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Optimize away poison guards when std is built with panic=abort #100603
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Hey! It looks like you've submitted a new PR for the library teams! If this PR contains changes to any Examples of
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r? @thomcc (rust-highfive has picked a reviewer for you, use r? to override) |
@rustbot label +T-libs-api -T-libs |
I'm in favor of this, but am unsure if it constitutes a breaking change. Either way, I think this probably needs an FCP. I'm going to reassign to someone on t-libs-api for that. r? @m-ou-se |
@rustbot label +I-libs-api-nominated |
Why not leave PoisonError the way it was, with an always working |
The reason for the change to PoisonError is to make code paths that check the result of locking a Mutex trivially optimize away. I'd like the lock code we generate to be the same as if you hand-rolled an implementation without poisoning. In theory this can be done with enough inlining and optimizations turned on, without a change to PoisonError. I can investigate that. It probably requires playing with |
@@ -267,6 +313,7 @@ where | |||
{ | |||
match result { | |||
Ok(t) => Ok(f(t)), | |||
#[cfg(panic = "unwind")] |
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map_result
isn't public API so instead of removing the variant you could add an unreachable_unchecked
in this
@tmandry any updates on this? thanks |
@rust-lang/libs-api: I am in favor of this, including the change to make |
Team member @dtolnay has proposed to merge this. The next step is review by the rest of the tagged team members: No concerns currently listed. Once a majority of reviewers approve (and at most 2 approvals are outstanding), this will enter its final comment period. If you spot a major issue that hasn't been raised at any point in this process, please speak up! See this document for info about what commands tagged team members can give me. |
I was actually looking into something similar, but where However it would be a (slight) breaking change since |
🔔 This is now entering its final comment period, as per the review above. 🔔 |
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. |
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Thank you!
@bors r+ |
@bors ping |
@bors ping |
😪 I'm awake I'm awake |
@bors r+ |
☀️ Test successful - checks-actions |
Finished benchmarking commit (81b757c): comparison URL. Overall result: no relevant changes - no action needed@rustbot label: -perf-regression Instruction countThis benchmark run did not return any relevant results for this metric. Max RSS (memory usage)This benchmark run did not return any relevant results for this metric. CyclesThis benchmark run did not return any relevant results for this metric. Binary sizeThis benchmark run did not return any relevant results for this metric. Bootstrap: 632.818s -> 633.405s (0.09%) |
Upgrade toolchain to 2024-02-17. Relevant PR: - rust-lang/rust#120500 - rust-lang/rust#100603 Fixes #87 Fixes #3034 Fixes #3037
Pkgsrc changes: * Adapt checksums and patches, some have beene intregrated upstream. Upstream chnages: Version 1.78.0 (2024-05-02) =========================== Language -------- - [Stabilize `#[cfg(target_abi = ...)]`] (rust-lang/rust#119590) - [Stabilize the `#[diagnostic]` namespace and `#[diagnostic::on_unimplemented]` attribute] (rust-lang/rust#119888) - [Make async-fn-in-trait implementable with concrete signatures] (rust-lang/rust#120103) - [Make matching on NaN a hard error, and remove the rest of `illegal_floating_point_literal_pattern`] (rust-lang/rust#116284) - [static mut: allow mutable reference to arbitrary types, not just slices and arrays] (rust-lang/rust#117614) - [Extend `invalid_reference_casting` to include references casting to bigger memory layout] (rust-lang/rust#118983) - [Add `non_contiguous_range_endpoints` lint for singleton gaps after exclusive ranges] (rust-lang/rust#118879) - [Add `wasm_c_abi` lint for use of older wasm-bindgen versions] (rust-lang/rust#117918) This lint currently only works when using Cargo. - [Update `indirect_structural_match` and `pointer_structural_match` lints to match RFC] (rust-lang/rust#120423) - [Make non-`PartialEq`-typed consts as patterns a hard error] (rust-lang/rust#120805) - [Split `refining_impl_trait` lint into `_reachable`, `_internal` variants] (rust-lang/rust#121720) - [Remove unnecessary type inference when using associated types inside of higher ranked `where`-bounds] (rust-lang/rust#119849) - [Weaken eager detection of cyclic types during type inference] (rust-lang/rust#119989) - [`trait Trait: Auto {}`: allow upcasting from `dyn Trait` to `dyn Auto`] (rust-lang/rust#119338) Compiler -------- - [Made `INVALID_DOC_ATTRIBUTES` lint deny by default] (rust-lang/rust#111505) - [Increase accuracy of redundant `use` checking] (rust-lang/rust#117772) - [Suggest moving definition if non-found macro_rules! is defined later] (rust-lang/rust#121130) - [Lower transmutes from int to pointer type as gep on null] (rust-lang/rust#121282) Target changes: - [Windows tier 1 targets now require at least Windows 10] (rust-lang/rust#115141) - [Enable CMPXCHG16B, SSE3, SAHF/LAHF and 128-bit Atomics in tier 1 Windows] (rust-lang/rust#120820) - [Add `wasm32-wasip1` tier 2 (without host tools) target] (rust-lang/rust#120468) - [Add `wasm32-wasip2` tier 3 target] (rust-lang/rust#119616) - [Rename `wasm32-wasi-preview1-threads` to `wasm32-wasip1-threads`] (rust-lang/rust#122170) - [Add `arm64ec-pc-windows-msvc` tier 3 target] (rust-lang/rust#119199) - [Add `armv8r-none-eabihf` tier 3 target for the Cortex-R52] (rust-lang/rust#110482) - [Add `loongarch64-unknown-linux-musl` tier 3 target] (rust-lang/rust#121832) Refer to Rust's [platform support page][platform-support-doc] for more information on Rust's tiered platform support. Libraries --------- - [Bump Unicode to version 15.1.0, regenerate tables] (rust-lang/rust#120777) - [Make align_offset, align_to well-behaved in all cases] (rust-lang/rust#121201) - [PartialEq, PartialOrd: document expectations for transitive chains] (rust-lang/rust#115386) - [Optimize away poison guards when std is built with panic=abort] (rust-lang/rust#100603) - [Replace pthread `RwLock` with custom implementation] (rust-lang/rust#110211) - [Implement unwind safety for Condvar on all platforms] (rust-lang/rust#121768) - [Add ASCII fast-path for `char::is_grapheme_extended`] (rust-lang/rust#121138) Stabilized APIs --------------- - [`impl Read for &Stdin`] (https://doc.rust-lang.org/stable/std/io/struct.Stdin.html#impl-Read-for-%26Stdin) - [Accept non `'static` lifetimes for several `std::error::Error` related implementations] (rust-lang/rust#113833) - [Make `impl<Fd: AsFd>` impl take `?Sized`] (rust-lang/rust#114655) - [`impl From<TryReserveError> for io::Error`] (https://doc.rust-lang.org/stable/std/io/struct.Error.html#impl-From%3CTryReserveError%3E-for-Error) These APIs are now stable in const contexts: - [`Barrier::new()`] (https://doc.rust-lang.org/stable/std/sync/struct.Barrier.html#method.new) Cargo ----- - [Stabilize lockfile v4](rust-lang/cargo#12852) - [Respect `rust-version` when generating lockfile] (rust-lang/cargo#12861) - [Control `--charset` via auto-detecting config value] (rust-lang/cargo#13337) - [Support `target.<triple>.rustdocflags` officially] (rust-lang/cargo#13197) - [Stabilize global cache data tracking] (rust-lang/cargo#13492) Misc ---- - [rustdoc: add `--test-builder-wrapper` arg to support wrappers such as RUSTC_WRAPPER when building doctests] (rust-lang/rust#114651) Compatibility Notes ------------------- - [Many unsafe precondition checks now run for user code with debug assertions enabled] (rust-lang/rust#120594) This change helps users catch undefined behavior in their code, though the details of how much is checked are generally not stable. - [riscv only supports split_debuginfo=off for now] (rust-lang/rust#120518) - [Consistently check bounds on hidden types of `impl Trait`] (rust-lang/rust#121679) - [Change equality of higher ranked types to not rely on subtyping] (rust-lang/rust#118247) - [When called, additionally check bounds on normalized function return type] (rust-lang/rust#118882) - [Expand coverage for `arithmetic_overflow` lint] (rust-lang/rust#119432) Internal Changes ---------------- These changes do not affect any public interfaces of Rust, but they represent significant improvements to the performance or internals of rustc and related tools. - [Update to LLVM 18](rust-lang/rust#120055) - [Build `rustc` with 1CGU on `x86_64-pc-windows-msvc`] (rust-lang/rust#112267) - [Build `rustc` with 1CGU on `x86_64-apple-darwin`] (rust-lang/rust#112268) - [Introduce `run-make` V2 infrastructure, a `run_make_support` library and port over 2 tests as example] (rust-lang/rust#113026) - [Windows: Implement condvar, mutex and rwlock using futex] (rust-lang/rust#121956)
When std is compiled with
panic=abort
we can remove a lot of the poison machinery from the locks. This changes theFlag
andGuard
types to be ZSTs. It also adds an uninhabited member toPoisonError
so the compiler knows it can optimize away theResult::Err
paths, and makeLockResult<T>
layout-equivalent toT
.Is this a breaking change?
PoisonError::new
now panics if invoked from a libstd built withpanic="abort"
(or any non-unwind
strategy). It is unclear to me whether to consider this a breaking change.In order to encounter this behavior, both of the following must be true:
Using a libstd with
panic="abort"
This is pretty uncommon. We don't build libstd with that in rustup, except in (Tier 2-3) platforms that do not support unwinding, most notably wasm.
Most people who do this are using cargo's
-Z build-std
feature, which is unstable.panic="abort"
is not a supported option in Rust's build system. It is possible to configure it usingCARGO_TARGET_xxx_RUSTFLAGS
, but I believe this only works on non-host platforms.Creating
PoisonError
manuallyThis is also unlikely. The only common use case I can think of is in tests, and you can't run tests with
panic="abort"
without the unstable-Z panic_abort_tests
flag.It's possible that someone is implementing their own locks using std's
PoisonError
and defining "thread failure" to mean something other than "panic". If this is the case then we would break their code if it was used with apanic="abort"
libstd. The locking crates I know of don't replicate std's poison API, but I haven't done much research into this yet.I've touched on a fair number of considerations here. Which ones do people consider relevant?