MIR move elimination [3/6]: PreciseLiveness by Amanieu · Pull Request #163337 · rust-lang/rust

Amanieu · 2026-09-25T15:42:20Z

Depends on #163335

This PR implements the lifetime analysis used by the MoveElimination pass from rust-lang/rfcs#3943.

PreciseLiveness calculates, at a sub-statement granularity, the points in a function where a local requires storage to be allocated. This is more fine-grained than MaybeStorageLive, and takes borrows into account.

r? tmiasko

Amanieu · 2026-09-25T16:04:46Z

LLM disclosure: LLMs were used to double-check the correctness of the analysis against the RFC, Miri and existing MIR passes. It was useful since it found several issues, notably around the behavior of call destination places in the unwind path.

tmiasko · 2026-10-01T07:33:29Z

Would it be possible to test this independently from move elimination?

Amanieu · 2026-10-01T12:44:38Z

We don't really have good infrastructure for testing analysis passes directly. The best I can do is generate some analysis snapshots, but it won't have any CHECK comments since those only look at the final MIR.

My preference is to instead have this tested indirectly through the tests in MoveElimination.

tmiasko · 2026-10-02T08:54:00Z

Perhaps we could annotate final MIR with dataflow results and run file check on it? For example, along the lines of https://github.com/tmiasko/rust/tree/pretty-dataflow.

Amanieu · 2026-10-02T16:47:23Z

Yes, this seems to work, see my latest commit that builds on top of yours. How do you plan to land this? Will you be making a separate PR with your pretty infrastructure?

tmiasko · 2026-10-03T21:33:54Z

Opened #163721 with dataflow pretty printing.

Amanieu · 2026-10-04T20:58:17Z

By the way, I'm not super happy about the name PreciseLiveness and I'm open to ideas about better names.

rustbot · 2026-10-05T20:00:32Z

Some changes occurred in compiler/rustc_attr_parsing

cc @jdonszelmann, @JonathanBrouwer

Some changes occurred in compiler/rustc_attr_ir

cc @jdonszelmann, @JonathanBrouwer

tmiasko · 2026-10-08T17:50:46Z

Thanks. r=me with "Add additional comments & clarify existing ones" and "Address review feedback" incorporated into earlier commits.

Amanieu · 2026-10-08T23:17:38Z

@bors r=tmiasko

rust-bors · 2026-10-08T23:17:41Z

📌 Commit c645363 has been tentatively approved by tmiasko

It will be put into the queue for this repository once PR CI succeeds.

…iveness, r=tmiasko MIR move elimination [3/6]: PreciseLiveness Depends on rust-lang#163335 This PR implements the lifetime analysis used by the `MoveElimination` pass from rust-lang/rfcs#3943. `PreciseLiveness` calculates, at a sub-statement granularity, the points in a function where a local requires storage to be allocated. This is more fine-grained than `MaybeStorageLive`, and takes borrows into account. r? tmiasko

…uwer Rollup of 7 pull requests Successful merges: - #162652 (Syntactically reject leading parenthesized precise capturing lists in bare trait object types (`(use<…>)+`)) - #163337 (MIR move elimination [3/6]: PreciseLiveness) - #163954 (fix(bootstrap/darwin): fix rpath for distributed LLD) - #163956 (Pass the unremapped path to the `rustc` invocation for doctests) - #163634 (move overflow lint computation into decorator) - #163727 (rigid aliases to non-rigid for fully normalized check) - #163745 (replace `fully_monomorphized` with `cx.typing_env()`)

…iveness, r=tmiasko MIR move elimination [3/6]: PreciseLiveness Depends on rust-lang#163335 This PR implements the lifetime analysis used by the `MoveElimination` pass from rust-lang/rfcs#3943. `PreciseLiveness` calculates, at a sub-statement granularity, the points in a function where a local requires storage to be allocated. This is more fine-grained than `MaybeStorageLive`, and takes borrows into account. r? tmiasko

…uwer Rollup of 11 pull requests Successful merges: - #162652 (Syntactically reject leading parenthesized precise capturing lists in bare trait object types (`(use<…>)+`)) - #163337 (MIR move elimination [3/6]: PreciseLiveness) - #163954 (fix(bootstrap/darwin): fix rpath for distributed LLD) - #163956 (Pass the unremapped path to the `rustc` invocation for doctests) - #163634 (move overflow lint computation into decorator) - #163666 (Updates the expect message library/core/src/time.rs) - #163727 (rigid aliases to non-rigid for fully normalized check) - #163745 (replace `fully_monomorphized` with `cx.typing_env()`) - #164000 (When mentioning that closure doesn't implement trait, point at closure) - #164007 ([rustdoc] Prefer local paths over remote ones when foreign item is locally reexported) - #164017 (cg_llvm: Avoid some explicit casts to `*const c_char`)

…iveness, r=tmiasko MIR move elimination [3/6]: PreciseLiveness Depends on rust-lang#163335 This PR implements the lifetime analysis used by the `MoveElimination` pass from rust-lang/rfcs#3943. `PreciseLiveness` calculates, at a sub-statement granularity, the points in a function where a local requires storage to be allocated. This is more fine-grained than `MaybeStorageLive`, and takes borrows into account. r? tmiasko

…uwer Rollup of 14 pull requests Successful merges: - #162652 (Syntactically reject leading parenthesized precise capturing lists in bare trait object types (`(use<…>)+`)) - #163337 (MIR move elimination [3/6]: PreciseLiveness) - #163954 (fix(bootstrap/darwin): fix rpath for distributed LLD) - #163193 (cfi: mangle `f128` as `e` rather than `g` on platforms without `_Float128`) - #163634 (move overflow lint computation into decorator) - #163666 (Updates the expect message library/core/src/time.rs) - #163727 (rigid aliases to non-rigid for fully normalized check) - #163745 (replace `fully_monomorphized` with `cx.typing_env()`) - #163912 (Fix debug assert failure in `note_obligation_cause_code_inner`) - #163972 (const-eval: ICE when we hit a non-const fn) - #164000 (When mentioning that closure doesn't implement trait, point at closure) - #164007 ([rustdoc] Prefer local paths over remote ones when foreign item is locally reexported) - #164017 (cg_llvm: Avoid some explicit casts to `*const c_char`) - #164025 (Less `CanonicalVarValues`)

…iveness, r=tmiasko MIR move elimination [3/6]: PreciseLiveness Depends on rust-lang#163335 This PR implements the lifetime analysis used by the `MoveElimination` pass from rust-lang/rfcs#3943. `PreciseLiveness` calculates, at a sub-statement granularity, the points in a function where a local requires storage to be allocated. This is more fine-grained than `MaybeStorageLive`, and takes borrows into account. r? tmiasko

…uwer Rollup of 14 pull requests Successful merges: - #162652 (Syntactically reject leading parenthesized precise capturing lists in bare trait object types (`(use<…>)+`)) - #163337 (MIR move elimination [3/6]: PreciseLiveness) - #163954 (fix(bootstrap/darwin): fix rpath for distributed LLD) - #163193 (cfi: mangle `f128` as `e` rather than `g` on platforms without `_Float128`) - #163634 (move overflow lint computation into decorator) - #163666 (Updates the expect message library/core/src/time.rs) - #163727 (rigid aliases to non-rigid for fully normalized check) - #163745 (replace `fully_monomorphized` with `cx.typing_env()`) - #163912 (Fix debug assert failure in `note_obligation_cause_code_inner`) - #163950 (don't treat inherited opaques as defining) - #164000 (When mentioning that closure doesn't implement trait, point at closure) - #164007 ([rustdoc] Prefer local paths over remote ones when foreign item is locally reexported) - #164017 (cg_llvm: Avoid some explicit casts to `*const c_char`) - #164025 (Less `CanonicalVarValues`)

…uwer Rollup of 24 pull requests Successful merges: - #161998 ( Support type-relative assoc item paths in generic param defaults & const param types) - #162106 (Helpful suggestions for incorrect address-of mutability (2)) - #162652 (Syntactically reject leading parenthesized precise capturing lists in bare trait object types (`(use<…>)+`)) - #163337 (MIR move elimination [3/6]: PreciseLiveness) - #163938 (-Zassumptions-on-binders: rewrite alias outlives constraints more goodly) - #163939 (Better debug impls for some assumptions on binders types) - #163954 (fix(bootstrap/darwin): fix rpath for distributed LLD) - #163956 (Pass the unremapped path to the `rustc` invocation for doctests) - #164042 (Allow testing cg-gcc on any target) - #162443 (Do not retain `Normalization` goal errors in nested goals for `BestObligationVisitor:: non_trivial_candidates `) - #162908 (Fix - const parameters rejected when identical) - #163193 (cfi: mangle `f128` as `e` rather than `g` on platforms without `_Float128`) - #163634 (move overflow lint computation into decorator) - #163666 (Updates the expect message library/core/src/time.rs) - #163727 (rigid aliases to non-rigid for fully normalized check) - #163745 (replace `fully_monomorphized` with `cx.typing_env()`) - #163912 (Fix debug assert failure in `note_obligation_cause_code_inner`) - #163950 (don't treat inherited opaques as defining) - #163972 (const-eval: ICE when we hit a non-const fn) - #164000 (When mentioning that closure doesn't implement trait, point at closure) - #164007 ([rustdoc] Prefer local paths over remote ones when foreign item is locally reexported) - #164008 (properly ignore the current goal's usages) - #164017 (cg_llvm: Avoid some explicit casts to `*const c_char`) - #164025 (Less `CanonicalVarValues`)

Rollup merge of #163337 - Amanieu:move-elimination/precise-liveness, r=tmiasko MIR move elimination [3/6]: PreciseLiveness Depends on #163335 This PR implements the lifetime analysis used by the `MoveElimination` pass from rust-lang/rfcs#3943. `PreciseLiveness` calculates, at a sub-statement granularity, the points in a function where a local requires storage to be allocated. This is more fine-grained than `MaybeStorageLive`, and takes borrows into account. r? tmiasko

rustbot assigned tmiasko Sep 25, 2026

Amanieu added the llm-assisted An LLM-assisted PR as defined by the LLM policy. Requires ahead-of-time consent by assignee. label Sep 25, 2026

Amanieu mentioned this pull request Sep 25, 2026

Implement RFC 3943: MIR move elimination #157943

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Amanieu force-pushed the move-elimination/precise-liveness branch from e7ac990 to 191a6f0 Compare September 26, 2026 01:05

This was referenced Sep 26, 2026

MIR move elimination [4/6]: MoveElimination #163338

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MIR move elimination rust-lang/goals#396

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tmiasko mentioned this pull request Sep 30, 2026

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

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Amanieu force-pushed the move-elimination/precise-liveness branch from 191a6f0 to 8f7b938 Compare September 30, 2026 12:49

Amanieu marked this pull request as ready for review September 30, 2026 13:03

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Sep 30, 2026

Amanieu force-pushed the move-elimination/precise-liveness branch from 8f7b938 to 1c34f63 Compare September 30, 2026 13:03

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Amanieu mentioned this pull request Oct 1, 2026

Add merge yields pass #162429

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Re-introduce ResultsVisitor::visit_block_exit

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Amanieu force-pushed the move-elimination/precise-liveness branch from b1a44c7 to 3f7db5c Compare October 5, 2026 20:00

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tmiasko reviewed Oct 6, 2026

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Comment thread tests/mir-opt/precise_liveness.rs

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Comment thread compiler/rustc_mir_dataflow/src/impls/precise_liveness.rs

Amanieu added 2 commits October 9, 2026 00:10

Add precise MIR liveness analysis

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Add dataflow tests for PreciseLiveness

c645363

Amanieu force-pushed the move-elimination/precise-liveness branch from 02741ef to c645363 Compare October 8, 2026 23:13

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-review Status: Awaiting review from the assignee but also interested parties. labels Oct 8, 2026

JonathanBrouwer mentioned this pull request Oct 9, 2026

Rollup of 7 pull requests #164015

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JonathanBrouwer mentioned this pull request Oct 9, 2026

Rollup of 11 pull requests #164024

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Rollup of 14 pull requests #164026

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Rollup of 14 pull requests #164027

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Rollup of 14 pull requests #164039

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Rollup of 24 pull requests #164052

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rust-bors Bot merged commit 98476db into rust-lang:main Oct 9, 2026
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rustbot added this to the 1.101.0 milestone Oct 9, 2026

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