Document behavior of MaybeLiveLocals regarding enums and field-senstivity
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tmiasko
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Oct 5, 2021
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@bors r=oli-obk,tmiasko rollup |
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📌 Commit 9f9f7f6 has been approved by |
Manishearth
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…um, r=oli-obk,tmiasko Document behavior of `MaybeLiveLocals` regarding enums and field-senstivity This arose from a [discussion on Zulip](https://rust-lang.zulipchat.com/#narrow/stream/189540-t-compiler.2Fwg-mir-opt/topic/MaybeLiveLocals.20and.20Discriminants) where a new contributor attempted to implement a dead-store elimination pass using this analysis. They ran into a nasty hack around `SetDiscriminant` the effect of which is to lets handle assignments of literals to enum-typed locals (e.g. `x = Some(4)`) correctly. This took me a while to figure out. Document this oddity, so the next person will have an easier time, and add a test to enshrine the current behavior. r? `@tmiasko`
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…arth Rollup of 10 pull requests Successful merges: - rust-lang#88706 (Normalize associated type projections when checking return type of main) - rust-lang#88828 (Use `libc::sigaction()` instead of `sys::signal()` to prevent a deadlock) - rust-lang#88871 (Fix suggestion for nested struct patterns) - rust-lang#89317 (Move generic error message to separate branches) - rust-lang#89351 (for signed wrapping remainder, do not compare lhs with MIN) - rust-lang#89442 (Add check for duplicated doc aliases) - rust-lang#89502 (Fix Lower/UpperExp formatting for integers and precision zero) - rust-lang#89523 (Make `proc_macro_derive_resolution_fallback` a future-breakage lint) - rust-lang#89532 (Document behavior of `MaybeLiveLocals` regarding enums and field-senstivity) - rust-lang#89546 (Make an initial guess for metadata size to reduce buffer resizes) Failed merges: r? `@ghost` `@rustbot` modify labels: rollup
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This arose from a discussion on Zulip where a new contributor attempted to implement a dead-store elimination pass using this analysis. They ran into a nasty hack around
SetDiscriminant, which lets us handle assignments of literals to enum-typed locals (e.g.x = Some(4)) correctly. This took me a while to figure out.Document this oddity, so the next person will have an easier time, and add a test to enshrine the current behavior.
r? @tmiasko