When `x` has large magnitude, `x + ((x * x) + 1.0).sqrt()` approaches
`x + x.abs()`. For negative values of `x`, this leads to catastrophic
cancellation, resulting in large errors or even 0 being passed to
`ln`, producing incorrect results including `-inf`.

Becuase asinh is an odd function, i.e. -asinh(x) = asinh(-x) for all
x, we can avoid the catastrophic cancellation and obtain correct
results by taking the absolute value of `self` for the first
term. `self * self` is always positive, so in effect this gives us
`x.abs().asinh().copysign(x)` which as discussed above is
algebraically equivalent, but is much more accurate.

This isn't sound without validation. We don't want to report errors in case of failure to intern and validate, we just don't want to const prop. Interning and const prop is not built for this, let's not do it until we have a clearer picture on aggregate propagation.

Closes rust-lang#72679
Closes rust-lang#72372
Closes rust-lang#72285

`crt-static` is a rust specific target feature that's absent from llvm feature table, adding it there.

Fixes: rust-lang#70693

Co-authored-by: lzutao <taolzu@gmail.com>

Separate target features from rust ones with a blank line

Co-authored-by: Josh Stone <cuviper@gmail.com>

…tion

We only need to cast the pointer once to change `Box<T>` to an array
`Box<[T; 1]>`, then we can let unsized coercion return `Box<[T]>`.

Enabling static-pie for musl

and make it the default for the x86_64-unknown-linux-musl target

This is a quick implementation for rust-lang#70693

Opening it as a draft PR to gather some feedback, before I put more work in it.

```console
❯ cat hello.rs
fn main() {
    println!("main = {:#x}", &main as *const _ as usize);
}

❯  /tmp/rust-musl/bin/rustc  --target x86_64-unknown-linux-musl  ~/hello.rs

❯ ldd hello
	statically linked

❯ file hello
hello: ELF 64-bit LSB shared object, x86-64, version 1 (GNU/Linux), statically linked, BuildID[sha1]=fec5cdc170f503a712a63a6958691ce5ce433654, with debug_info, not stripped

❯ ./hello
main = 0x7f233ca30008

❯ ./hello
main = 0x7f9ddc529008

❯ ./hello
main = 0x7f1e5a224008

❯ ./hello
main = 0x7f4485c7c008

❯ /tmp/rust-musl/bin/rustc  --target x86_64-unknown-linux-musl  -Z print-link-args  ~/hello.rs
"cc" "-Wl,--as-needed" "-Wl,-z,noexecstack" "-Wl,--eh-frame-hdr" "-m64" "-nostdlib" "/tmp/rust-musl/lib/rustlib/x86_64-unknown-linux-musl/lib/rcrt1.o" "/tmp/rust-musl/lib/rustlib/x86_64-unknown-linux-musl/lib/crti.o" "-L" "/tmp/rust-musl/lib/rustlib/x86_64-unknown-linux-musl/lib" "hello.hello.7rcbfp3g-cgu.0.rcgu.o" "hello.hello.7rcbfp3g-cgu.1.rcgu.o" "hello.hello.7rcbfp3g-cgu.2.rcgu.o" "hello.hello.7rcbfp3g-cgu.3.rcgu.o" "hello.hello.7rcbfp3g-cgu.4.rcgu.o" "hello.hello.7rcbfp3g-cgu.5.rcgu.o" "-o" "hello" "hello.1nxjf9so94czdgcz.rcgu.o" "-Wl,--gc-sections" "-static-pie" "-Wl,-zrelro" "-Wl,-znow" "-nodefaultlibs" "-L" "/tmp/rust-musl/lib/rustlib/x86_64-unknown-linux-musl/lib" "-Wl,--start-group" "-Wl,-Bstatic" "/tmp/rust-musl/lib/rustlib/x86_64-unknown-linux-musl/lib/libstd-0f9cb7646f9e2c34.rlib" "/tmp/rust-musl/lib/rustlib/x86_64-unknown-linux-musl/lib/libpanic_unwind-ba857f2f2e4e7187.rlib" "/tmp/rust-musl/lib/rustlib/x86_64-unknown-linux-musl/lib/libhashbrown-58ba5e25bbdf9d29.rlib" "/tmp/rust-musl/lib/rustlib/x86_64-unknown-linux-musl/lib/librustc_std_workspace_alloc-886bfe43afa847dc.rlib" "/tmp/rust-musl/lib/rustlib/x86_64-unknown-linux-musl/lib/libbacktrace-fbfb8fe99f19a67b.rlib" "/tmp/rust-musl/lib/rustlib/x86_64-unknown-linux-musl/lib/libbacktrace_sys-85fa859e7d364cc9.rlib" "/tmp/rust-musl/lib/rustlib/x86_64-unknown-linux-musl/lib/librustc_demangle-07ab026cd3ec0d82.rlib" "/tmp/rust-musl/lib/rustlib/x86_64-unknown-linux-musl/lib/libunwind-a8ec5932d92ea864.rlib" "/tmp/rust-musl/lib/rustlib/x86_64-unknown-linux-musl/lib/libcfg_if-0ba4cc2f38a198d5.rlib" "/tmp/rust-musl/lib/rustlib/x86_64-unknown-linux-musl/lib/liblibc-c1bb2b3ce4f78b7c.rlib" "/tmp/rust-musl/lib/rustlib/x86_64-unknown-linux-musl/lib/liballoc-0ff673c1cf0d451a.rlib" "/tmp/rust-musl/lib/rustlib/x86_64-unknown-linux-musl/lib/librustc_std_workspace_core-c8ff2001db856926.rlib" "/tmp/rust-musl/lib/rustlib/x86_64-unknown-linux-musl/lib/libcore-2ae14177140eeca2.rlib" "-Wl,--end-group" "/tmp/rust-musl/lib/rustlib/x86_64-unknown-linux-musl/lib/libcompiler_builtins-4fd81b5ce1b08a9c.rlib" "-static" "-Wl,-Bdynamic" "/tmp/rust-musl/lib/rustlib/x86_64-unknown-linux-musl/lib/crtn.o"
```

Closes rust-lang#70693
Closes rust-lang#53968

…ing-drop, r=matthewjasper,nikomatsakis

Report error when casting an C-like enum implementing Drop

Following approach described in rust-lang#35941

Fix asinh of negative values

Rust's current implementation of asinh has [large errors](https://www.wolframalpha.com/input/?i=arcsinh%28x%29%2C+ln%28x%2B%28x%5E2%2B1%29%5E0.5%29%2C+x+from+-67452095.07139316+to+0) in its negative range. ~These are (mostly) not numerical, but rather seem due to an incorrect implementation.~ This appears to be due to avoidable catastrophic cancellation.
[Playground before/after](https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=bd04ae6d86d06612e4e389a8b95d19ab).
[glibc uses](https://github.com/bminor/glibc/blob/81dca813cc35f91414731fdd0ff6b756d5e1827f/sysdeps/ieee754/dbl-64/s_asinh.c#L56) abs here.

Many thanks to @danieldeankon for finding this weird behavior, @jebrosen for diagnosing it, and @toasteater for identifying the probable implementation error!

tag/niche terminology cleanup

The term "discriminant" was used in two ways throughout the compiler:
* every enum variant has a corresponding discriminant, that can be given explicitly with `Variant = N`.
* that discriminant is then encoded in memory to store which variant is active -- but this encoded form of the discriminant was also often called "discriminant", even though it is conceptually quite different (e.g., it can be smaller in size, or even use niche-filling).

After discussion with @eddyb, this renames the second term to "tag". The way the tag is encoded can be either `TagEncoding::Direct` (formerly `DiscriminantKind::Tag`) or `TagEncoding::Niche` (formerly `DiscrimianntKind::Niche`).

This finally resolves some long-standing confusion I had about the handling of variant indices and discriminants, which surfaced in rust-lang#72419.

(There is also a `DiscriminantKind` type in libcore, it remains unaffected. I think this corresponds to the discriminant, not the tag, so that seems all right.)

r? @eddyb

…, r=Mark-Simulacrum

Create self-contained directory and move there some of external binaries/libs

One of the steps to reach design described in rust-lang#68887 (comment)
This PR moves things around and allows link code to handle the new directory structure.

…ndirects, r=oli-obk

Remove const prop for indirects

This was only used by one mir-opt test and since it causes buggy behavior under `-Zmir-opt-level=2`, it seems like we should remove it.

This was split out from rust-lang#71946.

Closes rust-lang#72679
Closes rust-lang#72372
Closes rust-lang#72285

Ensure std benchmarks get tested.

This ensures that the std benchmarks don't break in the future. Currently they aren't compiled or tested on CI, so they can easily bitrot.  Testing a benchmark runs it with one iteration. Adding these should only add a few seconds to CI.

Closes rust-lang#54176
Closes rust-lang#61913

… r=petrochenkov

Disallow loading crates with non-ascii identifier name.

This turns off external crate loading with non-ascii identifier names.

cc rust-lang#55467.

Add rust specific features to print target features

Fixes rust-lang#71583

`crt-static` is a rust specific target feature that's absent from llvm feature table, adding it there so that it shows under `rustc --print target-features`.

Probably the most native implementation I could think of, would love to get feedback.

Test that bounds checks are elided when slice len is checked up-front

Closes rust-lang#69101

…=dtolnay

Reduce pointer casts in Box::into_boxed_slice

We only need to cast the pointer once to change `Box<T>` to an array
`Box<[T; 1]>`, then we can let unsized coercion return `Box<[T]>`.

… r=jonas-schievink

Document format correction

Minor amendments to the document.

r? @steveklabnik

Minor tweaks to liballoc