std: Start implementing wasm32 atomics
This commit is an initial start at implementing the standard library for
wasm32-unknown-unknown with the experimental `atomics` feature enabled. None of
these changes will be visible to users of the wasm32-unknown-unknown target
because they all require recompiling the standard library. The hope with this is
that we can get this support into the standard library and start iterating on it
in-tree to enable experimentation.
Currently there's a few components in this PR:
* Atomic fences are disabled on wasm as there's no corresponding atomic op and
it's not clear yet what the convention should be, but this will change in the
future!
* Implementations of `Mutex`, `Condvar`, and `RwLock` were all added based on
the atomic intrinsics that wasm has.
* The `ReentrantMutex` and thread-local-storage implementations panic currently
as there's no great way to get a handle on the current thread's "id" yet.
Right now the wasm32 target with atomics is unfortunately pretty unusable,
requiring a lot of manual things here and there to actually get it operational.
This will likely continue to evolve as the story for atomics and wasm unfolds,
but we also need more LLVM support for some operations like custom `global`
directives for this to work best.
adopt "placeholders" to represent universally quantified regions
This does a few preliminary refactorings that lay some groundwork for moving towards universe integration. Two things, primarily:
- Rename from "skolemized" to "placeholder"
- When instantiating `for<'a, 'b, 'c>`, just create one universe for all 3 regions, and distinguish them from one another using the `BoundRegion`.
- This is more accurate, and I think that in general we'll be moving towards a model of separating "binder" (universe, debruijn index) from "index within binder" in a number of places.
- In principle, it feels the current setup of making lots of universes could lead to us doing the wrong thing, but I've actually not been able to come up with an example where this is so.
r? @scalexm
cc @arielb1
[NLL] Improve "borrow later used here" messages
* In the case of two conflicting borrows, the later used message says which borrow it's referring to
* If the later use is a function call (from the users point of view) say that the later use is for the call. Point just to the function.
r? @pnkfelix
Closes#48643
Introduce `TyKind::UnnormalizedProjection`
Introduce a new variant used for lazy normalization in chalk integration. Mostly `bug!` everywhere.
r? @nikomatsakis
A handful of cleanups for rustc/mir
- use the "regular" `into()` instead of `graphviz::IntoCow` in `mod.rs`
- `format!("{}", x)` > `x.to_string()`
- remove one unnecessary `String` allocation
- shorten the logic of one loop
- `assert!(x == y)` > `assert_eq!(x, y)`
- whitespace & formatting fixes
r? @oli-obk
Remove duplicate predicates in `explicit_predicates_of`
I took a more brutal approach than described in #52187. I could have used the `linked_hash_map` crate but this seems overkill, especially as we need a vec storage in the end.
r? @nikomatsakis
abolish ICE when pretty-printing async block
@jnetterf reported an ICE when the unused-parentheses lint triggered around an async block (#54752). In order to compose an autofixable suggestion, the lint invokes the pretty-printer on the unnecessarily-parenthesized expression. (One wonders why the lint doesn't just use `SourceMap::span_to_snippet` instead, to preserve the formatting of the original source?—but to answer that, you'd have to ask the author of 5c9f806d.)
But then the pretty-printer panics when trying to call `<pprust::State as PrintState>::end` when `State.boxes` is empty. Empirically, the problem would seem to be solved if we start some "boxes" beforehand in the `ast::ExprKind::Async` arm of the big match in `print_expr_outer_attr_style`, exactly like we do in the immediately-preceding match arm for `ast::ExprKind::Block`—it would seem pretty ("pretty") reasonable for the pretty-printing of async blocks to work a lot like the pretty-printing of ordinary non-async blocks, right??
Of course, it would be shamefully cargo-culty to commit code on the basis of this kind of mere reasoning-by-analogy (in contrast to understanding the design of the pretty-printer in such detail that the correctness of the patch is comprehended with all the lucid certainty of mathematical proof, rather than being merely surmised by intuition). But maybe we care more about fixing the bug with high probability today, than with certainty in some indefinite hypothetical future? Maybe the effort is worth [a fifth of a shirt](https://hacktoberfest.digitalocean.com/stats/zackmdavis)??
Humbly resolves#54752.
r? @cramertj
Update a FIXME in memory.rs
In #51833, I improved the performance of `copy_undef_mask()`. As such, the old FIXME wasn't appropriate anymore. The main remaining thing left to do is to implement a fast path for non-overlapping copies (per @oli-obk).
r? @oli-obk
