also move "is there a borrow tracker" check out of the loop

…he closure

Fix a misleading comment in `tests/pass/tree_borrows/tree-borrows.rs`

The original comment is somewhat misleading.

Since we don't add a protector for `x` here, `f` should be allowed to deallocate `x`.

…r=RalfJung

Avoid extra copy by using `retain_mut` and moving the deletion into the closure

Fixes the FIXME introduced in rust-lang#3833. Thanks to `@dmitrii-ubskii` for the idea 🙂

fix calling pipe, pipe2, socketpair with a pointer-to-array

Fixes rust-lang/miri#3839

epoll: Add a EINVAL case

In ``epoll_ctl`` documentation, it is mentioned that:
> EINVAL epfd is not an epoll file descriptor, or fd is the same as epfd, or the requested operation op is not supported by this interface.

So I added this EINVAL case for ``epfd == fd`` in ``epoll_ctl``

epoll: handle edge case for epoll_ctl

There is a test case that revealed that our implementation differs from the real system:
 - Set up an epoll watching the FD
- Call epoll_wait
- Set up another epoll watching the same FD
- Call epoll_wait on the first epoll. Nothing should be reported!

This happened because, in ``epoll_ctl``, we used ``check_and_update_readiness``, which is a function that would return notification for all epoll file description that registered a particular file description. But we shouldn't do that because no notification should be returned if there is no I/O activity between two ``epoll_wait`` (every first ``epoll_wait`` that happens after ``epoll_ctl`` is an exception, we should return notification that reflects the readiness of file description).

r? `@oli-obk`

Co-authored-by: Ralf Jung <post@ralfj.de>

Automatic Rustup

See rust-lang#3846 for more information.

provenance_gc: fix comment

Fixes rust-lang/miri#3826

r? `@saethlin`

tree_borrows test: ensure we can actually read the variable

Disable tree traversal optimization that is wrong due to lazy nodes.

See rust-lang#3846 for more information.

For now, the optimization is disabled in a very "hotfix" way, while we think about potential fixes. Nonetheless, this fixes rust-lang#3846

In preparation for rust-lang#3837, the tree traversal needs to be made bottom-up,
because the current top-down tree traversal, coupled with that PR's
changes to the garbage collector, can introduce non-deterministic error
messages if the GC removes a parent tag of the accessed tag that would
have triggered the error first.

This is a breaking change for the diagnostics emitted by TB. The
implemented semantics stay the same.

… r=RalfJung

Make TB tree traversal bottom-up

In preparation for rust-lang#3837, the tree traversal needs to be made bottom-up, because the current top-down tree traversal, coupled with that PR's changes to the garbage collector, can introduce non-deterministic error messages if the GC removes a parent tag of the accessed tag that would have triggered the error first.

This is a breaking change for the diagnostics emitted by TB. The implemented semantics stay the same.

Follow-up on rust-lang#3833 and rust-lang#3835. In these PRs, the TB GC was fixed to no
longer cause a stack overflow. One test that motivated it was the test
`fill::horizontal_line` in `tiny_skia`. But not causing stack overflows
was not a large improvents, since it did not fix the fundamental issue:
The tree was too large. The test now ran, but it required gigabytes of
memory and hours of time, whereas it finishes within seconds in Stacked
Borrows.

The problem in that test was that it used [`slice::chunked`](https://doc.rust-lang.org/std/primitive.slice.html#method.chunks) to iterate
a slice in chunks. That iterator is written to reborrow at each call to
`next`, which creates a linear tree with a bunch of intermediary nodes,
which also fragments the `RangeMap` for that allocation.

The solution is to now compact the tree, so that these interior nodes
are removed. Care is taken to not remove nodes that are protected, or
that otherwise restrict their children.

Support blocking for epoll

This PR enabled epoll to have blocking operation.

The changes introduced by this PR are:
- Refactored part of the logic in ``epoll_wait`` to ``blocking_epoll_callback``
- Added a new field ``thread_ids`` in ``Epoll`` for blocked thread ids
- Added a new ``BlockReason::Epoll``

Automatic Rustup

Add tokio io test

After rust-lang#3804 landed, these tests passed.

…e-gc, r=RalfJung

Make Tree Borrows Provenance GC compact the tree

Follow-up on rust-lang#3833 and rust-lang#3835. In these PRs, the TB GC was fixed to no longer cause a stack overflow. One test that motivated it was the test `fill::horizontal_line` in [`tiny-skia`](https://github.com/RazrFalcon/tiny-skia). But not causing stack overflows was not a large improvents, since it did not fix the fundamental issue: The tree was too large. The test now ran, but it required gigabytes of memory and hours of time (only for it to be OOM-killed 🤬), whereas it finishes within 24 seconds in Stacked Borrows. With this merged, it finishes in about 40 seconds under TB.

The problem in that test was that it used [`slice::chunked`](https://doc.rust-lang.org/std/primitive.slice.html#method.chunks) to iterate a slice in chunks. That iterator is written to reborrow at each call to `next`, which creates a linear tree with a bunch of intermediary nodes, which also fragments the `RangeMap` for that allocation.

The solution is to now compact the tree, so that these interior nodes are removed. Care is taken to not remove nodes that are protected, or that otherwise restrict their children.

I am currently only 99% sure that this is sound, and I do also think that this could compact even more. So `@Vanille-N` please also have a look at whether I got the compacting logic right.

For a more visual comparison, [here is a gist](https://gist.github.com/JoJoDeveloping/ae4a7f7c29335a4c233ef42d2f267b01) of what the tree looks like at one point during that test, with and without compacting.

This new GC requires a different iteration order during accesses (since the current one can make the error messages non-deterministic), so it is rebased on top of rust-lang#3843 and requires that PR to be merged first.

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