[Bugfix] Restrict CopyOnWrite to _type_final #17132
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Prior to this commit, the `TVM_DEFINE_OBJECT_REF_COW_METHOD` could be used in any `ObjectRef` subclass to provide a `CopyOnWrite` method. However, the implementation of this method method was invalid if the object's `ContainerType` could itself be subclassed. In that case, using `obj.CopyOnWrite()` when the object contains a subclass, and when a copy is required, would silently convert `obj` to instead contain a base class. This commit adds a `static_assert`, to the `TVM_DEFINE_OBJECT_REF_COW_METHOD` macro, preventing the macro from being used in classes that would have incorrect usage. Compilation with this change found two classes, `relax::Var` and `relax::BindingBlock` that were susceptible to this error, and the macro has been removed from these classes. For backwards-compatibility, the `CopyOnWrite` function for these two classes is provided explicitly.
tqchen
approved these changes
Jul 2, 2024
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Prior to this commit, the
TVM_DEFINE_OBJECT_REF_COW_METHODcould be used in anyObjectRefsubclass to provide aCopyOnWritemethod. However, the implementation of this method method was invalid if the object'sContainerTypecould itself be subclassed. In that case, usingobj.CopyOnWrite()when the object contains a subclass, and when a copy is required, would silently convertobjto instead contain a base class.This commit adds a
static_assert, to theTVM_DEFINE_OBJECT_REF_COW_METHODmacro, preventing the macro from being used in classes that would have incorrect usage.Compilation with this change found two classes,
relax::Varandrelax::BindingBlock, that were susceptible to this error, and the macro has been removed from these classes. For backwards-compatibility, theCopyOnWritefunction for these two classes is provided explicitly.