[tvm] branch unity updated: [Unity][TVMScript] Avoid dangling reference when printing Call attrs (#15923)

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masahi pushed a commit to branch unity
in repository https://gitbox.apache.org/repos/asf/tvm.git


The following commit(s) were added to refs/heads/unity by this push:
     new 559e94a0c8 [Unity][TVMScript] Avoid dangling reference when printing Call attrs (#15923)
559e94a0c8 is described below

commit 559e94a0c86909b5ba626ef59aa2ee6ccbdf3637
Author: Eric Lunderberg <Lu...@users.noreply.github.com>
AuthorDate: Thu Oct 12 20:19:49 2023 -0500

    [Unity][TVMScript] Avoid dangling reference when printing Call attrs (#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.
---
 src/script/printer/relax/call.cc | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/src/script/printer/relax/call.cc b/src/script/printer/relax/call.cc
index dc57ca3184..79461df083 100644
--- a/src/script/printer/relax/call.cc
+++ b/src/script/printer/relax/call.cc
@@ -27,9 +27,9 @@ namespace printer {
 
 class AttrPrinter : public tvm::AttrVisitor {
  public:
-  explicit AttrPrinter(const ObjectPath& p, const IRDocsifier& d, Array<String>* keys,
+  explicit AttrPrinter(ObjectPath p, const IRDocsifier& d, Array<String>* keys,
                        Array<ExprDoc>* values)
-      : p(p), d(d), keys(keys), values(values) {}
+      : p(std::move(p)), d(d), keys(keys), values(values) {}
 
   void Visit(const char* key, double* value) final {
     keys->push_back(key);
@@ -79,7 +79,7 @@ class AttrPrinter : public tvm::AttrVisitor {
     LOG(FATAL) << "TypeError: NDArray is not allowed in Attrs";
   }
 
-  const ObjectPath& p;
+  ObjectPath p;
   const IRDocsifier& d;
   Array<String>* keys;
   Array<ExprDoc>* values;