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Make PlaceMention a non-mutating use. #110826

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merged 3 commits into from
May 4, 2023
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cjgillot
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Fixes #110781

r? @JakobDegen

I don't agree with your statement in #110781 (comment). I suggest that we start fixing PlaceContext to be accurate enough for optimizations to use it. This structure is very convenient to use in visitors, and we perhaps have an opportunity to make it less of a footgun.

@rustbot rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Apr 25, 2023
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rustbot commented Apr 25, 2023

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

@@ -1251,6 +1251,8 @@ pub enum NonMutatingUseContext {
UniqueBorrow,
/// AddressOf for *const pointer.
AddressOf,
/// PlaceMention statement.
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Might be worth adding a clarifying comment on why this is here, given that it used to be in the wrong category.

Inspect | Copy | Move | SharedBorrow | ShallowBorrow | UniqueBorrow | AddressOf
| Projection,
Inspect | Copy | Move | PlaceMention | SharedBorrow | ShallowBorrow | UniqueBorrow
| AddressOf | Projection,
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Looks like we're going from invariant to covariant here? If intentional, probably a behavior change that would need a types FCP?

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I'd consider this more of a bugfix for #104844, which is still on nightly.

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Ok, I'm going to cc @rust-lang/types here to get some eyes on this. From my understanding it's probably fine, but I'm definitely not a qualified reviewer

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being covariant is fine here 👍

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I suggest that we start fixing PlaceContext to be accurate enough for optimizations to use it.

I'd be very happy to do that if we can. My concern is just that PlaceMention is (presumably) the way it is because it makes sense elsewhere. If we start redefining it to be useful to opts, do we just move the bugs to borrowck?

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JakobDegen commented Apr 29, 2023

lgtm modulo the variance change

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RalfJung commented May 4, 2023

@JakobDegen

lgtm modulo the variance change

@lcnr

being covariant is fine here +1

@bors r=JakobDegen,lcnr

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bors commented May 4, 2023

📌 Commit 4ec76df has been approved by JakobDegen,lcnr

It is now in the queue for this repository.

@bors bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels May 4, 2023
bors added a commit to rust-lang-ci/rust that referenced this pull request May 4, 2023
…iaskrgr

Rollup of 8 pull requests

Successful merges:

 - rust-lang#108865 (Add a `sysroot` crate to represent the standard library crates)
 - rust-lang#110651 (libtest: include test output in junit xml reports)
 - rust-lang#110826 (Make PlaceMention a non-mutating use.)
 - rust-lang#110982 (Do not recurse into const generic args when resolving self lifetime elision.)
 - rust-lang#111009 (Add `ascii::Char` (ACP#179))
 - rust-lang#111100 (check array type of repeat exprs is wf)
 - rust-lang#111186 (Add `is_positive` method for signed non-zero integers.)
 - rust-lang#111201 (bootstrap: add .gitmodules to the sources)

Failed merges:

 - rust-lang#110954 (Reject borrows of projections in ConstProp.)

r? `@ghost`
`@rustbot` modify labels: rollup
@bors bors merged commit 0ac8ebd into rust-lang:master May 4, 2023
@rustbot rustbot added this to the 1.71.0 milestone May 4, 2023
@cjgillot cjgillot deleted the place-mention-use branch May 4, 2023 21:39
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UB: edition 2015/18 with -Zmir-opt-level=2: destructing tuple inside closure
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