…clif-2020-11-27

Complement to rust-lang#78863

This includes bytecodealliance/wasmtime#2403 which enables hotswapping with SimpleJIT

We now lint on code like this:

```rust
fn main() {
    fn foo() {};
    struct Bar {};
}
```

Previously, this caused warnings in Cargo, so it was disabled.

Co-authored-by: Jonas Schievink <jonasschievink@gmail.com>
Co-authored-by: Vadim Petrochenkov <vadim.petrochenkov@gmail.com>

Co-authored-by: Jonas Schievink <jonasschievink@gmail.com>

This can happen in generic code

Directly use raw pointers in `AtomicPtr` store/load

I was unable to find any reason for this limitation in the latest source of LLVM or in the documentation [here](http://llvm.org/docs/Atomics.html#libcalls-atomic).

fixes rust-lang/miri#1574

LICM in Cranelift has been fixed recently

This commit makes minor changes to the cranelift backend so that it can
build given changes in cg_ssa for Split DWARF.

Signed-off-by: David Wood <david@davidtw.co>

…omatsakis

Move binder for dyn to each list item

This essentially changes `ty::Binder<&'tcx List<ExistentialTraitRef>>` to `&'tcx List<ty::Binder<ExistentialTraitRef>>`.

This is a first step in moving the `dyn Trait` representation closer to Chalk, which we've talked about in `@rust-lang/wg-traits.`

r? `@nikomatsakis`

See rust-lang#80040

…ds rather than the unique closure type in E0121

This is a squash of the titular commit along with these minor commits:
- Improve note
- Improve note pt2

This also adds back a comment that was mistakenly removed in
ac9dfc3.

Lazy compilation has the potential to significantly improve the startup
time of a program. While functions have to be codegened when called, it
is expected that a significant amount of all code is only required when
an error occurs or only when the program is used in certain ways.

The basic approach is to first codegen a shim for each function. This
shim calls the `__cg_clif_jit` function of cg_clif with a pointer to the
`Instance` corresponding to the function for which it is a shim.
`__cg_clif_jit` function then codegens this function and uses the hot
code swapping support of SimpleJIT to redirect future calls to the
function to the real version. Finally it calls the newly codegened
function.

Lazy compilation in jit mode

…clif-2020-12-27

…n_backend, r=oli-obk

Move some more code out of CodegenBackend::{codegen_crate,link}

Kind of a follow up to rust-lang#77795

…r=oli-obk

Lint on redundant trailing semicolon after item

We now lint on code like this:

```rust
fn main() {
    fn foo() {};
    struct Bar {};
}
```

Previously, this caused warnings in Cargo, so it was disabled.

…Simulacrum

Update RELEASES.md for 1.49.0

### [Rendered](https://github.com/XAMPPRocky/rust/tree/relnotes-1.49.0/RELEASES.md)

r? `@Mark-Simulacrum`
cc `@rust-lang/release`

…arkor

Suggest fn ptr rather than fn item and suggest to use `Fn` trait bounds rather than the unique closure type in E0121

Previously, using `_` as a return type in a function that returned a function/closure would provide a diagnostic that would cause a papercut. For example:
```rust
fn f() -> i32 { 0 }
fn fn_ptr() -> _ { f }
fn closure() -> _ { || 0 }
```
would result in this diagnostic:
```rust
error[E0121]: the type placeholder `_` is not allowed within types on item signatures
 --> <anon>:2:16
  |
2 | fn fn_ptr() -> _ { f }
  |                ^
  |                |
  |                not allowed in type signatures
  |                help: replace with the correct return type: `fn() -> i32 {f}`

error[E0121]: the type placeholder `_` is not allowed within types on item signatures
 --> <anon>:3:17
  |
3 | fn closure() -> _ { || 0 }
  |                 ^
  |                 |
  |                 not allowed in type signatures
  |                 help: replace with the correct return type: `[closure@<anon>:3:21: 3:25]`

error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0121`.
```
As can be seen, it was suggested to use the function definition return type `fn() -> i32 { f }` which is not valid syntax as a return type. Additionally, closures cause a papercut as unique closure types (notated in this case as `[closure@<anon>:3:21: 3:25]`) are not valid syntax either.

Instead, this PR implements this version of the diagnostic (this example is for the same code featured above):
```rust
error[E0121]: the type placeholder `_` is not allowed within types on item signatures
 --> <anon>:2:16
  |
2 | fn fn_ptr() -> _ { f }
  |                ^
  |                |
  |                not allowed in type signatures
  |                help: replace with the correct return type: `fn() -> i32`

error[E0121]: the type placeholder `_` is not allowed within types on item signatures
 --> <anon>:3:17
  |
3 | fn closure() -> _ { || 0 }
  |                 ^ not allowed in type signatures
  |
  = help: consider using an `Fn`, `FnMut`, or `FnOnce` trait bound
  = note: for more information on `Fn` traits and closure types, see https://doc.rust-lang.org/book/ch13-01-closures.html

error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0121`.
```
As can be seen in this diagnostic, the papercut for returning a function item is fixed by suggesting the usage of a function pointer as the return type. As for closures, it's suggested to use an `Fn`, `FnMut`, or `FnOnce` trait bound (with further reading on closures and `Fn` traits in *The Book* for beginners). I did not implement a suggestion to use `impl Fn() -> i32` syntax as that was out-of-scope for my abilities at the moment, therefore someone in the future may want to implement that. Also, it's possible to use either `impl Trait` syntax, generics, or generics with a `where` clause, and some users may not want to use `impl Trait` syntax for their own reasons.

This PR fixes rust-lang#80179.

Add more comments to trait queries

This also adds back a comment that was mistakenly removed in
ac9dfc3.

use matches!() macro in more places

…k-Simulacrum

BTreeMap: test split_off (and append) more thoroughly

Using DeterministicRng as a poor man's property based testing rig.
r? `@Mark-Simulacrum`

Document rustc_macros on nightly-rustc

Fixes rust-lang#80345.

![image](https://user-images.githubusercontent.com/23638587/103113442-b7ba2d00-4628-11eb-8a4d-c542f2d170e1.png)
![image](https://user-images.githubusercontent.com/23638587/103113448-bc7ee100-4628-11eb-8657-2d72e88de656.png)

r? `@ehuss`

Remove FIXME in rustc_privacy

rust-lang#71104 has been fixed.

r? `@marmeladema` if you have time, otherwise `@petrochenkov`

…jorn3

Sync rustc_codegen_cranelift

The highlight of this sync are two JIT mode improvements. The first is that it is now possible to use JIT mode when using `-Zcodegen-backend` instead of the custom driver using `-Cllvm-args=mode=jit`. The second one is a new JIT mode that lazily compiles functions when they are called the first time: https://github.com/bjorn3/rustc_codegen_cranelift/pull/1120

In addition this includes a few small runtime performance improvements and various fixes for rustc changes that didn't cause compilation to fail.

r? `@ghost`

`@rustbot` label +A-codegen +A-cranelift +T-compiler