Upgrade to LLVM's master branch (LLVM 7)
### Current status
~~Blocked on a [performance regression](https://github.com/rust-lang/rust/pull/51966#issuecomment-402320576). The performance regression has an [upstream LLVM issue](https://bugs.llvm.org/show_bug.cgi?id=38047) and has also [been bisected](https://reviews.llvm.org/D44282) to an LLVM revision.~~
Ready to merge!
---
This commit upgrades the main LLVM submodule to LLVM's current master branch.
The LLD submodule is updated in tandem as well as compiler-builtins.
Along the way support was also added for LLVM 7's new features. This primarily
includes the support for custom section concatenation natively in LLD so we now
add wasm custom sections in LLVM IR rather than having custom support in rustc
itself for doing so.
Some other miscellaneous changes are:
* We now pass `--gc-sections` to `wasm-ld`
* The optimization level is now passed to `wasm-ld`
* A `--stack-first` option is passed to LLD to have stack overflow always cause
a trap instead of corrupting static data
* The wasm target for LLVM switched to `wasm32-unknown-unknown`.
* The syntax for aligned pointers has changed in LLVM IR and tests are updated
to reflect this.
* ~~The `thumbv6m-none-eabi` target is disabled due to an [LLVM bug][llbug]~~
Nowadays we've been mostly only upgrading whenever there's a major release of
LLVM but enough changes have been happening on the wasm target that there's been
growing motivation for quite some time now to upgrade out version of LLD. To
upgrade LLD, however, we need to upgrade LLVM to avoid needing to build yet
another version of LLVM on the builders.
The revision of LLVM in use here is arbitrarily chosen. We will likely need to
continue to update it over time if and when we discover bugs. Once LLVM 7 is
fully released we can switch to that channel as well.
[llbug]: https://bugs.llvm.org/show_bug.cgi?id=37382
cc #50543
This commit upgrades the main LLVM submodule to LLVM's current master branch.
The LLD submodule is updated in tandem as well as compiler-builtins.
Along the way support was also added for LLVM 7's new features. This primarily
includes the support for custom section concatenation natively in LLD so we now
add wasm custom sections in LLVM IR rather than having custom support in rustc
itself for doing so.
Some other miscellaneous changes are:
* We now pass `--gc-sections` to `wasm-ld`
* The optimization level is now passed to `wasm-ld`
* A `--stack-first` option is passed to LLD to have stack overflow always cause
a trap instead of corrupting static data
* The wasm target for LLVM switched to `wasm32-unknown-unknown`.
* The syntax for aligned pointers has changed in LLVM IR and tests are updated
to reflect this.
* The `thumbv6m-none-eabi` target is disabled due to an [LLVM bug][llbug]
Nowadays we've been mostly only upgrading whenever there's a major release of
LLVM but enough changes have been happening on the wasm target that there's been
growing motivation for quite some time now to upgrade out version of LLD. To
upgrade LLD, however, we need to upgrade LLVM to avoid needing to build yet
another version of LLVM on the builders.
The revision of LLVM in use here is arbitrarily chosen. We will likely need to
continue to update it over time if and when we discover bugs. Once LLVM 7 is
fully released we can switch to that channel as well.
[llbug]: https://bugs.llvm.org/show_bug.cgi?id=37382
rustdoc: Hide struct and enum variant constructor imports
This is fallout from #51425. The duplicate variant imports can be seen [here](https://doc.rust-lang.org/nightly/std/prelude/v1/index.html) for example.
This is fixing a regression so could be backported to beta.
r? @QuietMisdreavus
Rollup of 14 pull requests
Successful merges:
- #51619 (rust: add initial changes to support powerpc64le musl)
- #51793 (Fix variant background color on hover in search results)
- #52005 (Update LLVM to bring in a wasm codegen fix)
- #52016 (Deduplicate error reports for statics)
- #52019 ([cross-lang-lto] Allow the linker to choose the LTO-plugin (which is useful when using LLD))
- #52030 (Any docs preposition change)
- #52031 (Strenghten synchronization in `Arc::is_unique`)
- #52033 ([Gardening] Update outdated comments: ByVal -> Scalar)
- #52055 (Include VS 2017 in error message.)
- #52063 (Add a link to the rustc docs)
- #52073 (Add a punch card to weird expressions test)
- #52080 (Improve dependency deduplication diagnostics)
- #52093 (rustc: Update tracking issue for wasm_import_module)
- #52096 (Fix typo in cell.rs)
Failed merges:
rustdoc codeblock hash escape
So that docstring text such as the following (in a code block) can be created ergonomically:
```rust
let s = "
foo
# bar
baz
";
```
Such code in a docstring hide the <code> # bar</code> line.
Previously, using two consecutive hashes <code> ## bar</code> would turn the line into _shown_ `# bar`, losing the leading whitespace. A line of code like <code> # bar</code> (such as in the example above) **could not be represented** in the docstring text.
This commit makes the two consecutive hashes not also trim the leading whitespace — the two hashes simply **escape** into a single hash and do not hide the line, leaving the rest of that line unaffected. The new docstring text to achieve the above code block is:
```rust
/// ```
/// let s = "
/// foo
/// ## bar
/// baz
/// ";
/// ```
```
rustdoc: import cross-crate macros alongside everything else
The thrilling conclusion of the cross-crate macro saga in rustdoc! After https://github.com/rust-lang/rust/pull/51425 made sure we saw all the namespaces of an import (and prevented us from losing the `vec!` macro in std's documentation), here is the PR to handle cross-crate macro re-exports at the same time as everything else. This way, attributes like `#[doc(hidden)]` and `#[doc(no_inline)]` can be used to control how the documentation for these macros is seen, rather than rustdoc inlining every macro every time.
Fixes https://github.com/rust-lang/rust/issues/50647
It was pointed out in review that the glob-exported
underscore-suffixed convention for `Spanned` HIR nodes is no longer
preferred: see February 2016's #31487 for AST's migration away from
this style towards properly namespaced NodeKind enums.
This concerns #51968.
There are at least a couple (and plausibly even three) diagnostics that
could use the spans of visibility modifiers in order to be reliably
correct (rather than hacking and munging surrounding spans to try to
infer where the visibility keyword must have been).
We follow the naming convention established by the other `Spanned` HIR
nodes: the "outer" type alias gets the "prime" node-type name, the
"inner" enum gets the name suffixed with an underscore, and the variant
names are prefixed with the prime name and `pub use` exported from here
(from HIR).
Thanks to veteran reviewer Vadim Petrochenkov for suggesting this
uniform approach. (A previous draft, based on the reasoning that
`Visibility::Inherited` should not have a span, tried to hack in a named
`span` field on `Visibility::Restricted` and a positional field on
`Public` and `Crate`. This was ... not so uniform.)
Namely: labels, type parameters, bindings in patterns, parameter names in functions without body.
All of these do not need hygiene after lowering to HIR, only span locations.
