Improve performance of coherence checks #68966
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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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Queued fe57f83 with parent 85ffd44, future comparison URL. |
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r=me if perf looks good. |
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5-8% improvement in @bors r=varkor |
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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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…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: 
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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
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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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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: