Lunderberg opened a new pull request, #15923:
URL: https://github.com/apache/tvm/pull/15923
Prior to this commit, the `tvm::script::printer::AttrPrinter` class took the
attribute path as a `const ObjectPath&`. In both places where an `AttrPrinter`
is called, the temporary object `n_p->Attr("attrs")` is passed for this
argument. While binding a temporary object to a const reference can extend the
lifetime of the temporary, this requires the const reference to be in the same
scope as the temporary, and does not apply in this case (see [this
stackoverflow post](https://stackoverflow.com/a/2784304)). Therefore, this
reference is only valid through the construction of `AttrPrinter printer`, and
is invalid during its usage on the following line.
This dangling reference has caused segfaults in CI for unrelated changes
([example](https://ci.tlcpack.ai/blue/organizations/jenkins/tvm-unity/detail/PR-15904/3/pipeline)),
and can be reproduced with the following test case.
```python
import pytest
from tvm.script import relax as R
@pytest.mark.parametrize("iter", range(10000))
def test_argmax_without_specified_axis(iter):
@R.function
def func(x: R.Tensor((1, 2, 3, 4), "float32")):
return R.argmax(x)
func.script(show_meta=True)
```
This test case is not included in this commit, as the reproduction is not
consistent, with failure requiring on the order of 10k iterations to trigger.
In addition, reproduction was sensitive to the following conditions.
* The function being printed must contain at least one `relax::Call` node,
with an operation that has attributes.
* TVM must be built with optimization enabled. In gcc, the `-ftree-dse`
optimization, which is part of `-O1`, is required to trigger the bug.
* Python's default allocation must be used. If `PYTHONMALLOC=malloc` is set
to instead use the system's `malloc`, the segfault was no longer triggered.
This commit updates `AttrPrinter` to accept the `ObjectPath` by value. With
the change applied, the above test ran 100k times without error.
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