Consolidation of Selective Build APIs for OSS

🚀 The feature, motivation and pitch

Currently, there are three ways a user can enable the selective build process:

0. Disable selective build and include all operators.
1. Specify a string list of operators.
2. Provide a YAML file to enumerate which operators and dtypes should be included.
3. Provide a exported model (pte) to tailor the executorch build to the operators and tensor dtypes used in the model.

Right now, these APIs are treated as mutually exclusive, but there are use cases where a mixture of methods would be desirable. It would be ideal if there was a clearer/default way to enable selective builds without exposing too much of the configuration burden onto a user.

Example Use Case

A user wants to run two different models, where the second model only contains one differing operator. The user could determine the complete union of operators used by the two models, and manually specify them using the list API, but it would be easier if they could simply pass in one of the models and augment the selected operator set with the single differing operator (i.e. use the model API in conjunction with the list API).

Alternatives

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Additional context

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RFC (Optional)

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Start with codegen/tools/gen_oplist.py, especially the current mutually exclusive input handling around lines 222-228. Review how the operator-list, YAML, and exported-model inputs are represented, then define acceptance cases for combining them and verify that selective builds include the union of the requested operators and dtypes.