Previously checking for `pmoda == 0` would get LLVM to generate branchy
code, when, for `stride = 1` the offset can be computed without such a
branch by doing effectively a `-p % a`.
For well-known (constant) alignments, with the new ordering of these
conditionals, we end up generating 2 to 3 cheap instructions on x86_64:
movq %rdi, %rax
negl %eax
andl $7, %eax
instead of 5+ as previously.
For unknown alignments the new code also generates just 3 instructions:
negq %rdi
leaq -1(%rsi), %rax
andq %rdi, %rax
At opt-level <= 1, the methods such as `wrapping_mul` are not being
inlined, causing significant bloating and slowdowns of the
implementation at these optimisation levels.
With use of these intrinsics, the codegen of this function at
-Copt_level=1 is the same as it is at -Copt_level=3.
In the current documentation about the `Copy` marker trait, there is a section
with examples of structs that can implement `Copy`. Currently there is no example for
showing that shared references (`&T`) are also `Copy`.
It is worth to have a dedicated example for `&T` being `Copy`, because shared
references are an integral part of the language and it being `Copy` is not as
intuitive as other types that share this behaviour like `i32` or `bool`.
The example picks up on the previous non-`Copy` struct and shows that
structs can be `Copy`, even when they hold a shared reference to a non-`Copy` type.
This commit adds new lang items which will be used in AST lowering once
`QPath::LangItem` is introduced.
Co-authored-by: Matthew Jasper <mjjasper1@gmail.com>
Signed-off-by: David Wood <david@davidtw.co>
Move to intra doc links in std::net
Helps with #75080.
@rustbot modify labels: T-doc, A-intra-doc-links, T-rustdoc
The links for `true` and `false` had to stay else `rustdoc` complained, it is intended ?
Doc: String isn't a collection
On forums one user was confused by this text, interpreting it as saying that `String` is a `Vec<char>` literally, rather than figuratively for the purpose of collect. I've reworded that paragraph.
Switch to intra-doc links in `core::option`
Part of #75080.
I didn't change some of the links since they link into `std` and you can't link from `core` to `std` (#74481).
Also, at least one other link can't be switched to an intra-doc link because it's not supported yet (#74489).
Add sanitizer support on FreeBSD
Restarting #47337. Everything is better now, no more weird llvm problems, well not everything:
Unfortunately, the sanitizers don't have proper support for versioned symbols (https://github.com/google/sanitizers/issues/628), so `libc`'s usage of `stat@FBSD_1.0` and so on explodes, e.g. in calling `std::fs::metadata`.
Building std (now easy thanks to cargo `-Zbuild-std`) and libc with `freebsd12/13` config via the `LIBC_CI=1` env variable is a good workaround…
```
LIBC_CI=1 RUSTFLAGS="-Z sanitizer=address" cargo +san-test -Zbuild-std run --target x86_64-unknown-freebsd --verbose
```
…*except* std won't build because there's no `st_lspare` in the ino64 version of the struct, so an std patch is required:
```diff
--- i/src/libstd/os/freebsd/fs.rs
+++ w/src/libstd/os/freebsd/fs.rs
@@ -66,8 +66,6 @@ pub trait MetadataExt {
fn st_flags(&self) -> u32;
#[stable(feature = "metadata_ext2", since = "1.8.0")]
fn st_gen(&self) -> u32;
- #[stable(feature = "metadata_ext2", since = "1.8.0")]
- fn st_lspare(&self) -> u32;
}
#[stable(feature = "metadata_ext", since = "1.1.0")]
@@ -136,7 +134,4 @@ impl MetadataExt for Metadata {
fn st_flags(&self) -> u32 {
self.as_inner().as_inner().st_flags as u32
}
- fn st_lspare(&self) -> u32 {
- self.as_inner().as_inner().st_lspare as u32
- }
}
```
I guess std could like.. detect that `libc` isn't built for the old ABI, and replace the implementation of `st_lspare` with a panic?
Revert the fundamental changes in #74762 and #75257
Before possibly going over to #75487. Also contains some added and fixed comments.
r? @Mark-Simulacrum
std/sys/unix/time: make it easier for LLVM to optimize `Instant` subtraction.
This PR is the minimal change necessary to get LLVM to optimize `if self.t.tv_nsec >= other.t.tv_nsec` to branchless instructions (at least on x86_64), inspired by @m-ou-se's own attempts at optimizing `Instant` subtraction.
I stumbled over this by looking at the total number of instructions executed by `rustc -Z self-profile`, and found that after disabling ASLR, the largest source of non-determinism remaining was from this `if` taking one branch or the other, depending on the values involved.
The reason this code is even called so many times to make a difference, is that `measureme` (the `-Z self-profile` implementation) currently uses `Instant::elapsed` for its event timestamps (of which there can be millions).
I doubt it's critical to land this, although perhaps it could slightly improve some forms of benchmarking.
Migrate unit tests of btree collections to their native breeding ground
There's one BTreeSet test case that I couldn't easily convince to come along, maybe because it truly is an integration test. But leaving it in place would mean git wouldn't see the move so I also moved it to a new file.
r? @Mark-Simulacrum
BTreeMap: purge innocent use of into_kv_mut
Replace the use of `into_kv_mut` into more precise calls. This makes more sense if you know that the single remaining use of `into_kv_mut` is in fact evil and can be trialled in court (#75200) and sent to a correction facility (#73971).
No real performance difference reported (but functions that might benefit a tiny constant bit like `BTreeMap::get_mut` aren't benchmarked):
```
benchcmp old new --threshold 5
name old ns/iter new ns/iter diff ns/iter diff % speedup
btree::map::clone_fat_100 63,073 59,256 -3,817 -6.05% x 1.06
btree::map::iter_100 3,514 3,235 -279 -7.94% x 1.09
```
Change Debug impl of SocketAddr and IpAddr to match their Display output
This has already been done for `SocketAddrV4`, `SocketAddrV6`, `IpAddrV4` and `IpAddrV6`. I don't see a point to keep the rather bad to read derived impl, especially so when pretty printing:
V4(
127.0.0.1
)
From the `Display`, one can easily and unambiguously see if it's V4 or V6. Two examples:
```
127.0.0.1:443
[2001:db8:85a3::8a2e:370:7334]:443
```
Luckily the docs explicitly state that `Debug` output is not stable and that it may be changed at any time.
Using `Display` as `Debug` is very convenient for configuration structs (e.g. for webservers) that often just have a `derive(Debug)` and are printed that way to the one starting the server.
Improve documentation on process::Child.std* fields
As a relative beginner, it took a while for me to figure out I could just steal the references to avoid partially moving the child and thus retain ability to call functions on it (and store it in structs etc).
