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Refactor move analysis subpath representation #147575

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Refactor move analysis subpath representation #147575

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@beepster4096 beepster4096 commented Oct 10, 2025 •
edited by rustbot
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Follow up to #147055

This PR does two things:

  1. Document/validate move analysis's assumptions about Subslice projections
  2. Decouple move paths from ProjectionElem, using a new enum MoveSubPath instead
    • This would be needed eventually when ProjectionElem::Deref is removed

I wanted to do even more abstraction, making MovePathLookup::find return an iterator to remove the special handling of subslices in borrowck, but that regressed diagnostics and just wasn't worth the complexity.

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rustbot commented Oct 10, 2025

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

This PR changes MIR

cc @oli-obk, @RalfJung, @JakobDegen, @vakaras

The rustc-dev-guide subtree was changed. If this PR only touches the dev guide consider submitting a PR directly to rust-lang/rustc-dev-guide otherwise thank you for updating the dev guide with your changes.

cc @BoxyUwU, @jieyouxu, @Kobzol, @tshepang

@rustbot rustbot added A-rustc-dev-guide Area: rustc-dev-guide 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 Oct 10, 2025
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rustbot commented Oct 10, 2025

r? @jdonszelmann

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RalfJung
RalfJung reviewed Oct 11, 2025
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compiler/rustc_middle/src/mir/syntax.rs
/// Otherwise `array[from..to]`.
///
/// This projection cannot have `ConstantIndex` or additional `Subslice` projections after it
/// before runtime MIR.
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Is this something that the MIR validation pass could check?

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bors commented Oct 11, 2025

☔ The latest upstream changes (presumably #147574) made this pull request unmergeable. Please resolve the merge conflicts.

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oli-obk commented Oct 11, 2025

Haven't reviewed the validation yet, but the main part lgtm and is an improvement in readability and maintainability

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