wrongtest edited a comment on pull request #9482:
URL: https://github.com/apache/tvm/pull/9482#issuecomment-972538596
I have another three questions about the pass.
1. Since function calls are non-eligible, it seems to prevent many common
non-stateful builtin computations from being optimized, such as `tir.floordiv`,
`tir.shift_right`, `tir.likely`, `tir.log` and etc. TVM already have op
annotation like `PURE`:
https://github.com/apache/tvm/blob/main/include/tvm/tir/op_attr_types.h#L60-L67
what if to add an annotation type like `DETERMINISTIC` to mark the
function return same output on same input. It should be
safe to eliminate common calls if the call op is both pure and
deterministic.
2. Is the let binding semantic in tir explicitly what we want? Is the value
expr is specified to be evaluated at let scope entry? otherwise there may be no
reuse effect if let-binding allow the value expr get lazily expanded in let
body.
3. Is this possible for some complex (but common) expr to be lifted out of
control flow scope? eg
```python
if cond0:
tir.evaluate(complex_e) # slow path
else:
if cond2:
tir.evaluate(complex_e) # slow path
else:
... # general fast path
```
after CSE maybe comes to
```python
x = tir.Var("int32")
with tir.let(x, complex_e): # always evaluate slow path
if cond0:
tir.evaluate(x)
else:
if cond2:
tir.evaluate(x)
else:
... # general fast path
```
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