
# body of the DeclBuffer.
view = T.decl_buffer(1, data=buf, elem_offset = elem_offset)
if i == 0:
view[0] = 1
else:
view[0] = 2
```
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