… previously in the unstable core::num::Float trait.
Per https://github.com/rust-lang/rust/issues/32110#issuecomment-379503183,
the `abs`, `signum`, and `powi` methods are *not* included for now
since they rely on LLVM intrinsics and we haven’t determined yet whether
those instrinsics lower to calls to libm functions on any platform.
Inline most of the code paths for conversions with boxed slices
This helps with the specific problem described in #49541, obviously without making any large change to how inlining works in the general case.
Everything involved in the conversions is made `#[inline]`, except for the `<Vec<T>>::into_boxed_slice` entry point which is made `#[inline(always)]` after checking that duplicating the function mentioned in the issue prevented its inlining if I only annotate it with
`#[inline]`.
For the record, that function was:
```rust
pub fn foo() -> Box<[u8]> {
vec![0].into_boxed_slice()
}
```
To help the inliner's job, we also hoist a `self.capacity() != self.len` check in `<Vec<T>>::shrink_to_fit` and mark it as `#[inline]` too.
Replace manual iterator exhaust with for_each(drop)
This originally added a dedicated method, `Iterator::exhaust`, and has since been replaced with `for_each(drop)`, which is more idiomatic.
<del>This is just shorthand for `for _ in &mut self {}` or `while let Some(_) = self.next() {}`. This states the intent a lot more clearly than the identical code: run the iterator to completion.
<del>At least personally, my eyes tend to gloss over `for _ in &mut self {}` without fully paying attention to what it does; having a `Drop` implementation akin to:
<del>`for _ in &mut self {}; unsafe { free(self.ptr); }`</del>
<del>Is not as clear as:
<del>`self.exhaust(); unsafe { free(self.ptr); }`
<del>Additionally, I've seen debate over whether `while let Some(_) = self.next() {}` or `for _ in &mut self {}` is more clear, whereas `self.exhaust()` is clearer than both.
Some modules were still using the deprecated `allocator` module, use the
`alloc` module instead.
Some modules were using `super` while it's not needed.
Some modules were more or less ordering them, and other not, so the
latter have been modified to match the others.
Deprecate offset_to; switch core&alloc to using offset_from instead
Bonus: might make code than uses `.len()` on slice iterators faster
cc https://github.com/rust-lang/rust/issues/41079
Add more vec![... ; n] optimizations
vec![0; n], via implementations of SpecFromElem, has an optimization that uses with_capacity_zeroed instead of with_capacity, which will use calloc instead of malloc, and avoid an extra memset.
This PR adds the same optimization for ptr::null, ptr::null_mut, and None, when their in-memory representation is zeroes.
Introduce Vec::resize_with method (see #41758)
In #41758, the libs team decided they preferred `Vec::resize_with` over `Vec::resize_default()`. Here is an implementation to get this moving forward.
I don't know what the removal process for `Vec::resize_default()` should be, so I've left it in place for now. Would be happy to follow up with its removal.
vec![0; n], via implementations of SpecFromElem, has an optimization
that uses with_capacity_zeroed instead of with_capacity, which will use
calloc instead of malloc, and avoid an extra memset.
This adds the same optimization for vec![ptr::null(); n] and
vec![ptr::null_mut(); n], assuming their bit value is 0 (which is true
on all currently supported platforms).
This does so by adding an intermediate trait IsZero, which looks very
much like nonzero::Zeroable, but that one is on the way out, and doesn't
apply to pointers anyways.
Adding such a trait allows to avoid repeating the logic using
with_capacity_zeroed or with_capacity, or making the macro more complex
to support generics.
This helps with the specific problem described in #49541, obviously without
making any large change to how inlining works in the general case.
Everything involved in the conversions is made `#[inline]`, except for the
`<Vec<T>>::into_boxed_slice` entry point which is made `#[inline(always)]`
after checking that duplicating the function mentioned in the issue prevented
its inlining if I only annotate it with `#[inline]`.
For the record, that function was:
```rust
pub fn foo() -> Box<[u8]> {
vec![0].into_boxed_slice()
}
```
To help the inliner's job, we also hoist a `self.capacity() != self.len` check
in `<Vec<T>>::shrink_to_fit` and mark it as `#[inline]` too.
Use f{32,64}::to_bits for is_zero test in vec::SpecFromElem
vec::SpecFromElem provides an optimization to use calloc to fill a Vec
when the element given to fill the Vec is represented by 0.
For floats, the test for that currently used is `x == 0. &&
x.is_sign_positive()`. When compiled in a standalone function, rustc
generates the following assembly:
```
xorps xmm1, xmm1
ucomisd xmm0, xmm1
setnp al
sete cl
and cl, al
movq rax, xmm0
test rax, rax
setns al
and al, cl
ret
```
A simpler test telling us whether the value is represented by 0, is
`x.to_bits() == 0`, which rustc compiles to:
```
movq rax, xmm0
test rax, rax
sete al
ret
```
Not that the test is hot in any way, but it also makes it clearer what
the intent in the rust code is.
vec::SpecFromElem provides an optimization to use calloc to fill a Vec
when the element given to fill the Vec is represented by 0.
For floats, the test for that currently used is `x == 0. &&
x.is_sign_positive()`. When compiled in a standalone function, rustc
generates the following assembly:
```
xorps xmm1, xmm1
ucomisd xmm0, xmm1
setnp al
sete cl
and cl, al
movq rax, xmm0
test rax, rax
setns al
and al, cl
ret
```
A simpler test telling us whether the value is represented by 0, is
`x.to_bits() == 0`, which rustc compiles to:
```
movq rax, xmm0
test rax, rax
sete al
ret
```
Not that the test is hot in any way, but it also makes it clearer what
the intent in the rust code is.
Stabilize FusedIterator
FusedIterator is a marker trait that promises that the implementing
iterator continues to return `None` from `.next()` once it has returned
`None` once (and/or `.next_back()`, if implemented).
The effects of FusedIterator are already widely available through
`.fuse()`, but with stable `FusedIterator`, stable Rust users can
implement this trait for their iterators when appropriate.
Closes#35602
FusedIterator is a marker trait that promises that the implementing
iterator continues to return `None` from `.next()` once it has returned
`None` once (and/or `.next_back()`, if implemented).
The effects of FusedIterator are already widely available through
`.fuse()`, but with stable `FusedIterator`, stable Rust users can
implement this trait for their iterators when appropriate.
The docs currently say, "If the closure returns false, it will try
again, and call the closure on the next element." But this happens
regardless of whether the closure returns true or false.
Make core::ops::Place an unsafe trait
Consumers of `Place` would reasonably expect that the `pointer` function returns a valid pointer to memory that can actually be written to.
After discussing [1] today with @pnkfelix and @Gankro,
we concluded that it’s ok for drop checking not to be much smarter
than the current `#[may_dangle]` design which requires an explicit
unsafe opt-in.
[1] https://github.com/rust-lang/rust/issues/27730#issuecomment-316432083
Many AsciiExt imports have become useless thanks to the inherent ascii
methods added in the last commits. These were removed. In some places, I
fully specified the ascii method being called to enforce usage of the
AsciiExt trait. Note that some imports are not removed but tagged with
a `#[cfg(stage0)]` attribute. This is necessary, because certain ascii
methods are not yet available in stage0. All those imports will be
removed later.
Additionally, failing tests were fixed. The test suite should exit
successfully now.
