[PATCH] D91583: [lld] Allow --export-dynamic to override --lto-whole-program-visibility

[Fangrui Song via Phabricator via llvm-commits]

MaskRay added a comment.

Hi, I am still learning the feature and I've just played a bit with the test. I've a couple of questions:

- The `--export-dynamic` usage in the test seems a bit confusing. Are the `VisibleToRegularObj` bits of these `_ZTV*` symbols the important matter and `--export-dynamic` is just an approach to make them true?
- If yes, I guess all these `--export-dynamic` can be replaced with `-u _ZTV1B -u _ZTV1C -u _ZTV1D` in all the RUN lines. `--export-dynamic` is preferred just due to its brevity. If that is the case, I think this deserves a comment considering its subtle interaction with `noexportdynamic`.
- When is devirtualization invalid? For example, if `_ZTV1D` is exported to the dynamic symbol table and a shared object inherits from class D and overrides the method?

If my last point is correct, I'd agree that we need something like a tri-state option. (I hope we can remove `--lto-whole-program-visibility` if possible)
`on/noexportdynamic` the value names do not capture the actual meaning. The `on` actually means: devirtualization is safe as long as the used `_ZTV*` symbols are not exported.


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https://reviews.llvm.org/D91583