- Round to zero, and representable values cast directly.
- `NaN` goes to 0
- Values beyond the limits of the type are saturated to the "nearest value"
(essentially rounding to zero, in some sense) in the integral type, so e.g.
`f32::INFINITY` would go to `{u,i}N::MAX.`
Miri: unleash all feature gates
IMO it is silly to unleash features that do not even have a feature gate yet, but not unleash features that do. The only thing this achieves is making unleashed mode annoying to use as we have to figure out the feature flags to enable (and not always do the error messages say what that flag is).
Given that the point of `-Z unleash-the-miri-inside-of-you` is to debug the Miri internals, I see no good reason for this extra hurdle. I cannot imagine a situation where we'd use that flag, realize the program also requires some feature gate, and then be like "oh I guess if this feature is unstable I will do something else". Instead, we'll always just add that flag to the code as well, so requiring the flag achieves nothing.
r? @oli-obk @ecstatic-morse
Fixes https://github.com/rust-lang/rust/issues/71630
Use existing framework for backward dataflow analyses
This PR adds support for backward analyses to the dataflow framework and adds a new live variable analysis (based on the existing one in `librustc_mir/util/liveness.rs`). By adding these to the framework instead of having a separate API, all newly implemented backward dataflow analyses get cursors/visitors, `rustc_peek` tests, and graphviz visualizations for free. In the near-term, this makes it much easier to implement global dead-store elimination, and I believe that this will enable even more MIR optimizations in the future.
This PR makes many changes to the dataflow API, since some concepts and terminology only make sense in forward dataflow. Below is a list of the important changes.
- ~~`entry_set` -> `fixpoint` (the fixpoint for backward dataflow problems is after the block's terminator)~~
- `seek_{before,after}` -> `seek_{before,after}_primary_effect` (the unprefixed dataflow effect is now referred to as the "primary" effect instead of the "after" effect. The "before" effect remains the same, although I considered changing it to the "antecedent" effect. In both backward and forward dataflow, the "before" effect is applied prior to the "primary" effect. I feel very strongly that this is the correct choice, as it means consumers don't have to switch between `seek_before` and `seek_after` based on the direction of their analysis.
- `seek_after_assume_call_returns` is now gone. Users can use `ResultsCursor::apply_custom_effect` to emulate it.
- `visit_{statement,terminator}_exit` -> `visit_{statement,terminator}_after_primary_effect`
- `visit_{statement,terminator}` -> `visit_{statement,terminator}_before_primary_effect`
Implementing this also required refactoring the dataflow cursor implementation so it could work in both directions. This is a large percentage of the diff, since the cursor code is rather complex. The fact that the cursor is exhaustively tested in both directions should reassure whomever is unlucky enough to review this 🤣.
In order to avoid computing the reverse CFG for forward dataflow analyses, I've added some hacks to the existing `mir::BodyAndCache` interface. I've requested changes to this interface that would let me implement this more efficiently.
r? @eddyb (feel free to reassign)
cc @rust-lang/wg-mir-opt
Rollup of 4 pull requests
Successful merges:
- #71398 (Add `RefCell::take`)
- #71663 (Fix exceeding bitshifts not emitting for assoc. consts (properly this time, I swear!))
- #71726 (Suggest deref when coercing `ty::Ref` to `ty::RawPtr` with arbitrary mutability)
- #71808 (Add long error explanation for E0539)
Failed merges:
r? @ghost
Suggest deref when coercing `ty::Ref` to `ty::RawPtr` with arbitrary mutability
Fixes#71676
1. Implement dereference suggestion when coercing `ty::Ref` to `ty::RawPtr` with arbitrary mutability.
2. Extract the dereference steps into `deref_steps()`, which removes all the `use` and `pub` noise introduced by last PR #71540, and makes the code more readable.
3. Use the `remove_prefix()` closure which makes the prefix removal more readable.
4. Introduce `Applicability` as a return value of `check_ref` to suggest `Applicability::Unspecified` suggestion.
**Special**: I found it is not possible to genereate `Applicability::MachineApplicable` suggestion for situation like this:
```rust
use std::ops::Deref;
use std::ops::DerefMut;
struct Bar(u8);
struct Foo(Bar);
struct Emm(Foo);
impl Deref for Bar{
type Target = u8;
fn deref(&self) -> &Self::Target {
&self.0
}
}
impl Deref for Foo {
type Target = Bar;
fn deref(&self) -> &Self::Target {
&self.0
}
}
impl Deref for Emm {
type Target = Foo;
fn deref(&self) -> &Self::Target {
&self.0
}
}
impl DerefMut for Bar{
fn deref_mut(&mut self) -> &mut Self::Target {
&mut self.0
}
}
impl DerefMut for Foo {
fn deref_mut(&mut self) -> &mut Self::Target {
&mut self.0
}
}
impl DerefMut for Emm {
fn deref_mut(&mut self) -> &mut Self::Target {
&mut self.0
}
}
fn main() {
let a = Emm(Foo(Bar(0)));
let _: *mut u8 = &a; //~ ERROR mismatched types
}
```
We may suggest `&mut ***a` here, but the `a` is not declared as mutable variable. And also when processing HIR, it's not possible to check if `a` is declared as a mutable variable (currently we do borrow checking with MIR). So we cannot ensure that suggestion when coercing immutable reference to mutable pointer is always machine applicable. Therefore I added a `Applicability` return value in `check_ref()`. And move the `immutable reference -> mutable pointer` situation into a sperate test file without `run-rustfix`. (It seems that `run-rustfix` will also adopt `Applicability::Unspecified` suggestion, which is strange)
Fix exceeding bitshifts not emitting for assoc. consts (properly this time, I swear!)
Fixes#69021 and fixes#71353.
As described in https://github.com/rust-lang/rust/issues/71353#issuecomment-617901923, this PR:
- adds a variant of `try_validation!` called `try_validation_pat!` that allows specific failures to be turned into validation failures (but returns the rest, unchanged), and
- allows `InvalidProgram` to be returned out of validation
r? @RalfJung
Add `RefCell::take`
Add `RefCell::take` to match `Cell` and `Option`.
I also changed a couple of calls to `.replace` to `.take`.
Tracking issue is #71395.
This is my first contribution, please tell me if there's anything I could improve, thanks!
typeck: always expose explicit enum discriminant `AnonConst`s' parent in `generics_of`.
This is similar to #70452 but for explicit `enum` discriminant constant expressions.
However, unlike #70452, this PR should have no effect on stable code, as while it alleviates #43408 errors, there is no way to actually compile an `enum` with generic parameters *and* explicit discriminants, without `#![feature(arbitrary_enum_discriminant)]`, as explicit discriminant expression don't count as uses of parameters (if they did, they would count as invariant uses).
<hr/>
There's also 2 other commits here, both related to #70453:
* "ty: use `delay_span_bug` in `ty::AdtDef::eval_explicit_discr`." - hides the ICEs demonstrated on #70453, when there are other errors (which the next commit adds)
* "typeck/wfcheck: require that explicit enum discriminants const-evaluate succesfully." - closes#70453 by picking alternative "2", i.e. erroring when a discriminant doesn't fully const-evaluate from the perspective of the `enum` definition
In the future, it might be possible to allow `enum` discriminants to actually depend on parameters, but that will likely require #68436 + some way to restrict the values so no two variants can end up with overlapping discriminants.
As this PR would close#70453, it shouldn't be merged until a decision is reached there.
r? @nikomatsakis
Decode qualifs for associated const defaults
Fixes#71734.
We encode qualifs for associated constants, but never expected to decode the qualifs for defaulted associated consts. Fix this, and test that associated const defaults have the correct qualifs cross-crate.
r? @tmandry
Implement `confusable_idents` lint.
This collects all identifier symbols into `ParseSession` and examines them within the non-ascii-idents lint.
The skeleton generation part needs to be added to `unicode-security` crate. Will update this PR when the crate is updated.
r? @petrochenkov
EDIT: also included the `concat_idents` part.
Implement RFC 2523, `#[cfg(version(..))]`
Hi! This is my first contribution to rust, I hope I didn't miss anything. I tried to implement this feature so that `#[cfg(version(1.44.0))]` works but the parser was printing an error that I wasn't sure how to fix so I just opted for implementing `#[cfg(version("1.44.0"))]` (note the quotes).
Tracking issue: #64796
The extracted function can be used by the rest of bootstrap to detect if we've
already built an up-to-date LLVM (and so it's safe for us to either request it
or pretend it exists).
