Tree Borrows: Make tree root always be initialized
This PR fixes a slight annoyance we discovered while formally proving that certain optimizations are sound with Tree Borrows. In particular... (copied from the commit message):
There should never be an `Active` but not initialized node in the borrow tree. If such a node exists, and if it has a protector, then on a foreign read, it could become disabled. This leads to some problems when formally proving that read moving optimizations are sound.
The root node is the only node for which this can happen, since all other nodes can only become `Active` when actually used. But special-casing the root node here is annoying to reason about, everything becomes much nicer if we can simply say that *all* `Active` nodes must be initialized. This requires making the root node default-initialized.
This is also more intuitive, since the root arguably becomes initialized during the allocation, which can be considered a write.
There should never be an `Active` but not initialized node in the
borrow tree. If such a node exists, and if it has a protector, then
on a foreign read, it could become disabled. This leads to some
problems when formally proving that read-reordering optimizations are
sound.
The root node is the only node for which this can happen, since all
other nodes can only become `Active` when actually used. But special-
casing the root node here is annoying to reason about, everything
becomes much nicer if we can simply say that *all* `Active` nodes
must be initialized. This requires making the root node default-
initialized.
This is also more intuitive, since the root arguably becomes ini-
tialized during the allocation, which can be considered a write.
... even when the existential has the least RegionVid.
universal regions (of root universe) > placeholders > existentials
The previous behavior, that chooses the minimal RegionVid index, naturally prefers universal regions over others
because they always have the least RegionVids, but there was no guranteed ordering between placeholders and existentials.
Rollup of 10 pull requests
Successful merges:
- #122707 (Fix a typo in the alloc::string::String docs)
- #122769 (extend comments for reachability set computation)
- #122892 (fix(bootstrap/dist): use versioned dirs when vendoring)
- #122896 (Update stdarch submodule)
- #122923 (In `pretty_print_type()`, print `async fn` futures' paths instead of spans.)
- #122950 (Add regression tests for #101903)
- #123039 (Update books)
- #123042 (Import the 2021 prelude in the core crate)
- #123044 (`Instance` is `Copy`)
- #123051 (did I mention that tests are super cool? )
r? `@ghost`
`@rustbot` modify labels: rollup
Print a backtrace in const eval if interrupted
Demo:
```rust
#![feature(const_eval_limit)]
#![const_eval_limit = "0"]
const OW: u64 = {
let mut res: u64 = 0;
let mut i = 0;
while i < u64::MAX {
res = res.wrapping_add(i);
i += 1;
}
res
};
fn main() {
println!("{}", OW);
}
```
```
╭ ➜ ben@archlinux:~/rust
╰ ➤ rustc +stage1 spin.rs
^Cerror[E0080]: evaluation of constant value failed
--> spin.rs:8:33
|
8 | res = res.wrapping_add(i);
| ^ Compilation was interrupted
note: erroneous constant used
--> spin.rs:15:20
|
15 | println!("{}", OW);
| ^^
note: erroneous constant used
--> spin.rs:15:20
|
15 | println!("{}", OW);
| ^^
|
= note: this note originates in the macro `$crate::format_args_nl` which comes from the expansion of the macro `println` (in Nightly builds, run with -Z macro-backtrace for more info)
error: aborting due to previous error
For more information about this error, try `rustc --explain E0080`.
```
`Instance` is `Copy`
No reason to take it by value; it was confusing ``@rcvalle`` to see it being mutated when it's also being passed by ref in some places.
Import the 2021 prelude in the core crate
The `core` crate currently imports the v1 prelude
b3df0d7e5e/library/core/src/lib.rs (L285-L287)
This recently caused an issue when updating the `portable-simd` subtree since it was using a trait that was added to the 2021 prelude: https://github.com/rust-lang/rust/pull/122905#discussion_r1536228822
To make it easier to have a consistent build environment for subtrees and submodules that get included in `core`, we will now import the 2021 prelude into `core`.
Fixes#122912
r? `@Nilstrieb`
In `pretty_print_type()`, print `async fn` futures' paths instead of spans.
This makes `-Zprint-type-sizes`'s output easier to read, because the name of an `async fn` is more immediately recognizable than its span. This change will also synergize with my other `-Zprint-type-sizes` PR #122922 which prints the type of child futures being awaited.
I also deleted the comment "FIXME(eddyb) should use `def_span`." because it appears to have already been fixed by commit 67727aa7c3.
fix(bootstrap/dist): use versioned dirs when vendoring
Currently, if you attempt to run ui tests in a vendored build, you will
see this failure
```
---- [ui] tests/ui/issues/issue-21763.rs stdout ----
diff of stderr:
8 = note: required because it appears within the type `(Rc<()>, Rc<()>)`
9 = note: required for `hashbrown::raw::RawTable<(Rc<()>, Rc<()>)>` to implement `Send`
10 note: required because it appears within the type `hashbrown::map::HashMap<Rc<()>, Rc<()>, RandomState>`
- --> $HASHBROWN_SRC_LOCATION
+ --> /rust/deps/hashbrown/src/map.rs:190:12
12 note: required because it appears within the type `HashMap<Rc<()>, Rc<()>>`
13 --> $SRC_DIR/std/src/collections/hash/map.rs:LL:COL
14 note: required by a bound in `foo`
```
This happens because the code that attempts to remap
`HASHBROWN_SRC_LOCATION` expects it to be under `hashbrown-$version`,
which is the case in a normal cargo registry, but not when vendoring, where
by default crates may not have the version in their directory name.
This change passes `--versioned-dirs` to `cargo vendor` to enforce that
every crate includes the version in the subdir name, which fixes the ui
test and brings `--enable-vendor` builds closer to normal ones.
