We're not quite ready to ship parallel compilers by default, but the alt
builders are not used too much (in theory), so we believe that shipping
a possibly-broken compiler there is not too problematic.

…ible.

… new API.

This changes the default parallelism for parallel compilers to one,
instead of the previous default, which was "num cpus". This is likely
not an optimal default long-term, but it is a good default for testing
whether parallel compilers are not a significant regression over a
sequential compiler.

Notably, this in theory makes a parallel-enabled compiler behave
exactly like a sequential compiler with respect to the jobserver.

apfloat: improve doc comments

r? @eddyb @nagisa

…xcrichton

Make all alt builders produce parallel-enabled compilers

We're not quite ready to ship parallel compilers by default, but the alt
builders are not used too much (in theory), so we believe that shipping
a possibly-broken compiler there is not too problematic.

r? @nikomatsakis

BTreeSet intersection, is_subset & difference optimizations

...based on the range of values contained; in particular, a massive improvement when these ranges are disjoint (or merely touching), like in the neg-vs-pos benchmarks already in liballoc. Inspired by rust-lang#64383 but none of the ideas there worked out.

I introduced another variant in IntersectionInner and in DifferenceInner, because I couldn't find a way to initialize these iterators as empty if there's no empty set around.

Also, reduced the size of "large" sets in test cases - if Miri can't handle it, it was needlessly slowing down everyone.

…i-refactor, r=wesleywiser

SelfProfiler API refactoring and part one of event review

This PR refactors the `SelfProfiler` a little bit so that most profiling methods are RAII-based. The codegen backend code already had something similar, this refactoring pulls this functionality up into `SelfProfiler` itself, for general use.

The second commit of this PR is a review and update of the existing events we are already recording. Names have been made more consistent. CGU names have been removed from event names. They will be added back in when function parameter recording is implemented.

There is still some work to be done for adding new events, especially around trait resolution and the incremental system.

r? @wesleywiser

syntax: cleanup param, method, and misc parsing

Do some misc cleanup of the parser:
- Method and parameter parsing is refactored.
- A parser for `const | mut` is introduced that rust-lang#64588 can reuse.
- Some other misc parsing.

Next up in a different PR:
- ~Implementing rust-lang#64252 -- maybe some other time...
- Heavily restructuring up `item.rs` which is a mess (hopefully, no promises ^^).

r? @petrochenkov

…chievink

Remove unneeded `fn main` blocks from docs

## [No whitespace diff](https://github.com/rust-lang/rust/pull/64912/files?w=1)

Fixes rust-lang#64919. Suggest fix based on operator precendence.

Fixes rust-lang#64919

…excrichton

Update cargo.

Pulls rust-lang/cargo@f3c92ed into nightly Rust.

r? @alexcrichton