MIR move elimination [4/6]: MoveElimination by Amanieu · Pull Request #163338 · rust-lang/rust

Amanieu · 2026-09-25T15:42:37Z

This PR implements the MoveElimination pass from rust-lang/rfcs#3943.

This pass uses the analysis results from PreciseLiveness to unify locals that are related by an assignment. This also includes an alias-fixup pass which is needed because some rvalues don't allow sources to overlap with the destination place.

The pass is only enabled under -Zmir-move-elimination. This flag also disables DestinationPropagation, which is superseded by the new pass.

r? tmiasko

Amanieu · 2026-09-25T16:06:39Z

LLM disclosure: LLMs were used to generate the boilerplate for the MIR tests, but each test was manually reviewed and adjusted before committing. LLMs were also used to audit this pass against the rest of the compiler MIR transforms and Miri semantics.

rustbot · 2026-10-08T23:26:44Z

This PR changes MIR

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

Some changes occurred in compiler/rustc_attr_parsing

cc @jdonszelmann, @JonathanBrouwer

Some changes occurred in compiler/rustc_attr_ir

cc @jdonszelmann, @JonathanBrouwer

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

This PR changes rustc_public

cc @oli-obk, @celinval, @ouz-a, @makai410

Amanieu · 2026-10-10T17:59:33Z

Rebased on top of main which now contains #163337. This PR now only has the commits related to the main MoveElimination pass.

…ination, r=tmiasko MIR move elimination [4/6]: MoveElimination Depends on rust-lang#163336 and rust-lang#163337 This PR implements the `MoveElimination` pass from rust-lang/rfcs#3943. This pass uses the analysis results from `PreciseLiveness` to unify locals that are related by an assignment. This also includes an alias-fixup pass which is needed because some rvalues don't allow sources to overlap with the destination place. The pass is only enabled under `-Zmir-move-elimination`. This flag also disables `DestinationPropagation`, which is superseded by the new pass. r? tmiasko

…uwer Rollup of 15 pull requests Successful merges: - #163664 (Add new `RUSTC_BOOTSTRAP=-allow-unstable-compiler-flags` mode for testing stable compiler behavior in UI tests) - #163104 ([debuginfo] Emit `usize` and `isize` as typedefs) - #163338 (MIR move elimination [4/6]: MoveElimination) - #163701 (add ReadDir::dir to get the directory handle of the underlying directory) - #164488 (Don't try to skip anything in `Skip::advance_by(0)`) - #164611 (Improve bit permutation codegen) - #164612 (std: Combine `is_powerpc64_feature_detected` into `is_powerpc_feature_detected`) - #148842 (Avoid incorrect lifetime suggestion involving `sym::anon`) - #162668 (document that `!` does bitwise and logical negation) - #164264 (lint: suggest `fXX::is_nan` for unsuffixed NaN comparisons) - #164509 (layout invariant: turn delayed bug back into proper assertion) - #164540 (Minor optimizations around macro parsing) - #164594 (rustdoc: Correctly handle inner `deprecated` attribute on modules) - #164595 (Allow attributes in function trait parameters) - #164629 (arch::breakpoint: avoid confusing 'equivalent' terminology)

Amanieu · 2026-10-20T14:36:18Z

Found an issue with invalid projections.

@bors r-

rust-bors · 2026-10-20T14:36:24Z

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Amanieu · 2026-10-20T19:25:55Z

This is a relatively minor issue that was only reachable in custom MIR, but essentially I had to extend the SIMD exclusion to also cover scalable vectors and DynMetadata, all of which are ADTs that don't allow projections into their fields.

tmiasko · 2026-10-20T21:27:52Z

@bors r+

rust-bors · 2026-10-20T21:27:55Z

📌 Commit a1af1ad has been approved by tmiasko

It is now in the queue for this repository.

…ination, r=tmiasko MIR move elimination [4/6]: MoveElimination Depends on rust-lang#163336 and rust-lang#163337 This PR implements the `MoveElimination` pass from rust-lang/rfcs#3943. This pass uses the analysis results from `PreciseLiveness` to unify locals that are related by an assignment. This also includes an alias-fixup pass which is needed because some rvalues don't allow sources to overlap with the destination place. The pass is only enabled under `-Zmir-move-elimination`. This flag also disables `DestinationPropagation`, which is superseded by the new pass. r? tmiasko

Rollup of 5 pull requests Successful merges: - #164672 (Bump `rustls-webpki` to 0.103.16 and `webpki-roots` to 1.0.10) - #163575 (core: Add examples and assembly tests for `abort_immediate`) - #163338 (MIR move elimination [4/6]: MoveElimination) - #163180 (Add more documentation for `chroot`, including an example and a manpage link) - #164638 (Make mir-opt blessing work again)

Rollup merge of #163338 - Amanieu:move-elimination/move-elimination, r=tmiasko MIR move elimination [4/6]: MoveElimination Depends on #163336 and #163337 This PR implements the `MoveElimination` pass from rust-lang/rfcs#3943. This pass uses the analysis results from `PreciseLiveness` to unify locals that are related by an assignment. This also includes an alias-fixup pass which is needed because some rvalues don't allow sources to overlap with the destination place. The pass is only enabled under `-Zmir-move-elimination`. This flag also disables `DestinationPropagation`, which is superseded by the new pass. r? tmiasko

Rollup of 5 pull requests Successful merges: - rust-lang/rust#164672 (Bump `rustls-webpki` to 0.103.16 and `webpki-roots` to 1.0.10) - rust-lang/rust#163575 (core: Add examples and assembly tests for `abort_immediate`) - rust-lang/rust#163338 (MIR move elimination [4/6]: MoveElimination) - rust-lang/rust#163180 (Add more documentation for `chroot`, including an example and a manpage link) - rust-lang/rust#164638 (Make mir-opt blessing work again)

…econstruction, r=tmiasko MIR move elimination [5/6]: Storage reconstruction Depends on rust-lang#163338 This PR extends the `MoveElimination` pass from rust-lang/rfcs#3943 to reconstruct `StorageLive`/`StorageDead` statements for all locals by using the liveness information collected by `PreciseLiveness`. r? tmiasko

Rollup merge of #163339 - Amanieu:move-elimination/storage-reconstruction, r=tmiasko MIR move elimination [5/6]: Storage reconstruction Depends on #163338 This PR extends the `MoveElimination` pass from rust-lang/rfcs#3943 to reconstruct `StorageLive`/`StorageDead` statements for all locals by using the liveness information collected by `PreciseLiveness`. r? tmiasko

rustbot assigned tmiasko Sep 25, 2026

Amanieu mentioned this pull request Sep 25, 2026

Implement RFC 3943: MIR move elimination #157943

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MIR move elimination [5/6]: Storage reconstruction #163339

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MIR move elimination rust-lang/goals#396

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MIR move elimination [1/6]: MIR preparation #163335

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Add merge yields pass #162429

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tmiasko reviewed Oct 12, 2026

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Comment thread compiler/rustc_mir_transform/src/move_elimination.rs Resolved

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Comment thread compiler/rustc_mir_transform/src/move_elimination.rs Resolved

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Comment thread compiler/rustc_mir_transform/src/move_elimination.rs Resolved

Amanieu force-pushed the move-elimination/move-elimination branch from 94cd9f4 to 8cc3bd4 Compare October 13, 2026 19:42

JonathanBrouwer mentioned this pull request Oct 20, 2026

Rollup of 15 pull requests #164639

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rust-bors Bot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Oct 20, 2026

Also reject scalable vectors and DynMetadata projections

a1af1ad

rust-bors Bot 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-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Oct 20, 2026

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Rollup of 4 pull requests #164668

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Rollup of 5 pull requests #164673

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rust-bors Bot merged commit 1e956a6 into rust-lang:main Oct 21, 2026
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Toolchain upgrade to nightly-2026-10-22 flux-rs/flux#1847

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