8d2912ec00
Fix false-positive of redundant_clone and move to clippy::perf This PR introduces dataflow analysis to `redundant_clone` lint to filter out borrowed variables, which had been incorrectly detected. Depends on https://github.com/rust-lang/rust/pull/64207. changelog: Moved `redundant_clone` lint to `perf` group # What this lint catches ## `clone`/`to_owned` ```rust let s = String::new(); let t = s.clone(); ``` ```rust // MIR _1 = String::new(); _2 = &_1; _3 = clone(_2); // (*) ``` We can turn this `clone` call into a move if 1. `_2` is the sole borrow of `_1` at the statement `(*)` 2. `_1` is not used hereafter ## `Deref` + type-specific `to_owned` method ```rust let s = std::path::PathBuf::new(); let t = s.to_path_buf(); ``` ```rust // MIR _1 = PathBuf::new(); _2 = &1; _3 = call deref(_2); _4 = _3; // Copies borrow StorageDead(_2); _5 = Path::to_path_buf(_4); // (*) ``` We can turn this `to_path_buf` call into a move if 1. `_3` `_4` are the sole borrow of `_1` at `(*)` 2. `_1` is not used hereafter # What this PR introduces 1. `MaybeStorageLive` that determines whether a local lives at a particular location 2. `PossibleBorrowerVisitor` that constructs [`TransitiveRelation`](https://doc.rust-lang.org/nightly/nightly-rustc/rustc_data_structures/transitive_relation/struct.TransitiveRelation.html) of possible borrows, e.g. visiting `_2 = &1; _3 = &_2:` will result in `_3 -> _2 -> _1` relation. Then `_3` and `_2` will be counted as possible borrowers of `_1` in the sole-borrow analysis above. |
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