Scott McMurray [Fri, 4 Sep 2020 02:59:51 +0000 (19:59 -0700)]
Add `[T; N]: TryFrom<Vec<T>>`
This is very similar to the existing `Box<[T; N]>: TryFrom<Box<[T]>>`, but allows avoiding the `shrink_to_fit` if you have a vector and not a boxed slice.
Auto merge of #70793 - the8472:in-place-iter-collect, r=Amanieu
specialize some collection and iterator operations to run in-place
This is a rebase and update of #66383 which was closed due inactivity.
Recent rustc changes made the compile time regressions disappear, at least for webrender-wrench. Running a stage2 compile and the rustc-perf suite takes hours on the hardware I have at the moment, so I can't do much more than that.
In the best case of the `vec::bench_in_place_recycle` synthetic microbenchmark these optimizations can provide a 15x speedup over the regular implementation which allocates a new vec for every benchmark iteration. [Benchmark results](https://gist.github.com/the8472/6d999b2d08a2bedf3b93f12112f96e2f). In real code the speedups are tiny, but it also depends on the allocator used, a system allocator that uses a process-wide mutex will benefit more than one with thread-local pools.
## What was changed
* `SpecExtend` which covered `from_iter` and `extend` specializations was split into separate traits
* `extend` and `from_iter` now reuse the `append_elements` if passed iterators are from slices.
* A preexisting `vec.into_iter().collect::<Vec<_>>()` optimization that passed through the original vec has been generalized further to also cover cases where the original has been partially drained.
* A chain of *Vec<T> / BinaryHeap<T> / Box<[T]>* `IntoIter`s through various iterator adapters collected into *Vec<U>* and *BinaryHeap<U>* will be performed in place as long as `T` and `U` have the same alignment and size and aren't ZSTs.
* To enable above specialization the unsafe, unstable `SourceIter` and `InPlaceIterable` traits have been added. The first allows reaching through the iterator pipeline to grab a pointer to the source memory. The latter is a marker that promises that the read pointer will advance as fast or faster than the write pointer and thus in-place operation is possible in the first place.
* `vec::IntoIter` implements `TrustedRandomAccess` for `T: Copy` to allow in-place collection when there is a `Zip` adapter in the iterator. TRA had to be made an unstable public trait to support this.
`vec.into_iter().filter(|_| false).collect()` will no longer return a vec with 0 capacity, instead it will return its original allocation. This avoids the cost of doing any allocation or deallocation but could lead to large allocations living longer than expected.
If that's not acceptable some resizing policy at the end of the attempted in-place collect would be necessary, which in the worst case could result in one more memcopy than the non-specialized case.
## Possible followup work
* split liballoc/vec.rs to remove `ignore-tidy-filelength`
* try to get trivial chains such as `vec.into_iter().skip(1).collect::<Vec<)>>()` to compile to a `memmove` (currently compiles to a pile of SIMD, see #69187 )
* improve up the traits so they can be reused by other crates, e.g. itertools. I think currently they're only good enough for internal use
* allow iterators sourced from a `HashSet` to be in-place collected into a `Vec`
The InPlaceIterable debug assert checks that the write pointer
did not advance beyond the read pointer. But TrustedRandomAccess
never advances the read pointer, thus triggering the assert.
Skip the assert if the source pointer did not change during iteration.
Unfortunately this is not quite ready to go because the newly-working links trigger a bunch of linkcheck failures. The failures are tough to fix because the links are resolved relative to the implementor, which could be anywhere in the module hierarchy.
(In the current docs, these links end up rendering as uninterpreted markdown syntax, so I don't think these failures are any worse than the status quo. It might be acceptable to just add them to the linkchecker whitelist.)
Ideally this could be fixed with intra-doc links ~~but it isn't working for me: I am currently investigating if it's possible to solve it this way.~~ Opened #73829.
The8472 [Wed, 26 Aug 2020 21:24:34 +0000 (23:24 +0200)]
remove empty Vec extend optimization
The optimization meant that every extend code path had to emit llvm
IR for from_iter and extend spec_extend, which likely impacts
compile times while only improving a few edge-cases
The8472 [Sun, 24 May 2020 01:23:15 +0000 (03:23 +0200)]
avoid applying in-place collect specialization in type-length test
the test was sized to match external iteration only, since
vec's in-place collect now uses internal iteration we collect into
a different type now.
Note that any other try-fold based operation such as count() would also
have exceeded the type length limit for that iterator.
Auto merge of #76235 - jyn514:std-intra-links, r=poliorcetics
Convert many files to intra-doc links
Helps with https://github.com/rust-lang/rust/issues/75080
r? @poliorcetics
I recommend reviewing one commit at a time, but the diff is small enough you can do it all at once if you like :)
Auto merge of #75971 - Amjad50:libstd-deny-unsafe_op_in_unsafe_fn, r=Mark-Simulacrum
Applied `#![deny(unsafe_op_in_unsafe_fn)]` in library/std/src/wasi
partial fix for #73904
There are still more that was not applied in [mod.rs]( https://github.com/rust-lang/rust/blob/38fab2ea92a48980219989817201bf2094ae826a/library/std/src/sys/wasi/mod.rs) and that is due to its using files from `../unsupported`
like:
```
#[path = "../unsupported/cmath.rs"]
pub mod cmath;
```
Rollup merge of #76255 - ehuss:update-books, r=ehuss
Update books
## reference
4 commits in 1b6c4b0afab97c0230433466c97167bbbe8445f6..25391dba46262f882fa846beefaff54a966a8fa5
2020-08-18 17:04:28 -0700 to 2020-09-02 07:22:55 -0700
- clarify when reading uninititalized memory is allowed (rust-lang-nursery/reference#852)
- Update patterns chapter, add rest patterns. (rust-lang-nursery/reference#876)
- Improve Type-Coersion Documentation (rust-lang-nursery/reference#843)
- Added variable back into example. (rust-lang-nursery/reference#880)
## book
3 commits in c0a6a61b8205da14ac955425f74258ffd8ee065d..e5ed97128302d5fa45dbac0e64426bc7649a558c
2020-08-14 14:21:49 -0500 to 2020-08-31 12:53:40 -0500
- Fix type mismatch in listing 10-5 (rust-lang/book#2441)
- Update ppendix-06-translation.md (rust-lang/book#2437)
- Correct no-listing-10-result-in-tests: Take tests module out of the main function (rust-lang/book#2430)
## rust-by-example
3 commits in 80a10e22140e28392b99d24ed02f4c6d8cb770a0..19f0a0372af497b34369cf182d9d16156cab2969
2020-08-08 09:56:46 -0300 to 2020-08-26 09:38:48 -0300
- prefer `length` over `size` when talking about number of elements vs. bytesize (rust-lang/rust-by-example#1372)
- Split out variable shadowing into a separate example (rust-lang/rust-by-example#1370)
- Update extern crate related sections (rust-lang/rust-by-example#1369)
Rollup merge of #76245 - tmiasko:inline-generators, r=ecstatic-morse
inliner: Avoid query cycles when optimizing generators
The HIR Id trick is insufficient to prevent query cycles when optimizing
generators, since merely requesting a layout of a generator also
computes its `optimized_mir`.
Make no attempts to inline functions into generators within the same
crate to avoid query cycles.
Rollup merge of #76243 - ama0:patch-1, r=jonas-schievink
Fix typos in vec try_reserve(_exact) docs
`try_reserve` and `try_reserve_exact` docs refer to calling `reserve` and `reserve_exact`.
`try_reserve_exact` example uses `try_reserve` method instead of `try_reserve_exact`.
Rollup merge of #76242 - RalfJung:read-fixme, r=Dylan-DPC
Read: adjust a FIXME reference
There's already another reference to https://github.com/rust-lang/rust/issues/42788 for basically the same problem, so lets reuse it here:
https://github.com/rust-lang/rust/blob/5e208efaa850efaa97495e81c49cf0f5767e8f49/library/std/src/io/mod.rs#L369-L376
Rollup merge of #76238 - denisvasilik:intra-doc-links-core-iterator, r=jyn514
Move to intra-doc links for library/core/src/iter/traits/iterator.rs
Helps with #75080.
@jyn514 We're almost finished with this issue. Thanks for mentoring. If you have other topics to work on just let me know, I will be around in Discord.
Rollup merge of #76120 - LukasKalbertodt:add-as-slice-method-to-array, r=Mark-Simulacrum
Add `[T; N]::as_[mut_]slice`
Part of me trying to populate arrays with a couple of basic useful methods, like slices already have. The ability to add methods to arrays were added in #75212. Tracking issue: #76118
Rollup merge of #75150 - nanpuyue:deprecate_to_ipv6_compatible, r=LukasKalbertodt
Add a note for Ipv4Addr::to_ipv6_compatible
Previous discussion: #75019
> I think adding a comment saying "This isn't typically the method you want; these addresses don't typically function on modern systems. Use `to_ipv6_mapped` instead." would be a good first step, whether this method gets marked as deprecated or not.
_Originally posted by @joshtriplett in https://github.com/rust-lang/rust/pull/75150#issuecomment-680267745_
Auto merge of #76233 - cuviper:unhasher, r=Mark-Simulacrum
Avoid rehashing Fingerprint as a map key
This introduces a no-op `Unhasher` for map keys that are already hash-
like, for example `Fingerprint` and its wrapper `DefPathHash`. For these
we can directly produce the `u64` hash for maps. The first use of this
is `def_path_hash_to_def_id: Option<UnhashMap<DefPathHash, DefId>>`.
Joshua Nelson [Wed, 2 Sep 2020 03:39:16 +0000 (23:39 -0400)]
Convert many files to intra-doc links
- Use intra-doc links for `std::io` in `std::fs`
- Use intra-doc links for File::read in unix/ext/fs.rs
- Remove explicit intra-doc links for `true` in `net/addr.rs`
- Use intra-doc links in alloc/src/sync.rs
- Use intra-doc links in src/ascii.rs
- Switch to intra-doc links in alloc/rc.rs
- Use intra-doc links in core/pin.rs
- Use intra-doc links in std/prelude
- Use shorter links in `std/fs.rs`
Auto merge of #76160 - scileo:format-recovery, r=petrochenkov
Improve recovery on malformed format call
The token following a format expression should be a comma. However, when it is replaced with a similar token (such as a dot), then the corresponding error is emitted, but the token is treated as a comma, and the parsing step continues.
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