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Improve performance of coherence checks #68966

Merged
merged 4 commits into from
Feb 10, 2020
Merged

Improve performance of coherence checks #68966

merged 4 commits into from
Feb 10, 2020

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jonas-schievink
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@jonas-schievink jonas-schievink commented Feb 8, 2020

The biggest perf improvement in here is expected to come from the removal of the remaining #43355 warning code since that effectively runs the expensive parts of coherence twice, which can even be visualized by obtaining a flamegraph:

image

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r? @varkor

(rust_highfive has picked a reviewer for you, use r? to override)

@rust-highfive rust-highfive added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Feb 8, 2020
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@bors try @rust-timer queue

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Awaiting bors try build completion

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bors commented Feb 8, 2020

⌛ Trying commit 14a15d6 with merge fe57f83...

bors added a commit that referenced this pull request Feb 8, 2020
Improve performance of coherence checks

The biggest perf improvement in here is expected to come from the removal of the remaining #43355 warning code since the effectively runs the expensive parts of coherence *twice* (which can even be visualized by obtaining a flamegraph https://twitter.com/sheevink/status/1225963187511709696).
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(Edited description to inline the image link to hopefully have it not get lost to time as easily)

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bors commented Feb 8, 2020

☀️ Try build successful - checks-azure
Build commit: fe57f83 (fe57f83be5309ba42c3dccaa488d1dad3ca6d863)

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Queued fe57f83 with parent 85ffd44, future comparison URL.

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varkor commented Feb 9, 2020

r=me if perf looks good.

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5-8% improvement in packed-simd, no regressions.

@bors r=varkor

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bors commented Feb 9, 2020

📌 Commit 14a15d6 has been approved by varkor

@bors bors 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 Feb 9, 2020
This has negligible perf impact, but it does improve the code a bit.

* Only query the specialization graph of any trait once instead of once per
  impl
* Loop over impls only once, precomputing impl DefId and TraitRef
This was showing up in profiles. Also deduplicates the code to get just
the impl header span.
This was previously a future-compat warning that has since been turned into
hard error, but without actually removing all the code.

Avoids a call to `traits::overlapping_impls`, which is expensive.
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@bors r=varkor

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bors commented Feb 9, 2020

📌 Commit 2309592 has been approved by varkor

Dylan-DPC-zz pushed a commit to Dylan-DPC-zz/rust that referenced this pull request Feb 10, 2020
…arkor

Improve performance of coherence checks

The biggest perf improvement in here is expected to come from the removal of the remaining rust-lang#43355 warning code since that effectively runs the expensive parts of coherence *twice*, which can even be visualized by obtaining a flamegraph:

![image](https://user-images.githubusercontent.com/5047365/74091959-e1f41200-4a8b-11ea-969d-2849d3f86c63.png)
bors added a commit that referenced this pull request Feb 10, 2020
Rollup of 6 pull requests

Successful merges:

 - #68694 (Reduce the number of `RefCell`s in `InferCtxt`.)
 - #68966 (Improve performance of coherence checks)
 - #68976 (Make `num::NonZeroX::new` an unstable `const fn`)
 - #68992 (Correctly parse `mut a @ b`)
 - #69005 (Small graphviz improvements for the new dataflow framework)
 - #69006 (parser: Keep current and previous tokens precisely)

Failed merges:

r? @ghost
@bors bors merged commit 2309592 into rust-lang:master Feb 10, 2020
@jonas-schievink jonas-schievink deleted the coherence-perf branch March 13, 2020 16:06
@jonas-schievink jonas-schievink added relnotes Marks issues that should be documented in the release notes of the next release. relnotes-perf Performance improvements that should be mentioned in the release notes. labels Mar 13, 2020
@jonas-schievink jonas-schievink modified the milestones: 1.44, 1.43 Mar 13, 2020
netbsd-srcmastr pushed a commit to NetBSD/pkgsrc that referenced this pull request May 16, 2020
Pkgsrc changes:
 * Bump rust bootstrap version to 1.42.0, except for Darwin/i686 where the
   bootstrap is not (yet?) available.

Upstream changes:

Version 1.43.0 (2020-04-23)
==========================

Language
--------
- [Fixed using binary operations with `&{number}` (e.g. `&1.0`) not having
  the type inferred correctly.][68129]
- [Attributes such as `#[cfg()]` can now be used on `if` expressions.][69201]

**Syntax only changes**
- [Allow `type Foo: Ord` syntactically.][69361]
- [Fuse associated and extern items up to defaultness.][69194]
- [Syntactically allow `self` in all `fn` contexts.][68764]
- [Merge `fn` syntax + cleanup item parsing.][68728]
- [`item` macro fragments can be interpolated into `trait`s, `impl`s,
  and `extern` blocks.][69366]
  For example, you may now write:
  ```rust
  macro_rules! mac_trait {
      ($i:item) => {
          trait T { $i }
      }
  }
  mac_trait! {
      fn foo() {}
  }
  ```
These are still rejected *semantically*, so you will likely receive an error but
these changes can be seen and parsed by macros and
conditional compilation.


Compiler
--------
- [You can now pass multiple lint flags to rustc to override the previous
  flags.][67885] For example; `rustc -D unused -A unused-variables` denies
  everything in the `unused` lint group except `unused-variables` which
  is explicitly allowed. However, passing `rustc -A unused-variables -D unused` denies
  everything in the `unused` lint group **including** `unused-variables` since
  the allow flag is specified before the deny flag (and therefore overridden).
- [rustc will now prefer your system MinGW libraries over its bundled libraries
  if they are available on `windows-gnu`.][67429]
- [rustc now buffers errors/warnings printed in JSON.][69227]

Libraries
---------
- [`Arc<[T; N]>`, `Box<[T; N]>`, and `Rc<[T; N]>`, now implement
  `TryFrom<Arc<[T]>>`,`TryFrom<Box<[T]>>`, and `TryFrom<Rc<[T]>>`
  respectively.][69538] **Note** These conversions are only available when `N`
  is `0..=32`.
- [You can now use associated constants on floats and integers directly, rather
  than having to import the module.][68952] e.g. You can now write `u32::MAX` or
  `f32::NAN` with no imports.
- [`u8::is_ascii` is now `const`.][68984]
- [`String` now implements `AsMut<str>`.][68742]
- [Added the `primitive` module to `std` and `core`.][67637] This module
  reexports Rust's primitive types. This is mainly useful in macros
  where you want avoid these types being shadowed.
- [Relaxed some of the trait bounds on `HashMap` and `HashSet`.][67642]
- [`string::FromUtf8Error` now implements `Clone + Eq`.][68738]

Stabilized APIs
---------------
- [`Once::is_completed`]
- [`f32::LOG10_2`]
- [`f32::LOG2_10`]
- [`f64::LOG10_2`]
- [`f64::LOG2_10`]
- [`iter::once_with`]

Cargo
-----
- [You can now set config `[profile]`s in your `.cargo/config`, or through
  your environment.][cargo/7823]
- [Cargo will now set `CARGO_BIN_EXE_<name>` pointing to a binary's
  executable path when running integration tests or benchmarks.][cargo/7697]
  `<name>` is the name of your binary as-is e.g. If you wanted the executable
  path for a binary named `my-program`you would use
  `env!("CARGO_BIN_EXE_my-program")`.

Misc
----
- [Certain checks in the `const_err` lint were deemed unrelated to const
  evaluation][69185], and have been moved to the `unconditional_panic` and
  `arithmetic_overflow` lints.

Compatibility Notes
-------------------

- [Having trailing syntax in the `assert!` macro is now a hard error.][69548]
  This has been a warning since 1.36.0.
- [Fixed `Self` not having the correctly inferred type.][69340] This incorrectly
  led to some instances being accepted, and now correctly emits a hard error.

[69340]: rust-lang/rust#69340

Internal Only
-------------
These changes provide no direct user facing benefits, but represent significant
improvements to the internals and overall performance of `rustc` and
related tools.

- [All components are now built with `opt-level=3` instead of `2`.][67878]
- [Improved how rustc generates drop code.][67332]
- [Improved performance from `#[inline]`-ing certain hot functions.][69256]
- [traits: preallocate 2 Vecs of known initial size][69022]
- [Avoid exponential behaviour when relating types][68772]
- [Skip `Drop` terminators for enum variants without drop glue][68943]
- [Improve performance of coherence checks][68966]
- [Deduplicate types in the generator witness][68672]
- [Invert control in struct_lint_level.][68725]

[67332]: rust-lang/rust#67332
[67429]: rust-lang/rust#67429
[67637]: rust-lang/rust#67637
[67642]: rust-lang/rust#67642
[67878]: rust-lang/rust#67878
[67885]: rust-lang/rust#67885
[68129]: rust-lang/rust#68129
[68672]: rust-lang/rust#68672
[68725]: rust-lang/rust#68725
[68728]: rust-lang/rust#68728
[68738]: rust-lang/rust#68738
[68742]: rust-lang/rust#68742
[68764]: rust-lang/rust#68764
[68772]: rust-lang/rust#68772
[68943]: rust-lang/rust#68943
[68952]: rust-lang/rust#68952
[68966]: rust-lang/rust#68966
[68984]: rust-lang/rust#68984
[69022]: rust-lang/rust#69022
[69185]: rust-lang/rust#69185
[69194]: rust-lang/rust#69194
[69201]: rust-lang/rust#69201
[69227]: rust-lang/rust#69227
[69548]: rust-lang/rust#69548
[69256]: rust-lang/rust#69256
[69361]: rust-lang/rust#69361
[69366]: rust-lang/rust#69366
[69538]: rust-lang/rust#69538
[cargo/7823]: rust-lang/cargo#7823
[cargo/7697]: rust-lang/cargo#7697
[`Once::is_completed`]: https://doc.rust-lang.org/std/sync/struct.Once.html#method.is_completed
[`f32::LOG10_2`]: https://doc.rust-lang.org/std/f32/consts/constant.LOG10_2.html
[`f32::LOG2_10`]: https://doc.rust-lang.org/std/f32/consts/constant.LOG2_10.html
[`f64::LOG10_2`]: https://doc.rust-lang.org/std/f64/consts/constant.LOG10_2.html
[`f64::LOG2_10`]: https://doc.rust-lang.org/std/f64/consts/constant.LOG2_10.html
[`iter::once_with`]: https://doc.rust-lang.org/std/iter/fn.once_with.html
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