enable Atomic*.{load,store} for ARMv6-M / MSP430
closes#45085
as proposed in https://github.com/rust-lang/rust/issues/45085#issuecomment-384825434
this commit adds an `atomic_cas` target option and extends the `#[cfg(target_has_atomic)]`
attribute to enable a subset of the `Atomic*` API on architectures that don't support atomic CAS
natively, like MSP430 and ARMv6-M.
r? @alexcrichton
Any docs preposition change
This changes the docs referring to where a user should be wary of depending on "Any" trait impls from warning about relying on them "outside" of their code to warning about relying on them "inside" of their code.
closes#45085
this commit adds an `atomic_cas` target option and an unstable `#[cfg(target_has_atomic_cas)]`
attribute to enable a subset of the `Atomic*` API on architectures that don't support atomic CAS
natively, like MSP430 and ARMv6-M.
Unpin references
I also considered adding an impl for raw pointers as well, but that makes it easy to accidentally have unsound owning-collections that might otherwise be able to project pinned-ness (e.g. `Box`).
cc @RalfJung
r? @withoutboats
This changes the docs referring to where a user should be wary of depending on "Any" trait impls from warning about relying on them "outside" of their code to warning about relying on them "inside" of their code.
Implement always-fallible TryFrom for usize/isize conversions that are infallible on some platforms
This reverts commit 837d6c7023 "Remove TryFrom impls that might become conditionally-infallible with a portability lint".
This fixes#49415 by adding (restoring) missing `TryFrom` impls for integer conversions to or from `usize` or `isize`, by making them always fallible at the type system level (that is, with `Error=TryFromIntError`) even though they happen to be infallible on some platforms (for some values of `size_of::<usize>()`).
They had been removed to allow the possibility to conditionally having some of them be infallible `From` impls instead, depending on the platforms, and have the [portability lint](https://github.com/rust-lang/rfcs/pull/1868) warn when they are used in code that is not already opting into non-portability. For example `#[allow(some_lint)] usize::from(x: u64)` would be valid on code that only targets 64-bit platforms.
This PR gives up on this possiblity for two reasons:
* Based on discussion with @aturon, it seems that the portability lint is not happening any time soon. It’s better to have the conversions be available *at all* than keep blocking them for so long. Portability-lint-gated platform-specific APIs can always be added separately later.
* For code that is fine with fallibility, the alternative would force it to opt into "non-portability" even though there would be no real portability issue.
Fix some doc links
The futures crate CI always fails because of these intra doc links. I hope that this will fix this issue.
r? @steveklabnik
@cramertj
Edit: I added @steveklabnik as reviewer because this PR also adjusts a link in `src/libstd/error.rs`
Stabilize Iterator::flatten in 1.29, fixes#48213.
This PR stabilizes [`Iterator::flatten`](https://doc.rust-lang.org/nightly/std/iter/trait.Iterator.html#method.flatten) in *version 1.29* (1.28 goes to beta in 10 days, I don't think there's enough time to land it in that time, but let's see...).
Tracking issue is: #48213.
cc @bluss re. itertools.
r? @SimonSapin
ping @pietroalbini -- let's do a crater run when this passes CI :)
Use assert_eq! in copy_from_slice
This will print both lengths when the assertion fails instead of just saying that they're different.
Output of current stable and nightly (modulo the exact line number):
```
thread 'main' panicked at 'destination and source slices have different lengths', libcore/slice/mod.rs:1645:9
```
Output after this PR:
```
thread 'main' panicked at 'assertion failed: `(left == right)`
left: `123`,
right: `456`: destination and source slices have different lengths', libcore/slice/mod.rs:1645:9
```
Note that I have not run the tests locally.
Optimize RefCell refcount tracking
Address the performance concern raised in https://github.com/rust-lang/rust/pull/51466#issuecomment-398255276
cc @dtolnay @nnethercote @rust-lang/wg-compiler-performance
cc @RalfJung @jhjourdan for soundness concerns
Can somebody kick off a perf run on this? I'm not sure how that's done, but I understand it has to be started manually.
The idea of this change is to switch to representing mutable refcount as values below 0 to eliminate some branching that was required with the old algorithm.
Document round-off error in `.mod_euc()`-method, see issue #50179
Due to a round-off error the method `.mod_euc()` of both `f32` and `f64` can produce mathematical invalid outputs. If `self` in magnitude is much small than the modulus `rhs` and negative, `self + rhs` in the first branch cannot be represented in the given precision and results into `rhs`. In the mathematical strict sense, this breaks the definition. But given the limitation of floating point arithmetic it can be thought of the closest representable value to the true result, although it is not strictly in the domain `[0.0, rhs)` of the function. It is rather the left side asymptotical limit. It would be desirable that it produces the mathematical more sound approximation of `0.0`, the right side asymptotical limit. But this breaks the property, that `self == self.div_euc(rhs) * rhs + a.mod_euc(rhs)`.
The discussion in issue #50179 did not find an satisfying conclusion to which property is deemed more important. But at least we can document the behaviour. Which this pull request does.
Optimize sum of Durations by using custom function
The current `impl Sum for Duration` uses `fold` to perform several `add`s (or really `checked_add`s) of durations. In doing so, it has to guarantee the number of nanoseconds is valid after every addition. If you squeese the current implementation into a single function it looks kind of like this:
````rust
fn sum<I: Iterator<Item = Duration>>(iter: I) -> Duration {
let mut sum = Duration::new(0, 0);
for rhs in iter {
if let Some(mut secs) = sum.secs.checked_add(rhs.secs) {
let mut nanos = sum.nanos + rhs.nanos;
if nanos >= NANOS_PER_SEC {
nanos -= NANOS_PER_SEC;
if let Some(new_secs) = secs.checked_add(1) {
secs = new_secs;
} else {
panic!("overflow when adding durations");
}
}
sum = Duration { secs, nanos }
} else {
panic!("overflow when adding durations");
}
}
sum
}
````
We only need to check if `nanos` is in the correct range when giving our final answer so we can have a more optimized version like so:
````rust
fn sum<I: Iterator<Item = Duration>>(iter: I) -> Duration {
let mut total_secs: u64 = 0;
let mut total_nanos: u64 = 0;
for entry in iter {
total_secs = total_secs
.checked_add(entry.secs)
.expect("overflow in iter::sum over durations");
total_nanos = match total_nanos.checked_add(entry.nanos as u64) {
Some(n) => n,
None => {
total_secs = total_secs
.checked_add(total_nanos / NANOS_PER_SEC as u64)
.expect("overflow in iter::sum over durations");
(total_nanos % NANOS_PER_SEC as u64) + entry.nanos as u64
}
};
}
total_secs = total_secs
.checked_add(total_nanos / NANOS_PER_SEC as u64)
.expect("overflow in iter::sum over durations");
total_nanos = total_nanos % NANOS_PER_SEC as u64;
Duration {
secs: total_secs,
nanos: total_nanos as u32,
}
}
````
We now only convert `total_nanos` to `total_secs` (1) if `total_nanos` overflows and (2) at the end of the function when we have to output a valid `Duration`. This gave a 5-22% performance improvement when I benchmarked it, depending on how big the `nano` value of the `Duration`s in `iter` were.
lint to favor `..=` over `...` range patterns; migrate to `..=` throughout codebase
We probably need an RFC to actually deprecate the `...` syntax, but here's a candidate implementation for the lint considered in #51043. (My local build is super flaky, but hopefully I got all of the test revisions.)
New safe associated functions for PinMut
- Add safe `get_mut` and `map`
- Rename unsafe equivalents to `get_mut_unchecked` and `map_unchecked`
The discussion about this starts [in this comment](https://github.com/rust-lang/rust/issues/49150#issuecomment-399604573) on the tracking issue.
Option::get_or_insert(_with): Replace unreachable! with unreachable_unchecked
Optimize codegen for both functions as the None branch is trivially not reachable.
Various changes to existing diagnostics
* [Add code to `invalid ABI` error, add span label, move list to help to make message shorter](https://github.com/rust-lang/rust/pull/51463/commits/23ae5af274defa9ff884f593e44a2bbcaf814a02):
```
error[E0697]: invalid ABI: found `路濫狼á́́`
--> $DIR/unicode.rs:11:8
|
LL | extern "路濫狼á́́" fn foo() {} //~ ERROR invalid ABI
| ^^^^^^^^^ invalid ABI
|
= help: valid ABIs: cdecl, stdcall, fastcall, vectorcall, thiscall, aapcs, win64, sysv64, ptx-kernel, msp430-interrupt, x86-interrupt, Rust, C, system, rust-intrinsic, rust-call, platform-intrinsic, unadjusted
```
* [Add code to incorrect `pub` restriction error](https://github.com/rust-lang/rust/pull/51463/commits/e96fdea8a38f39f99f8b9a4000a689187a457e08)
* [Add message to `rustc_on_unimplemented` attributes in core to have them set a custom message _and_ label](https://github.com/rust-lang/rust/pull/51463/commits/2cc7e5ed307aee936c20479cfdc7409d6b52a464):
```
error[E0277]: `W` does not have a constant size known at compile-time
--> $DIR/unsized-enum2.rs:33:8
|
LL | VA(W),
| ^ `W` does not have a constant size known at compile-time
|
= help: the trait `std::marker::Sized` is not implemented for `W`
= help: consider adding a `where W: std::marker::Sized` bound
= note: no field of an enum variant may have a dynamically sized type
```
```
error[E0277]: `Foo` cannot be sent between threads safely
--> $DIR/E0277-2.rs:26:5
|
LL | is_send::<Foo>();
| ^^^^^^^^^^^^^^ `Foo` cannot be sent between threads safely
|
= help: the trait `std::marker::Send` is not implemented for `Foo`
```
```
error[E0277]: can't compare `{integer}` with `std::string::String`
--> $DIR/binops.rs:16:7
|
LL | 5 < String::new();
| ^ no implementation for `{integer} < std::string::String` and `{integer} > std::string::String`
|
= help: the trait `std::cmp::PartialOrd<std::string::String>` is not implemented for `{integer}`
```
```
error[E0277]: can't compare `{integer}` with `std::result::Result<{integer}, _>`
--> $DIR/binops.rs:17:7
|
LL | 6 == Ok(1);
| ^^ no implementation for `{integer} == std::result::Result<{integer}, _>`
|
= help: the trait `std::cmp::PartialEq<std::result::Result<{integer}, _>>` is not implemented for `{integer}`
```
```
error[E0277]: a collection of type `i32` cannot be built from an iterator over elements of type `i32`
--> $DIR/type-check-defaults.rs:16:19
|
LL | struct WellFormed<Z = Foo<i32, i32>>(Z);
| ^ a collection of type `i32` cannot be built from `std::iter::Iterator<Item=i32>`
|
= help: the trait `std::iter::FromIterator<i32>` is not implemented for `i32`
note: required by `Foo`
--> $DIR/type-check-defaults.rs:15:1
|
LL | struct Foo<T, U: FromIterator<T>>(T, U);
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
```
* [Add link to book for `Sized` errors](https://github.com/rust-lang/rust/pull/51463/commits/1244dc7c283323aea1a3457a4458d590a3e160c8):
```
error[E0277]: `std::fmt::Debug + std::marker::Sync + 'static` does not have a constant size known at compile-time
--> $DIR/const-unsized.rs:13:29
|
LL | const CONST_0: Debug+Sync = *(&0 as &(Debug+Sync));
| ^^^^^^^^^^^^^^^^^^^^^^ `std::fmt::Debug + std::marker::Sync + 'static` does not have a constant size known at compile-time
|
= help: the trait `std::marker::Sized` is not implemented for `std::fmt::Debug + std::marker::Sync + 'static`
= note: to learn more, visit <https://doc.rust-lang.org/book/second-edition/ch19-04-advanced-types.html#dynamically-sized-types--sized>
= note: constant expressions must have a statically known size
```
* [Point to previous line for single expected token not found](https://github.com/rust-lang/rust/pull/51463/commits/48165168fb0f059d8536cd4a2276b609d4a7f721) (if the current token is in a different line)
Specialize StepBy<Range(Inclusive)>
Part of #51557, related to #43064, #31155
As discussed in the above issues, `step_by` optimizes very badly on ranges which is related to
1. the special casing of the first `StepBy::next()` call
2. the need to do 2 additions of `n - 1` and `1` inside the range's `next()`
This PR eliminates both by overriding `next()` to always produce the current element and also step ahead by `n` elements in one go. The generated code is much better, even identical in the case of a `Range` with constant `start` and `end` where `start+step` can't overflow. Without constant bounds it's a bit longer than the manual loop. `RangeInclusive` doesn't optimize as nicely but is still much better than the original asm.
Unsigned integers optimize better than signed ones for some reason.
See the following two links for a comparison.
[godbolt: specialization for ..](https://godbolt.org/g/haHLJr)
[godbolt: specialization for ..=](https://godbolt.org/g/ewyMu6)
`RangeFrom`, the only other range with an `Iterator` implementation can't be specialized like this without changing behaviour due to overflow. There is no way to save "finished-ness".
The approach can not be used in general, because it would produce side effects of the underlying iterator too early.
May obsolete #51435, haven't checked.
