Implement MIR lowering for unsafe binders
This is the final bit of the unsafe binders puzzle. It implements MIR, CTFE, and codegen for unsafe binders, and enforces that (for now) they are `Copy`. Later on, I'll introduce a new trait that relaxes this requirement to being "is `Copy` or `ManuallyDrop<T>`" which more closely models how we treat union fields.
Namely, wrapping unsafe binders is now `Rvalue::WrapUnsafeBinder`, which acts much like an `Rvalue::Aggregate`. Unwrapping unsafe binders are implemented as a MIR projection `ProjectionElem::UnwrapUnsafeBinder`, which acts much like `ProjectionElem::Field`.
Tracking:
- https://github.com/rust-lang/rust/issues/130516
miri: optimize zeroed alloc
When allocating zero-initialized memory in MIR interpretation, rustc allocates zeroed memory, marks it as initialized and then re-zeroes it. Remove the last step.
I don't expect this to have much of an effect on performance normally, but in my case in which I'm creating a large allocation via mmap it gets in the way.
This renames variables named `str` to other names, to make sure `str`
always refers to a type.
It's confusing to read code where `str` (or another standard type name)
is used as an identifier. It also produces misleading syntax
highlighting.
stabilize const_swap
libs-api FCP passed in https://github.com/rust-lang/rust/issues/83163.
However, I only just realized that this actually involves an intrinsic. The intrinsic could be implemented entirely with existing stable const functionality, but we choose to make it a primitive to be able to detect more UB. So nominating for `@rust-lang/lang` to make sure they are aware; I leave it up to them whether they want to FCP this.
While at it I also renamed the intrinsic to make the "nonoverlapping" constraint more clear.
Fixes#83163
ptr::copy: fix docs for the overlapping case
Fixes https://github.com/rust-lang/unsafe-code-guidelines/issues/549
As discussed in that issue, it doesn't make any sense for `copy` to read a byte via `src` after it was already written via `dst`. The entire point of this method is that is copies correctly even if they overlap, and that requires always reading any given location before writing it.
Cc `@rust-lang/opsem`
Begin to implement type system layer of unsafe binders
Mostly TODOs, but there's a lot of match arms that are basically just noops so I wanted to split these out before I put up the MIR lowering/projection part of this logic.
r? oli-obk
Tracking:
- https://github.com/rust-lang/rust/issues/130516
Variants::Single: do not use invalid VariantIdx for uninhabited enums
~~Stacked on top of https://github.com/rust-lang/rust/pull/133681, only the last commit is new.~~
Currently, `Variants::Single` for an empty enum contains a `VariantIdx` of 0; looking that up in the enum variant list will ICE. That's quite confusing. So let's fix that by adding a new `Variants::Empty` case for types that have 0 variants.
try-job: i686-msvc
Use field init shorthand where possible
Field init shorthand allows writing initializers like `tcx: tcx` as
`tcx`. The compiler already uses it extensively. Fix the last few places
where it isn't yet used.
EDIT: this PR also updates `rustfmt.toml` to set
`use_field_init_shorthand = true`.
`rustc_span::symbol` defines some things that are re-exported from
`rustc_span`, such as `Symbol` and `sym`. But it doesn't re-export some
closely related things such as `Ident` and `kw`. So you can do `use
rustc_span::{Symbol, sym}` but you have to do `use
rustc_span::symbol::{Ident, kw}`, which is inconsistent for no good
reason.
This commit re-exports `Ident`, `kw`, and `MacroRulesNormalizedIdent`,
and changes many `rustc_span::symbol::` qualifiers in `compiler/` to
`rustc_span::`. This is a 200+ net line of code reduction, mostly
because many files with two `use rustc_span` items can be reduced to
one.
Field init shorthand allows writing initializers like `tcx: tcx` as
`tcx`. The compiler already uses it extensively. Fix the last few places
where it isn't yet used.
Bounds-check with PtrMetadata instead of Len in MIR
Rather than emitting `Len(*_n)` in array index bounds checks, emit `PtrMetadata(copy _n)` instead -- with some asterisks for arrays and `&mut` that need it to be done slightly differently.
We're getting pretty close to removing `Len` entirely, actually. I think just one more PR after this (for slice drop shims).
r? mir
Make some types and methods related to Polonius + Miri public
We have a tool, [Aquascope](https://github.com/cognitive-engineering-lab/aquascope/), which uses Polonius and Miri to visualize the compile-time and run-time semantics of a Rust program. Changes in the last few months to both APIs have hidden away details we depend upon. This PR re-exposes some of those details, specifically:
**Polonius:**
- `BorrowSet` and `BorrowData` are added to `rustc_borrowck::consumers`, and their fields are made `pub` instead of `pub(crate)`. We need this to interpret the `BorrowIndex`es generated by Polonius.
- `BorrowSet::build` is now `pub`. We need this because the borrowck API doesn't provide access to the `BorrowSet` constructed during checking.
- `PoloniusRegionVid` is added to `rustc_borrowck::consumers`. We need this because it's also contained in the Polonius facts.
**Miri:**
- `InterpCx::local_to_op` is now a special case of `local_at_frame_to_op`, which allows querying locals in any frame. We need this because we walk the whole stack at each step to collect the state of memory.
- `InterpCx::layout_of_local` is now `pub`. We need this because we need to know the layout of every local at each step.
If these changes go against some design goal for keeping certain types private, please let me know so we can hash out a better solution. Additionally, if there's a better way to document that it's important that certain types stay public, also let me know. For example, `BorrowSet` was previously public but was hidden in 6676cec, breaking our build.
cc ```@RalfJung``` ```@nnethercote``` ```@gavinleroy```
fix ICE on type error in promoted
Fixes https://github.com/rust-lang/rust/issues/133968
Ensure that when we turn a type error into a "this promoted failed to evaluate" error, we do record this as something that may happen even in "infallible" promoteds.
Extend Miri to correctly pass mutable pointers through FFI
Based off of https://github.com/rust-lang/rust/pull/129684, this PR further extends Miri to execute native calls that make use of pointers to *mutable* memory.
We adapt Miri's bookkeeping of internal state upon any FFI call that gives external code permission to mutate memory.
Native code may now possibly write and therefore initialize and change the pointer provenance of bytes it has access to: Such memory is assumed to be *initialized* afterwards and bytes are given *arbitrary (wildcard) provenance*. This enables programs that correctly use mutating FFI calls to run Miri without errors, at the cost of possibly missing Undefined Behaviour caused by incorrect usage of mutating FFI.
> <details>
>
> <summary> Simple example </summary>
>
> ```rust
> extern "C" {
> fn init_int(ptr: *mut i32);
> }
>
> fn main() {
> let mut x = std::mem::MaybeUninit::<i32>::uninit();
> let x = unsafe {
> init_int(x.as_mut_ptr());
> x.assume_init()
> };
>
> println!("C initialized my memory to: {x}");
> }
> ```
> ```c
> void init_int(int *ptr) {
> *ptr = 42;
> }
> ```
> should now show `C initialized my memory to: 42`.
>
> </details>
r? ``@RalfJung``
