(The set of valid guesses in C is just a lot more restricted since they do not have `wrapping_offset`, and the model does not cover `restrict`.
That means they can actually feasibly give an algorithm for how to do the guessing.
They don't have to invoke scary terms like "angelic non-determinism", but the end result is the same -- and to me, the fact that it is equivalent to angelic non-determinism is what justifies this as a reasonable semantics.
-Presenting this as a concrete algorithm to pick a suitable provenance is then just a stylistic choice.
-Kudos go to Michael Sammler for opening my eyes to this interpretation of "user disambiguation".)
+Presenting this as a concrete algorithm to pick a suitable provenance is then just a stylistic choice.)
+Kudos go to Michael Sammler for opening my eyes to this interpretation of "user disambiguation", and arguing that angelic non-determinism might not be such a crazy idea after all.
What is left is the question of how to handle pointer-integer transmutation, and this is where the roads are forking.
PNVI-ae-udi explicitly says loading from a union field at integer type exposes the provenance of the pointer being loaded, if any.
I discussed above how my vision for Rust relates to the direction C is moving towards.
What does that mean for the design space of LLVM?
-Which changes need to be made to fix (potential) miscompilations in LLVM and to make it compatible with these ideas for C and/or Rust?
+Which changes would have to be made to fix (potential) miscompilations in LLVM and to make it compatible with these ideas for C and/or Rust?
Here's the list of open problems I am aware of:
-- LLVM needs to stop [removing `inttoptr(ptrtoint(_))`](https://github.com/llvm/llvm-project/issues/33896) and stop doing [replacement of `==`-equal pointers](https://github.com/llvm/llvm-project/issues/34577).
+- LLVM would have to to stop [removing `inttoptr(ptrtoint(_))`](https://github.com/llvm/llvm-project/issues/33896) and stop doing [replacement of `==`-equal pointers](https://github.com/llvm/llvm-project/issues/34577).
- As the first example shows, LLVM also needs to treat `ptrtoint` as a side-effecting operation that has to be kept around even when its result is unused. (Of course, as with everything I say here, there can be special cases where the old optimizations are still correct, but they need extra justification.)
- I think LLVM should also treat `inttoptr` as a side-effecting (and, in particular, non-deterministic) operation, as per the last example. However, this could possibly be avoided with a `noalias` model that specifically accounts for new kinds of provenance being synthesized by casts. (I am being vague here since I don't know what that provenance needs to look like.)
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