We already did `Transmute`-then-`PtrToPtr`; this adds the nearly-identical `PtrToPtr`-then-`Transmute`.
It also adds `transmute(Foo(x))` → `transmute(x)`, when `Foo` is a single-field transparent type. That's useful for things like `NonNull { pointer: p }.as_ptr()`.
Found these as I was looking at MCP807-related changes.
Use `PtrMetadata` instead of `Len` in slice drop shims
I tried to do a bigger change in #134297 which didn't work, so here's the part I really wanted: Removing another use of `Len`, in favour of `PtrMetadata`.
Split into two commits where the first just adds a test, so you can look at the second commit to see how the drop shim for an array changes with this PR.
Reusing the same reviewer from the last one:
r? BoxyUwU
Make sure we handle `backwards_incompatible_lint` drops appropriately in drop elaboration
In #131326, a new kind of scheduled drop (`drop_kind: DropKind::Value` + `backwards_incompatible_lint: true`) was added so that we could insert a new kind of no-op MIR statement (`backward incompatible drop`) for linting purposes.
These drops were intended to have *no side-effects*, but drop elaboration code forgot to handle these drops specially and they were handled otherwise as normal drops in most of the code. This ends up being **unsound** since we insert more than one drop call for some values, which means that `Drop::drop` could be called more than once.
This PR fixes this by splitting out the `DropKind::ForLint` and adjusting the code. I'm not totally certain if all of the places I've adjusted are either reachable or correct, but I'm pretty certain that it's *more* correct than it was previously.
cc `@dingxiangfei2009`
r? nikomatsakis
Fixes#134482
coverage: Store coverage source regions as `Span` until codegen (take 2)
This is an attempt to re-land #133418:
> Historically, coverage spans were converted into line/column coordinates during the MIR instrumentation pass.
> This PR moves that conversion step into codegen, so that coverage spans spend most of their time stored as Span instead.
> In addition to being conceptually nicer, this also reduces the size of coverage mappings in MIR, because Span is smaller than 4x u32.
That PR was reverted by #133608, because in some circumstances not covered by our test suite we were emitting coverage metadata that was causing `llvm-cov` to exit with an error (#133606).
---
The implementation here is *mostly* the same, but adapted for subsequent changes in the relevant code (e.g. #134163).
I believe that the changes in #134163 should be sufficient to prevent the problem that required the original PR to be reverted. But I haven't been able to reproduce the original breakage in a regression test, and the `llvm-cov` error message is extremely unhelpful, so I can't completely rule out the possibility of this breaking again.
r? jieyouxu (reviewer of the original PR)
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
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
We don't need `NonNull::as_ptr` debuginfo
In order to stop pessimizing the use of local variables in core, skip debug info for MIR temporaries in tiny (single-BB) functions.
For functions as simple as this -- `Pin::new`, etc -- nobody every actually wants debuginfo for them in the first place. They're more like intrinsics than real functions, and stepping over them is good.
Stop pessimizing the use of local variables in core by skipping debug info for MIR temporaries in tiny (single-BB) functions.
For functions as simple as this -- `Pin::new`, etc -- nobody every actually wants debuginfo for them in the first place. They're more like intrinsics than real functions, and stepping over them is good.
Implementation of `fmt::FormattingOptions`
Tracking issue: #118117
Public API:
```rust
#[derive(Copy, Clone, Debug, PartialEq, Eq)]
pub struct FormattingOptions { … }
#[derive(Copy, Clone, Debug, PartialEq, Eq)]
pub enum Sign {
Plus,
Minus
}
#[derive(Copy, Clone, Debug, PartialEq, Eq)]
pub enum DebugAsHex {
Lower,
Upper
}
impl FormattingOptions {
pub fn new() -> Self;
pub fn sign(&mut self, sign: Option<Sign>) -> &mut Self;
pub fn sign_aware_zero_pad(&mut self, sign_aware_zero_pad: bool) -> &mut Self;
pub fn alternate(&mut self, alternate: bool) -> &mut Self;
pub fn fill(&mut self, fill: char) -> &mut Self;
pub fn align(&mut self, alignment: Option<Alignment>) -> &mut Self;
pub fn width(&mut self, width: Option<usize>) -> &mut Self;
pub fn precision(&mut self, precision: Option<usize>) -> &mut Self;
pub fn debug_as_hex(&mut self, debug_as_hex: Option<DebugAsHex>) -> &mut Self;
pub fn get_sign(&self) -> Option<Sign>;
pub fn get_sign_aware_zero_pad(&self) -> bool;
pub fn get_alternate(&self) -> bool;
pub fn get_fill(&self) -> char;
pub fn get_align(&self) -> Option<Alignment>;
pub fn get_width(&self) -> Option<usize>;
pub fn get_precision(&self) -> Option<usize>;
pub fn get_debug_as_hex(&self) -> Option<DebugAsHex>;
pub fn create_formatter<'a>(self, write: &'a mut (dyn Write + 'a)) -> Formatter<'a>;
}
impl<'a> Formatter<'a> {
pub fn new(write: &'a mut (dyn Write + 'a), options: FormattingOptions) -> Self;
pub fn with_options<'b>(&'b mut self, options: FormattingOptions) -> Formatter<'b>;
pub fn sign(&self) -> Option<Sign>;
pub fn options(&self) -> FormattingOptions;
}
```
Relevant changes from the public API in the tracking issue (I'm leaving out some stuff I consider obvious mistakes, like missing `#[derive(..)]`s and `pub` specifiers):
- `enum DebugAsHex`/`FormattingOptions::debug_as_hex`/`FormattingOptions::get_debug_as_hex`: To support `{:x?}` as well as `{:X?}`. I had completely missed these options in the ACP. I'm open for any and all bikeshedding, not married to the name.
- `fill`/`get_fill` now takes/returns `char` instead of `Option<char>`. This simply mirrors what `Formatter::fill` returns (with default being `' '`).
- Changed `zero_pad`/`get_zero_pad` to `sign_aware_zero_pad`/`get_sign_aware_zero_pad`. This also mirrors `Formatter::sign_aware_zero_pad`. While I'm not a fan of this quite verbose name, I do believe that having the interface of `Formatter` and `FormattingOptions` be compatible is more important.
- For the same reason, renamed `alignment`/`get_alignment` to `aling`/`get_align`.
- Deviating from my initial idea, `Formatter::with_options` returns a `Formatter` which has the lifetime of the `self` reference as its generic lifetime parameter (in the original API spec, the generic lifetime of the returned `Formatter` was the generic lifetime used by `self` instead). Otherwise, one could construct two `Formatter`s that both mutably borrow the same underlying buffer, which would be unsound. This solution still has performance benefits over simply using `Formatter::new`, so I believe it is worthwhile to keep this method.
coverage: Use a separate counter type and simplification step during counter creation
When instrumenting a function's MIR for coverage, there is a point where we need to decide, for each node in the control-flow graph, whether its execution count will be tracked by a physical counter, or by an expression that combines physical counters from other parts of the graph.
Currently the code for doing that is heavily tied to the final form of the LLVM coverage mapping format, and performs some important simplification steps on-the-fly. These factors make the code extremely difficult to modify without breaking or massively worsening the resulting coverage-instrumentation metadata.
---
This PR aims to improve that situation somewhat by adding an extra intermediate representation between the code that chooses how each node will be counted, and the code that converts those decisions into actual tables of physical counters and trees of counter expressions.
As part of doing that, some of the simplifications that are currently performed during the main counter creation step have been pulled out into a separate step.
In most cases the resulting coverage metadata is equivalent, slightly better, or slightly worse. The biggest outlier is `counters.rs`, where the coverage metadata ends up about 10% larger. This seems to be the result of the new approach having less subexpression sharing (because it relies on flatten-sort-cancel), and therefore being less effective at taking advantage of MIR optimizations to replace counters for unused control-flow with zeroes. I think the modest downside is acceptable in light of the future possibilities opened up by this decoupling.
Update `NonZero` and `NonNull` to not field-project (per MCP#807)
https://github.com/rust-lang/compiler-team/issues/807#issuecomment-2506098540 was accepted, so this is the first PR towards moving the library to not using field projections into `[rustc_layout_scalar_valid_range_*]` types.
`NonZero` was already using `transmute` nearly everywhere, so there are very few changes to it.
`NonNull` needed more changes, but they're mostly simple, changing `.pointer` to `.as_ptr()`.
r? libs
cc #133324, which will tidy up some of the MIR from this a bit more, but isn't a blocker.
coverage: Store coverage source regions as `Span` until codegen
Historically, coverage spans were converted into line/column coordinates during the MIR instrumentation pass.
This PR moves that conversion step into codegen, so that coverage spans spend most of their time stored as `Span` instead.
In addition to being conceptually nicer, this also reduces the size of coverage mappings in MIR, because `Span` is smaller than 4x u32.
---
There should be no changes to coverage output.
