Add `unwrap_or_default` method to `Result`

Fixes #37025

Implement `RefUnwindSafe` for atomic types

Closes #37136

hashmap: Store hashes as usize internally

We can't use more than usize's bits of a hash to select a bucket anyway,
so we only need to store that part in the table. This should be an
improvement for the size of the data structure on 32-bit platforms.
Smaller data means better cache utilization and hopefully better
performance.

Fixes #36567

Make all vec! macros use square brackets: Attempt 2

[The last PR](https://github.com/rust-lang/rust/pull/37476) ended with tears after a valiant struggle with git. I managed to clean up the completely broken history of that into a brand spanking new PR! Yay!

Original:

> Everyone hates the old syntax. I hope. Otherwise this PR has some controversy I wasn't expecting.

> This would be the perfect time to write a lint recommending vec![..] when you use another style.

> Disclaimer: I may have broken something. If I have, I'll fix them when the tests come in. Luckily the chance for a non-syntactical error is pretty low in all this.

Most of the Rust community agrees that the vec! macro is clearer when
called using square brackets [] instead of regular brackets (). Most of
these ocurrences are from before macros allowed using different types of
brackets.

There is one left unchanged in a pretty-print test, as the pretty
printer still wants it to have regular brackets.

introing one-time diagnostics: only emit "lint level defined here" once

This is a revised resubmission of PR #34084 (which was closed due to inactivity on account of time constraints on the author's part).
---

We introduce a new `one_time_diagnostics` field on
`rustc::session::Session` to hold a hashset of diagnostic messages we've
set once but don't want to see again (as uniquified by span and message
text), "lint level defined here" being the motivating example dealt with
here.

This is in the matter of #24690.
---

r? @nikomatsakis

Rollup of 5 pull requests

- Successful merges: #37438, #37458, #37462, #37475, #37486
- Failed merges:

Fix typo in the BitAndAssign operator documentation

The name of the operator should be `&=` instead of `&`.

Add E0532 error explanation

This resolves one of the error list in https://github.com/rust-lang/rust/issues/35347 - just because I stumbled over it today.

I assumed the error code should be removed from `register_diagnostics!` because it's now defined above.

Since that is my first code contribution, please check that all is in order. It would be helpful to know how to run the test for the `compile_fail,E0532` part. I did `make check-stage1-cfail NO_REBUILD=1` but that doesn't test the inlined example.

r? @GuillaumeGomez

Remove outdated fixme comment.

Linked issue has been closed, but the comment was not removed.

If this is still an issue, then the comment should probably be updated.

r? @petrochenkov

Fix more spans in deriving::generic

r? @petrochenkov

improve docs for Index and IndexMut

This mainly changes the boring example of Foo/Bar of `IndexMut` into a better one.

Also added explanations about syntactic sugar for `v[index]`.

Closes #36329

LLVM: Update submodule to rust-llvm-2016-10-29 branch.

Fixes #37227

Replace all uses of SHA-256 with BLAKE2b.

Removes the SHA-256 implementation and replaces all uses of it with BLAKE2b, which we already use for debuginfo type guids and incremental compilation hashes. It doesn't make much sense to have two different cryptographic hash implementations in the compiler and Blake has a few advantages over SHA-2 (computationally less expensive, hashes of up to 512 bits).

Do not clone Mir unnecessarily

r? @EddyB

save-analysis: change imports to carry a ref id rather than their own…

… node id

To make jump to def for imports work

r? @EddyB

Fix ICE when attempting to print closure generics

Fixes #36622.

r? @EddyB or @arielb1

Shrink Expr_::ExprInlineAsm.

On 64-bit this reduces the size of `Expr_` from 144 to 64 bytes, and
reduces the size of `Expr` from 176 to 96 bytes.

For the workload in #36799 this reduces the RSS for the "lowering ast -> hir" phase and all subsequent phases by 50 MiB, which reduces the peak RSS for that workload by about 1%. Not huge, but it's a very easy improvement.

r? @EddyB

Move `CrateConfig` from `Crate` to `ParseSess`

This is a syntax-[breaking-change]. Most breakage can be fixed by removing a `CrateConfig` argument.
r? @EddyB

Disable jemalloc on aarch64/powerpc

Sounds like jemalloc is broken on systems which differ in page size than the
host it was compiled on (unless an option was passed). This unfortunately
reduces the portability of binaries created and can often make Rust segfault by
default. For now let's patch over this by disabling jemalloc until we can figure
out a better solution.

Closes #36994
Closes #37320
cc jemalloc/jemalloc#467

[2/n] rustc_metadata: move is_extern_item to trans.

*This is part of a series ([prev](https://github.com/rust-lang/rust/pull/37400) | [next](https://github.com/rust-lang/rust/pull/37402)) of patches designed to rework rustc into an out-of-order on-demand pipeline model for both better feature support (e.g. [MIR-based](https://github.com/solson/miri) early constant evaluation) and incremental execution of compiler passes (e.g. type-checking), with beneficial consequences to IDE support as well.
If any motivation is unclear, please ask for additional PR description clarifications or code comments.*
<hr>

Minor cleanup missed by #36551: `is_extern_item` is one of, if not the only `CrateStore` method who takes a `TyCtxt` but doesn't produce something cached in it, and such methods are going away.

[1/n] Move the MIR map into the type context.

*This is part of a series ([prev]() | [next](https://github.com/rust-lang/rust/pull/37401)) of patches designed to rework rustc into an out-of-order on-demand pipeline model for both better feature support (e.g. [MIR-based](https://github.com/solson/miri) early constant evaluation) and incremental execution of compiler passes (e.g. type-checking), with beneficial consequences to IDE support as well.
If any motivation is unclear, please ask for additional PR description clarifications or code comments.*
<hr>

The first commit reorganizes the `rustc::mir` module to contain the MIR types directly without an extraneous `repr` module which serves no practical purpose but is rather an eyesore.

The second commit performs the actual move of the MIR map into the type context, for the purposes of future integration with requesting analysis/lowering by-products through `TyCtxt`.

Local `Mir` bodies need to be mutated by passes (hence `RefCell`), and at least one pass (`qualify_consts`) needs simultaneous access to multiple `Mir` bodies (hence arena-allocation).
`Mir` bodies loaded from other crates appear as if immutably borrowed (by `.borrow()`-ing one `Ref` and subsequently "leaking" it) to avoid, at least dynamically, *any* possibility of their local mutation.

One caveat is that lint passes can now snoop at the MIR (helpful) or even mutate it (dangerous).
However, lints are unstable anyway and we can find a way to deal with this in due time.
Future work will result in a tighter API, potentially hiding mutation *completely* outside of MIR passes.

Print out the error when HeapFree failures do occur

cc https://github.com/rust-lang/rust/issues/37395

I'd prefer to use `assert!` instead of `debug_assert!` if the cost is acceptable.

r? @alexcrichton

rustc_typeck: Allow reification from fn item to unsafe ptr

See https://github.com/rust-lang/rfcs/issues/1762.

I've never contributed to the compiler internals before-- apologies if I'm not going about this the right way.

Do not intern filemap to entry w/ mismatched length.

Do not intern filemap to entry w/ mismatched length.

Fix #37274 (I think).

Beta-nominated; note that only the second commit needs to be cherry picked to beta branch. (The first just adds some debug instrumentation that I wish had been present.)

Prohibit patterns in trait methods without bodies

They are not properly type checked
```rust
trait Tr {
    fn f(&a: u8); // <- This compiles
}
```
, mostly rejected by the parser already and generally don't make much sense.
This PR is kind of a missing part of https://github.com/rust-lang/rust/pull/35015.

Given the [statistics from crater](https://github.com/rust-lang/rust/pull/37378#issuecomment-256154994), the effect of this PR is mostly equivalent to improving `unused_mut` lint.

cc https://github.com/rust-lang/rust/issues/35078#issuecomment-255707355 https://github.com/rust-lang/rust/pull/35015 https://github.com/rust-lang/rfcs/pull/1685 https://github.com/rust-lang/rust/issues/35203
r? @EddyB

Support for aarch64 architecture on Fuchsia

This patch adds support for the aarch64-unknown-fuchsia target. Also
updates src/liblibc submodule to include required libc change.

Add support for kernel randomness for Fuchsia

Wire up cprng syscall as provider for rand::os::OsRng on Fuchsia.

Avoid more allocations when compiling html5ever

These three commits reduce the number of allocations performed when compiling html5ever from 13.2M to 10.8M, which speeds up compilation by about 2%.

r? @nrc