add evaluateFunctionExit for backward analyzer in monotone-analyzer

[HerrCai0907]

For backward analyzer, it is helpful to have a function to init state in the "entry point" (exit block).

[tlively]

Makes sense, but would it be possible to add some usage somewhere to avoid this getting deleted as dead code in the future?

[HerrCai0907]

I am writing our own pass to analyze the opcode between local.get and corresponding really uses (ignore block / if / loop...). It needs to handle uses as return value from operand stack which needs this functional.
In current binaryen, I can only find LivenessTransferFunction is backward analysis but it does not need this function.

[tlively]

Would you be interested in upstreaming the pass you're writing? If not, and you're maintaining downstream patches, what's the benefit of having this function upstream?

[HerrCai0907]

Would you be interested in upstreaming the pass you're writing?

I am not sure the attitude of the bianryen community to frontend language specific pass. I guess it only welcomes the common part.

what's the benefit of having this function upstream?

To make the lattice based analysis framework more complete. If it is not needed, feel free to close this PR.

[tlively]

There is some precedent for having frontend-specific passes in Binaryen. We have J2CLOpts.cpp, which is specific to the j2wasm compiler, for example. We could consider adding more frontend-specific passes on a case-by-case basis. This would have the benefit to you of making sure your pass isn't broken if we refactor the static analysis framework and would also make sure that we have test coverage for the new method in this PR.

Alternatively we can just land this PR as-is, but be aware that future refactors might break your downstream pass unexpectedly. This isn't meant to be a stable, external-facing API.