Avoid lossy ptr-int transmutes by using AtomicPtr #19
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saethlin
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This repo contains a lot of copy-paste from
futures-timer, so this PR is almost a copy-paste of a PR to that repo: async-rs/futures-timer#66This project looks pretty inactive, but it is still used very widely by the ecosystem and Miri detects UB in it that looks unambiguously bad to me, so that's why I'm submitting a patch for it.
Rust doesn't have a formal memory model yet, but as far as we can tell it isn't sound to round-trip a pointer through an integer via transmutes in a compiler which does provenance-based optimizations (which LLVM and basically all modern compilers currently do). The fix here is pretty easy: we store an AtomicPtr instead of an AtomicUsize and we create our sentinel values using the wrapping_ pointer methods.
This PR is very similar to rust-lang/rust#95621.