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|
Don't fire `OPAQUE_HIDDEN_INFERRED_BOUND` on sized return of AFIT
Conceptually, we should probably not fire `OPAQUE_HIDDEN_INFERRED_BOUND` for methods like:
```
trait Foo { async fn bar() -> Self; }
```
Even though we technically cannot prove that `Self: Sized`, which is one of the item bounds of the `Output` type in the `-> impl Future<Output = Sized>` from the async desugaring.
This is somewhat justifiable along the same lines as how we allow regular methods to return `-> Self` even though `Self` isn't sized.
Fixes#113538
(side-note: some days i wonder if we should just remove the `OPAQUE_HIDDEN_INFERRED_BOUND` lint... it does make me sad that we have non-well-formed types in signatures, though.)
privacy: Refactor top-level visiting in `NamePrivacyVisitor`
Full hierarchical visiting (`nested_filter::All`) is not necessary, visiting all item-likes in isolation is enough.
Tracking current item is not necessary, passing any `HirId` with the same parent module to `adjust_ident_and_get_scope` is enough.
Follow up to https://github.com/rust-lang/rust/pull/120284.
Remove special-case handling of `vec.split_off(0)`
#76682 added special handling to `Vec::split_off` for the case where `at == 0`. Instead of copying the vector's contents into a freshly-allocated vector and returning it, the special-case code steals the old vector's allocation, and replaces it with a new (empty) buffer with the same capacity.
That eliminates the need to copy the existing elements, but comes at a surprising cost, as seen in #119913. The returned vector's capacity is no longer determined by the size of its contents (as would be expected for a freshly-allocated vector), and instead uses the full capacity of the old vector.
In cases where the capacity is large but the size is small, that results in a much larger capacity than would be expected from reading the documentation of `split_off`. This is especially bad when `split_off` is called in a loop (to recycle a buffer), and the returned vectors have a wide variety of lengths.
I believe it's better to remove the special-case code, and treat `at == 0` just like any other value:
- The current documentation states that `split_off` returns a “newly allocated vector”, which is not actually true in the current implementation when `at == 0`.
- If the value of `at` could be non-zero at runtime, then the caller has already agreed to the cost of a full memcpy of the taken elements in the general case. Avoiding that copy would be nice if it were close to free, but the different handling of capacity means that it is not.
- If the caller specifically wants to avoid copying in the case where `at == 0`, they can easily implement that behaviour themselves using `mem::replace`.
Fixes#119913.
Add portable-atomic-util bug to "bugs found" list
At least, reading https://notgull.net/cautionary-unsafe-tale/ it seems fair to say Miri found this bug. `@notgull` please let me know if you are okay with having this listed here.
Modify GenericArg and Term structs to use strict provenance rules
This is the first PR to solve issue #119217 . In this PR, I have modified the GenericArg struct to use the `NonNull` struct as the pointer instead of `NonZeroUsize`. The change were tested by running `./x test compiler/rustc_middle`.
Resolves https://github.com/rust-lang/rust/issues/119217
r? `@WaffleLapkin`
Replacement of #114390: Add new intrinsic `is_var_statically_known` and optimize pow for powers of two
This adds a new intrinsic `is_val_statically_known` that lowers to [``@llvm.is.constant.*`](https://llvm.org/docs/LangRef.html#llvm-is-constant-intrinsic).` It also applies the intrinsic in the int_pow methods to recognize and optimize the idiom `2isize.pow(x)`. See #114390 for more discussion.
While I have extended the scope of the power of two optimization from #114390, I haven't added any new uses for the intrinsic. That can be done in later pull requests.
Note: When testing or using the library, be sure to use `--stage 1` or higher. Otherwise, the intrinsic will be a noop and the doctests will be skipped. If you are trying out edits, you may be interested in [`--keep-stage 0`](https://rustc-dev-guide.rust-lang.org/building/suggested.html#faster-builds-with---keep-stage).
Fixes#47234Resolves#114390
`@Centri3`
`unescape_literal` becomes `unescape_unicode`, and `unescape_c_string`
becomes `unescape_mixed`. Because rfc3349 will mean that C string
literals will no longer be the only mixed utf8 literals.
`unescape_literal` becomes `unescape_unicode`, and `unescape_c_string`
becomes `unescape_mixed`. Because rfc3349 will mean that C string
literals will no longer be the only mixed utf8 literals.
- Rename it as `MixedUnit`, because it will soon be used in more than
just C string literals.
- Change the `Byte` variant to `HighByte` and use it only for
`\x80`..`\xff` cases. This fixes the old inexactness where ASCII chars
could be encoded with either `Byte` or `Char`.
- Add useful comments.
- Remove `is_ascii`, in favour of `u8::is_ascii`.
- Rename it as `MixedUnit`, because it will soon be used in more than
just C string literals.
- Change the `Byte` variant to `HighByte` and use it only for
`\x80`..`\xff` cases. This fixes the old inexactness where ASCII chars
could be encoded with either `Byte` or `Char`.
- Add useful comments.
- Remove `is_ascii`, in favour of `u8::is_ascii`.
Use upstream exhaustiveness checker!
Because it has been librarified!
The extra `Apache-2.0 WITH LLVM-exception` license is for `rustc_apfloat`. Also this duplicates `rustc_index` because the other upstream deps are still on an earlier version. They should be bumpable now though. Good thing is that we don't need this new crate to be synchronized with the others, which will make our lives easier.
Return a finite number of AllocIds per ConstAllocation in Miri
Before this, every evaluation of a const slice would produce a new AllocId. So in Miri, this program used to have unbounded memory use:
```rust
fn main() {
loop {
helper();
}
}
fn helper() {
"ouch";
}
```
Every trip around the loop creates a new AllocId which we need to keep track of a base address for. And the provenance GC can never clean up that AllocId -> u64 mapping, because the AllocId is for a const allocation which will never be deallocated.
So this PR moves the logic of producing an AllocId for a ConstAllocation to the Machine trait, and the implementation that Miri provides will only produce 16 AllocIds for each allocation. The cache is also keyed on the Instance that the const is evaluated in, so that equal consts evaluated in two functions will have disjoint base addresses.
r? RalfJung
Use `assert_unchecked` instead of `assume` intrinsic in the standard library
Now that a public wrapper for the `assume` intrinsic exists, we can use it in the standard library.
CC #119131
Pack u128 in the compiler to mitigate new alignment
This is based on #116672, adding a new `#[repr(packed(8))]` wrapper on `u128` to avoid changing any of the compiler's size assertions. This is needed in two places:
* `SwitchTargets`, otherwise its `SmallVec<[u128; 1]>` gets padded up to 32 bytes.
* `LitKind::Int`, so that entire `enum` can stay 24 bytes.
* This change definitely has far-reaching effects though, since it's public.
