Allow partially moved values in match #103208

cjgillot · 2022-10-18T18:07:12Z

This PR attempts to unify the behaviour between let _ = PLACE, let _: TY = PLACE; and match PLACE { _ => {} }.
The logical conclusion is that the match version should not check for uninitialised places nor check that borrows are still live.

The match PLACE {} case is handled by keeping a FakeRead in the unreachable fallback case to verify that PLACE has a legal value.

Schematically, match PLACE { arms } in surface rust becomes in MIR:

PlaceMention(PLACE)
match PLACE {
  // Decision tree for the explicit arms
  arms,
  // An extra fallback arm
  _ => {
    FakeRead(ForMatchedPlace, PLACE);
    unreachable
  }
}

match *borrow { _ => {} } continues to check that *borrow is live, but does not read the value.
match *borrow {} both checks that *borrow is live, and fake-reads the value.

Continuation of ~~#102256~~ ~~#104844~~

Fixes #99180 #53114

rustbot · 2022-10-18T18:07:15Z

This PR changes MIR

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

rust-highfive · 2022-10-18T18:07:15Z

r? @eholk

(rust-highfive has picked a reviewer for you, use r? to override)

rustbot · 2022-10-18T19:57:04Z

Some changes occurred to the CTFE / Miri engine

cc @rust-lang/miri

Some changes occurred in src/tools/clippy

cc @rust-lang/clippy

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

Some changes occurred in compiler/rustc_codegen_cranelift

cc @bjorn3

compiler/rustc_const_eval/src/interpret/step.rs

pnkfelix · 2022-10-25T18:26:48Z

The lang team wants to have a design meeting about PR #102256 and PR #103208 ; @cjgillot I propose that you and I work together to make a design doc about these changes in terms of what is surfaced at the language level.

scottmcm · 2022-10-25T20:59:44Z

On the let _: Ty = b; example:

What happens there when it's more than just an ascription because it's a coercion site?

For example,

let b: Box<String> = …;
let _: Box<dyn Display> = b;
return b;

I guess that the coercion becomes an explicit statement in MIR, so that would still be rejected even though the AscribeUserType in MIR wouldn't be considered a use any more?

eholk · 2022-10-25T21:27:10Z

I'm probably not the best person to review this, so I'll re-roll.

r? @rust-lang/compiler

bors · 2022-10-31T07:16:44Z

☔ The latest upstream changes (presumably #103787) made this pull request unmergeable. Please resolve the merge conflicts.

lcnr · 2022-10-31T08:49:45Z

r? @oli-obk maybe 🤔 cc @RalfJung

bors · 2022-11-17T05:01:25Z

☔ The latest upstream changes (presumably #103138) made this pull request unmergeable. Please resolve the merge conflicts.

oli-obk · 2022-11-29T15:33:36Z

Triage: This is still waiting on #102256

rustbot · 2023-01-01T13:26:37Z

The Miri subtree was changed

cc @rust-lang/miri

rfcbot · 2023-10-26T20:48:18Z

The final comment period, with a disposition to merge, as per the review above, is now complete.

As the automated representative of the governance process, I would like to thank the author for their work and everyone else who contributed.

This will be merged soon.

RalfJung · 2023-10-27T16:24:15Z

The Miri tests LGTM. @oli-obk wrote

The impl lgtm.

but that was in May. Oli if you could briefly skim this again to make sure it still looks good to you that would be great. :)

oli-obk · 2023-10-27T18:11:42Z

Did another review of the impl and mir opt test changes. Nothing in mir or mir building has changed that would affect these changes, and they look good to me (I don't remember them from the last review, so this was a review from scratch 😅)

@bors r=oli-obk,RalfJung

bors · 2023-10-27T18:11:44Z

📌 Commit 479fb4b has been approved by oli-obk,RalfJung

It is now in the queue for this repository.

bors · 2023-10-27T18:51:46Z

⌛ Testing commit 479fb4b with merge 59bb950...

bors · 2023-10-27T21:10:45Z

☀️ Test successful - checks-actions
Approved by: oli-obk,RalfJung
Pushing 59bb950 to master...

rust-timer · 2023-10-28T00:20:00Z

Finished benchmarking commit (59bb950): comparison URL.

Overall result: no relevant changes - no action needed

@rustbot label: -perf-regression

Instruction count

This benchmark run did not return any relevant results for this metric.

Max RSS (memory usage)

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	1.9%	[1.2%, 3.5%]	4
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Cycles

This benchmark run did not return any relevant results for this metric.

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 635.347s -> 636.148s (0.13%)
Artifact size: 304.54 MiB -> 304.51 MiB (-0.01%)

RalfJung · 2023-10-30T07:37:15Z

It took more than a year, but it's finally done. :) Thanks a lot @cjgillot for seeing this through to the end!

WaffleLapkin · 2023-11-14T00:17:09Z

Should we add relnotes Marks issues that should be documented in the release notes of the next release. here? Might be useful to include in the release notes that we now accept more code

RalfJung · 2023-11-14T06:29:33Z

Sure, why not.

Pkgsrc changes: * Adjust patches and cargo checksums to new versions. * For an external LLVM, set dependency of llvm >= 16, in accordance with the upstream changes. * Mark that on NetBSD we now need >= 9.0, so 8.x is no longer supported. * On NetBSD/sparc64 10.x, we now need GCC 12 to build the embedded LLVM, which is version 17; apparently GCC 10.4 or 10.5 mis-compiles it, resulting in an illegal instruction fault during the build. Ref. rust-lang/rust#117231 Upstream changes: Version 1.75.0 (2023-12-28) ========================== - [Stabilize `async fn` and return-position `impl Trait` in traits.] (rust-lang/rust#115822) - [Allow function pointer signatures containing `&mut T` in `const` contexts.] (rust-lang/rust#116015) - [Match `usize`/`isize` exhaustively with half-open ranges.] (rust-lang/rust#116692) - [Guarantee that `char` has the same size and alignment as `u32`.] (rust-lang/rust#116894) - [Document that the null pointer has the 0 address.] (rust-lang/rust#116988) - [Allow partially moved values in `match`.] (rust-lang/rust#103208) - [Add notes about non-compliant FP behavior on 32bit x86 targets.] (rust-lang/rust#113053) - [Stabilize ratified RISC-V target features.] (rust-lang/rust#116485) Compiler -------- - [Rework negative coherence to properly consider impls that only partly overlap.] (rust-lang/rust#112875) - [Bump `COINDUCTIVE_OVERLAP_IN_COHERENCE` to deny, and warn in dependencies.] (rust-lang/rust#116493) - [Consider alias bounds when computing liveness in NLL.] (rust-lang/rust#116733) - [Add the V (vector) extension to the `riscv64-linux-android` target spec.] (rust-lang/rust#116618) - [Automatically enable cross-crate inlining for small functions] (rust-lang/rust#116505) - Add several new tier 3 targets: - [`csky-unknown-linux-gnuabiv2hf`] (rust-lang/rust#117049) - [`i586-unknown-netbsd`] (rust-lang/rust#117170) - [`mipsel-unknown-netbsd`] (rust-lang/rust#117356) Refer to Rust's [platform support page][platform-support-doc] for more information on Rust's tiered platform support. Libraries --------- - [Override `Waker::clone_from` to avoid cloning `Waker`s unnecessarily.] (rust-lang/rust#96979) - [Implement `BufRead` for `VecDeque<u8>`.] (rust-lang/rust#110604) - [Implement `FusedIterator` for `DecodeUtf16` when the inner iterator does.] (rust-lang/rust#110729) - [Implement `Not, Bit{And,Or}{,Assign}` for IP addresses.] (rust-lang/rust#113747) - [Implement `Default` for `ExitCode`.] (rust-lang/rust#114589) - [Guarantee representation of None in NPO] (rust-lang/rust#115333) - [Document when atomic loads are guaranteed read-only.] (rust-lang/rust#115577) - [Broaden the consequences of recursive TLS initialization.] (rust-lang/rust#116172) - [Windows: Support sub-millisecond sleep.] (rust-lang/rust#116461) - [Fix generic bound of `str::SplitInclusive`'s `DoubleEndedIterator` impl] (rust-lang/rust#100806) - [Fix exit status / wait status on non-Unix `cfg(unix)` platforms.] (rust-lang/rust#115108) Stabilized APIs --------------- - [`Atomic*::from_ptr`] (https://doc.rust-lang.org/stable/core/sync/atomic/struct.AtomicUsize.html#method.from_ptr) - [`FileTimes`] (https://doc.rust-lang.org/stable/std/fs/struct.FileTimes.html) - [`FileTimesExt`] (https://doc.rust-lang.org/stable/std/os/windows/fs/trait.FileTimesExt.html) - [`File::set_modified`] (https://doc.rust-lang.org/stable/std/fs/struct.File.html#method.set_modified) - [`File::set_times`] (https://doc.rust-lang.org/stable/std/fs/struct.File.html#method.set_times) - [`IpAddr::to_canonical`] (https://doc.rust-lang.org/stable/core/net/enum.IpAddr.html#method.to_canonical) - [`Ipv6Addr::to_canonical`] (https://doc.rust-lang.org/stable/core/net/struct.Ipv6Addr.html#method.to_canonical) - [`Option::as_slice`] (https://doc.rust-lang.org/stable/core/option/enum.Option.html#method.as_slice) - [`Option::as_mut_slice`] (https://doc.rust-lang.org/stable/core/option/enum.Option.html#method.as_mut_slice) - [`pointer::byte_add`] (https://doc.rust-lang.org/stable/core/primitive.pointer.html#method.byte_add) - [`pointer::byte_offset`] (https://doc.rust-lang.org/stable/core/primitive.pointer.html#method.byte_offset) - [`pointer::byte_offset_from`] (https://doc.rust-lang.org/stable/core/primitive.pointer.html#method.byte_offset_from) - [`pointer::byte_sub`] (https://doc.rust-lang.org/stable/core/primitive.pointer.html#method.byte_sub) - [`pointer::wrapping_byte_add`] (https://doc.rust-lang.org/stable/core/primitive.pointer.html#method.wrapping_byte_add) - [`pointer::wrapping_byte_offset`] (https://doc.rust-lang.org/stable/core/primitive.pointer.html#method.wrapping_byte_offset) - [`pointer::wrapping_byte_sub`] (https://doc.rust-lang.org/stable/core/primitive.pointer.html#method.wrapping_byte_sub) These APIs are now stable in const contexts: - [`Ipv6Addr::to_ipv4_mapped`] (https://doc.rust-lang.org/stable/core/net/struct.Ipv6Addr.html#method.to_ipv4_mapped) - [`MaybeUninit::assume_init_read`] (https://doc.rust-lang.org/stable/core/mem/union.MaybeUninit.html#method.assume_init_read) - [`MaybeUninit::zeroed`] (https://doc.rust-lang.org/stable/core/mem/union.MaybeUninit.html#method.zeroed) - [`mem::discriminant`] (https://doc.rust-lang.org/stable/core/mem/fn.discriminant.html) - [`mem::zeroed`] (https://doc.rust-lang.org/stable/core/mem/fn.zeroed.html) Cargo ----- - [Add new packages to `[workspace.members]` automatically.] (rust-lang/cargo#12779) - [Allow version-less `Cargo.toml` manifests.] (rust-lang/cargo#12786) - [Make browser links out of HTML file paths.] (rust-lang/cargo#12889) Rustdoc ------- - [Accept less invalid Rust in rustdoc.] (rust-lang/rust#117450) - [Document lack of object safety on affected traits.] (rust-lang/rust#113241) - [Hide `#[repr(transparent)]` if it isn't part of the public ABI.] (rust-lang/rust#115439) - [Show enum discriminant if it is a C-like variant.] (rust-lang/rust#116142) Compatibility Notes ------------------- - [FreeBSD targets now require at least version 12.] (rust-lang/rust#114521) - [Formally demote tier 2 MIPS targets to tier 3.] (rust-lang/rust#115238) - [Make misalignment a hard error in `const` contexts.] (rust-lang/rust#115524) - [Fix detecting references to packed unsized fields.] (rust-lang/rust#115583) - [Remove support for compiler plugins.] (rust-lang/rust#116412)

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cjgillot force-pushed the match-fake-read branch from 26bd3da to 1573932 Compare October 18, 2022 19:57

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pnkfelix mentioned this pull request Oct 25, 2022

Introduce a no-op PlaceMention statement for let _ =. #102256

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cjgillot force-pushed the match-fake-read branch from 3872a79 to 1156aff Compare November 9, 2022 19:44

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[perf] Enable some more MIR optimizations #111061

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Perform opportunistic simplifications during value numbering #111344

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Implement constant propagation on top of MIR SSA analysis #116012

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RalfJung mentioned this pull request Oct 30, 2023

"_" patterns and validity invariants rust-lang/unsafe-code-guidelines#261

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Automated pull from upstream master ferrocene/ferrocene#74

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[nll] _ patterns should not count as borrows #53114

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Stabilize THIR unsafeck #117673

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Allow partially moved values in match #103208

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Allow partially moved values in match #103208

Allow partially moved values in match #103208

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Overall result: no relevant changes - no action needed

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