The feature does not seem to be required by this doctest.

I did some benchmark digging into the `intersperse` and `intersperse_with` code as part of the https://internals.rust-lang.org/t/add-iterate-with-separators-iterator-function/18781/13 discussion, and as a result I optimized them a bit, without relying on the peekable iterator.

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

…ed -Z unstable-options` to shorten symbol names by replacing them with a digest.

Enrich test cases

…st variant

…the layout of type

last usages removed by rust-lang#116170

Co-authored-by: Michael Goulet <michael@errs.io>

When encountering an attribute in a body, we try to recover from an
attribute on an expression (as opposed to a statement). We need to
properly clean up when the attribute is at the end of the body where a
tail expression would be.

Fix rust-lang#118164.

Do not attempt to provide an accurate suggestion for `impl Trait`
in bare trait types when linting. Instead, only do the object
safety check when an E0782 is already going to be emitted in the
2021 edition.

Fix rust-lang#120241.

…iper

Boost iterator intersperse(_with) performance

I did some benchmark digging into the `intersperse` and `intersperse_with` code as part of [this discussion](https://internals.rust-lang.org/t/add-iterate-with-separators-iterator-function/18781/13), and as a result I optimized them a bit, without relying on the peekable iterator.

See also [full benchmark repo](https://github.com/nyurik/intersperse_perf)

Benchmarks show near 2x performance improvements with the simple `sum` [benchmarks](https://gist.github.com/nyurik/68b6c9b3d90f0d14746d4186bf8fa1e2):
![image](https://user-images.githubusercontent.com/1641515/237005195-16aebef4-9eed-4514-8b7c-da1d1f5bd9e0.png)

Properly recover from trailing attr in body

When encountering an attribute in a body, we try to recover from an attribute on an expression (as opposed to a statement). We need to properly clean up when the attribute is at the end of the body where a tail expression would be.

Fix rust-lang#118164, fix rust-lang#118575.

Add the unstable option  to reduce the binary size of dynamic library…

# Motivation

The average length of symbol names in the rust standard library is about 100 bytes, while the average length of symbol names in the C++ standard library is about 65 bytes. In some embedded environments where dynamic library are widely used, rust dynamic library symbol name space hash become one of the key bottlenecks of application, Especially when the existing C/C++ module is reconstructed into the rust module.

The unstable option `-Z symbol_mangling_version=hashed` is added to solve the bottleneck caused by too long dynamic library symbol names.

## Test data

The following is a set of test data on the ubuntu 18.04 LTS environment. With this plug-in, the space saving rate of dynamic libraries can reach about 20%.

The test object is the standard library of rust (built based on Xargo), tokio crate, and hyper crate.

The contents of the Cargo.toml file in the construction project of the three dynamic libraries are as follows:

```txt
# Cargo.toml
[profile.release]
panic = "abort"
opt-leve="z"
codegen-units=1
strip=true
debug=true
```
The built dynamic library also removes the `.rustc` segments that are not needed at run time and then compares the size. The detailed data is as follows:

1. libstd.so
> | symbol_mangling_version | size | saving rate |
> | --- | --- | --- |
> | legacy | 804896 ||
> | hashed | 608288 | 0.244 |
> | v0 | 858144 ||
> | hashed | 608288 | 0.291 |

2. libhyper.so
> | symbol_mangling_version(libhyper.so) | symbol_mangling_version(libstd.so) | size | saving rate |
> | --- | --- | --- | --- |
> | legacy | legacy | 866312 ||
> | hashed | legacy | 645128 |0.255|
> | legacy | hashed | 854024 ||
> | hashed | hashed | 632840 |0.259|

…sDenton

Remove feature not required by `Ipv6Addr::to_cononical` doctest

The feature does not seem to be required by this doctest.

Add FileCheck annotations to dataflow-const-prop tests

part of rust-lang#116971.

A few shadowing variable names are changed, so that it is easier to match the variable names in MIR using FileCheck syntax.

Also, there's a FIXME in [enum.rs](https://github.com/rust-lang/rust/pull/119759/files#diff-7621f55327838e489a95ac99ae1e6126b37c57aff582594e6bee9d7e7e56fc58) because the MIR looks suspicious to me. It has been explained in the comments.

r? cjgillot

…witchs, r=oli-obk

Replace the default branch with an unreachable branch If it is the last variant

Fixes rust-lang#119520.

LLVM currently has limited ability to eliminate dead branches in switches, even with the patch of llvm/llvm-project#73446.

The main reasons are as follows:

- Additional costs are required to calculate the range of values, and there exist many scenarios that cannot be analyzed accurately.
- Matching values by bitwise calculation cannot handle odd branches, nor can it handle values like `-1, 0, 1`. See [SimplifyCFG.cpp#L5424](https://github.com/llvm/llvm-project/blob/llvmorg-17.0.6/llvm/lib/Transforms/Utils/SimplifyCFG.cpp#L5424) and https://llvm.godbolt.org/z/qYMqhvMa8
- The current range information is continuous, even if the metadata for the range is submitted. See [ConstantRange.cpp#L1869-L1870](https://github.com/llvm/llvm-project/blob/llvmorg-17.0.6/llvm/lib/IR/ConstantRange.cpp#L1869-L1870).
- The metadata of the range may be lost in passes such as SROA. See https://rust.godbolt.org/z/e7f87vKMK.

Although we can make improvements, I think it would be more appropriate to put this issue to rustc first. After all, we can easily know the possible values.

Note that we've currently found a slow compilation problem in the presence of unreachable branches. See
llvm/llvm-project#78578.

r? compiler

Avoid ICE in trait without `dyn` lint

Do not attempt to provide an accurate suggestion for `impl Trait` in bare trait types when linting. Instead, only do the object safety check when an E0782 is already going to be emitted in the 2021 edition.

Fix rust-lang#120241.

Update codegen test for LLVM 18

r? `@cuviper`

…ler-errors

ScopeTree: remove destruction_scopes as unused

last usages removed by rust-lang#116170

Unused, but still presented in memory at `t-gmax` (in DHAT termonology)

…piler-errors

Improve handling of numbers in `IntoDiagnosticArg`

While working on rust-lang#120393, I realize that my fluent selectors were not working. So here is an improvement (not a fix unfortunately).

…rieb

Remove myself from review rotation

Still willing to do reviews (and make it through my backlog), but I don't have the bandwidth to be on the rotation right now.