During coverage instrumentation, this variable always holds the coverage graph,
which is a simplified view of the MIR control-flow graph. The new name is
clearer in context, and also shorter.
Rename `elem_offset` to `element_offset`
Tracking issue: #126769
Renames `slice::elem_offset` to `slice::element_offset` and improves the documentation of it and its related methods.
The current documentation can be misinterpreted (as explained [here](https://github.com/rust-lang/rust/issues/126769#issuecomment-2453363897)).
docs: Mention `spare_capacity_mut()` in `Vec::set_len`
I recently went down a small rabbit hole when trying to identify safe use of `Vec::set_len`. The solution was `Vec::spare_capacity_mut`. I think the docs on `Vec::set_len` benefit from mentioning this method.
A possible counter-argument could be that the [clippy lint `uninit_vec`](https://rust-lang.github.io/rust-clippy/master/index.html#/uninit_vec) already nudges people in the right direction. However, I think a working example on `Vec::set_len` is still beneficial.
Happy to hear your thoughts on the matter. 😊
Use `MixedBitSet`s in const qualif
These analyses' domains should be very homogeneous, having compressed bitmaps on huge cfgs should make a difference (and doesn’t have an impact on the smaller / regular cfgs in our benchmarks).
This is a >40% walltime reduction on [this stress test](https://github.com/Manishearth/icu4x_compile_sample) extracted from a real world ICU case, and a 10x or so max-rss reduction.
cc `@oli-obk` `@RalfJung`
Should help with (or fix) issue #134404.
Speed up `Parser::expected_tokens`
The constant pushing/clearing of `Parser::expected_tokens` during parsing is slow. This PR speeds it up greatly.
r? `@estebank`
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
Remove a duplicated check that doesn't do anything anymore.
fixes#134005
This code didn't actually `lub` the type of the previous expressions, but just the current type over and over again. Changing it to using the actual expression type does not change anything either, so may as well remove the entire loop.
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)
