JackWeiw commented on PR #16679:
URL: https://github.com/apache/tvm/pull/16679#issuecomment-1985227683
> I agree, it sounds like this is an issue where there's an insufficient
condition, rather than a missing rewrite rule. If the test case is run without
this PR, but providing the knowledge that `x > 0`, (`TestCase(tvm.te.min(0,
fld(x + 3, 4) * 4 - 1), 0, x>0)` in the unit tests), then it passes.
>
> There's a couple different ways that assumptions can be added to the
function.
>
> 1. Using the variable as a dynamic shape. This is already applied, but
isn't a strong enough assumption to perform the simplifications you want. In
your script, this would provide `m >= 0`, while the simplification requires `m
> 0`. Since TIR allows a zero-dimension axis, this is the correct default
behavior.
> 2. Adding `T.assume(m > 0)` to the function. Using `T.assume` provides
additional information, but has undefined behavior if the assumption is
violated.
> 3. Adding `T.Assert(m > 0, "Some error message here")` to the function.
Using `T.Assert` performs a runtime validation, raising an exception if the
assertion is violated. All compile-time simplifications after the `T.Assert`
may assume that the assumption holds.
>
> I'd recommend using `T.Assert`, and only falling back to the `T.assume` if
there are performance reasons to avoid the runtime validation.
Thanks for your suggestion! Yes without this PR, but add preconfition x>0
both TestCases in Min and Max are passed.
BTW, could please give me one more hint on how to add `T.Assert(m > 0, "Some
error message here")` automatically to all the function in an IRModule if there
are symbolic shapes ? I am not very familiar with writing a pass, your kindly
suggestion would help me a lot !
BTW, should i close this PR or should i keep the added testcase by adding
precondition` x>0` `TestCase(tvm.te.min(0, fld(x + 3, 4) * 4 - 1), 0, x > 0) `
and cancel the change in rewrite_simplify ?
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