[NLL] Allow conflicting borrows of promoted length zero arrays #52834
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| // different promoteds - base case, disjoint | ||
| debug!("place_element_conflict: DISJOINT-PROMOTED"); | ||
| Overlap::Disjoint | ||
| } else if mir.promoted[p1.0].ignore_borrow_conflicts { |
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couldn't we just check for zero length array type here instead of infecting everything with that info?
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i'm with @oli-obk here: Lets see if that (presumably simpler) fix does the job here?
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I think I was concerned about performance thinking that it would need to be check way more than it actually is (which is once per promoted).
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…r=pnkfelix [NLL] Allow conflicting borrows of promoted length zero arrays This is currently overkill as there's no way to create two conflicting borrows of any promoted. It is possible that the following code might not fail due to const eval in the future (@oli-obk?). In which case either the array marked needs to not be promoted, or to be checked for conflicts ```rust static mut A: () = { let mut y = None; let z; let mut done_y = false; loop { let x = &mut [1]; // < this array if done_y { z = x; break; } y = Some(x); done_y = true; } some_const_fn(y, z); // some_const_fn expects that y to not alias z. }; ``` r? @pnkfelix @nikomatsakis closes rust-lang#52671 cc rust-lang#51823
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Rollup of 15 pull requests Successful merges: - #52793 (Add test for NLL: unexpected "free region `` does not outlive" error ) - #52799 (Use BitVector for global sets of AttrId) - #52809 (Add test for unexpected region for local data ReStatic) - #52834 ([NLL] Allow conflicting borrows of promoted length zero arrays) - #52835 (Fix Alias intra doc ICE) - #52854 (fix memrchr in miri) - #52899 (tests/ui: Add missing mips{64} ignores) - #52908 (Use SetLenOnDrop in Vec::truncate()) - #52915 (Don't count MIR locals as borrowed after StorageDead when finding locals live across a yield terminator) - #52926 (rustc: Trim down the `rust_2018_idioms` lint group) - #52930 (rustc_resolve: record single-segment extern crate import resolutions.) - #52939 (Make io::Read::read_to_end consider io::Take::limit) - #52942 (Another SmallVec.extend optimization) - #52947 (1.27 actually added the `armv5te-unknown-linux-musleabi` target) - #52954 (async can begin expressions) Failed merges: r? @ghost
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This is currently overkill as there's no way to create two conflicting borrows of any promoted.
It is possible that the following code might not fail due to const eval in the future (@oli-obk?). In which case either the array marked needs to not be promoted, or to be checked for conflicts
r? @pnkfelix @nikomatsakis
closes #52671
cc #51823