Merge from rustc

src/building/bootstrapping/debugging-bootstrap.md

@@ -121,6 +121,14 @@ For `#[instrument]`, it's recommended to:
 - Explicitly pick an instrumentation name via `name = ".."` to distinguish between e.g. `run` of different steps.
 - Take care to not cause diverging behavior via tracing, e.g. building extra things only when tracing infra is enabled.
 
+### Profiling bootstrap
+
+You can use the `COMMAND` tracing target to trace execution of most commands spawned by bootstrap. If you also use the `BOOTSTRAP_PROFILE=1` environment variable, bootstrap will generate a Chrome JSON trace file, which can be visualized in Chrome's `chrome://tracing` page or on https://ui.perfetto.dev.
+
+```bash
+$ BOOTSTRAP_TRACING=COMMAND=trace BOOTSTRAP_PROFILE=1 ./x build library
+```
+
 ### rust-analyzer integration?
 
 Unfortunately, because bootstrap is a `rust-analyzer.linkedProjects`, you can't ask r-a to check/build bootstrap itself with `tracing` feature enabled to get relevant completions, due to lack of support as described in <https://github.com/rust-lang/rust-analyzer/issues/8521>.

src/mir/index.md

@@ -304,9 +304,9 @@ The most important rule for
 this representation is that every value must be uniquely represented. In other
 words: a specific value must only be representable in one specific way. For example: there is only
 one way to represent an array of two integers as a `ValTree`:
-`ValTree::Branch(&[ValTree::Leaf(first_int), ValTree::Leaf(second_int)])`.
+`Branch([Leaf(first_int), Leaf(second_int)])`.
 Even though theoretically a `[u32; 2]` could be encoded in a `u64` and thus just be a
-`ValTree::Leaf(bits_of_two_u32)`, that is not a legal construction of `ValTree`
+`Leaf(bits_of_two_u32)`, that is not a legal construction of `ValTree`
 (and is very complex to do, so it is unlikely anyone is tempted to do so).
 
 These rules also mean that some values are not representable. There can be no `union`s in type

src/parallel-rustc.md

@@ -46,8 +46,6 @@ are implemented differently depending on whether `parallel-compiler` is true.
 
 | data structure                   | parallel                                            | non-parallel |
 | -------------------------------- | --------------------------------------------------- | ------------ |
-| Weak                             | std::sync::Weak                                     | std::rc::Weak |
-| Atomic{Bool}/{Usize}/{U32}/{U64} | std::sync::atomic::Atomic{Bool}/{Usize}/{U32}/{U64} | (std::cell::Cell<bool/usize/u32/u64>) |
 | OnceCell                         | std::sync::OnceLock                                 | std::cell::OnceCell |
 | Lock\<T> | (parking_lot::Mutex\<T>) | (std::cell::RefCell) |
 | RwLock\<T> | (parking_lot::RwLock\<T>) | (std::cell::RefCell) |
@@ -58,7 +56,6 @@ are implemented differently depending on whether `parallel-compiler` is true.
 | WriteGuard | parking_lot::RwLockWriteGuard | std::cell::RefMut |
 | MappedWriteGuard | parking_lot::MappedRwLockWriteGuard | std::cell::RefMut |
 | LockGuard | parking_lot::MutexGuard | std::cell::RefMut |
-| MappedLockGuard | parking_lot::MappedMutexGuard | std::cell::RefMut |
 
 - These thread-safe data structures are interspersed during compilation which
   can cause lock contention resulting in degraded performance as the number of
@@ -173,12 +170,10 @@ Here are some resources that can be used to learn more:
 - [This list of interior mutability in the compiler by nikomatsakis][imlist]
 
 [`rayon`]: https://crates.io/crates/rayon
-[Arc]: https://doc.rust-lang.org/std/sync/struct.Arc.html
 [imlist]: https://github.com/nikomatsakis/rustc-parallelization/blob/master/interior-mutability-list.md
 [irlo0]: https://internals.rust-lang.org/t/parallelizing-rustc-using-rayon/6606
 [irlo1]: https://internals.rust-lang.org/t/help-test-parallel-rustc/11503
 [monomorphization]: backend/monomorph.md
 [parallel-rustdoc]: https://github.com/rust-lang/rust/issues/82741
-[Rc]: https://doc.rust-lang.org/std/rc/struct.Rc.html
 [rustc-rayon]: https://github.com/rust-lang/rustc-rayon
 [tracking]: https://github.com/rust-lang/rust/issues/48685