Rollup of 8 pull requests #41116
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Rollup of 8 pull requests #41116
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frewsxcv
commented
Apr 6, 2017
frewsxcv
commented
- Successful merges: #[used] attribute #39987, Introduce HashStable trait and base ICH implementations on it. #40878, Only use cargo-vendor if building from git sources #41047, travis: Update musl for i686/x86_64 #41089, Add example to std::process::abort #41090, Fix Markdown issues in the docs #41111, rustdoc: Use pulldown-cmark for Markdown HTML rendering #41112, .gitmodules: use the official Git URL w/o redirect #41114
- Failed merges:
This is a random stab towards rust-lang#38618, no idea if it'll work. But hey more up-to-date software is better, right?
similar to GCC's __attribute((used))__. This attribute prevents LLVM from
optimizing away a non-exported symbol, within a compilation unit (object file),
when there are no references to it.
This is better explained with an example:
```
#[used]
static LIVE: i32 = 0;
static REFERENCED: i32 = 0;
static DEAD: i32 = 0;
fn internal() {}
pub fn exported() -> &'static i32 {
&REFERENCED
}
```
Without optimizations, LLVM pretty much preserves all the static variables and
functions within the compilation unit.
```
$ rustc --crate-type=lib --emit=obj symbols.rs && nm -C symbols.o
0000000000000000 t drop::h1be0f8f27a2ba94a
0000000000000000 r symbols::REFERENCED::hb3bdfd46050bc84c
0000000000000000 r symbols::DEAD::hc2ea8f9bd06f380b
0000000000000000 r symbols::LIVE::h0970cf9889edb56e
0000000000000000 T symbols::exported::h6f096c2b1fc292b2
0000000000000000 t symbols::internal::h0ac1aadbc1e3a494
```
With optimizations, LLVM will drop dead code. Here `internal` is dropped because
it's not a exported function/symbol (i.e. not `pub`lic). `DEAD` is dropped for
the same reason. `REFERENCED` is preserved, even though it's not exported,
because it's referenced by the `exported` function. Finally, `LIVE` survives
because of the `#[used]` attribute even though it's not exported or referenced.
```
$ rustc --crate-type=lib -C opt-level=3 --emit=obj symbols.rs && nm -C symbols.o
0000000000000000 r symbols::REFERENCED::hb3bdfd46050bc84c
0000000000000000 r symbols::LIVE::h0970cf9889edb56e
0000000000000000 T symbols::exported::h6f096c2b1fc292b2
```
Note that the linker knows nothing about `#[used]` and will drop `LIVE`
because no other object references to it.
```
$ echo 'fn main() {}' >> symbols.rs
$ rustc symbols.rs && nm -C symbols | grep LIVE
```
At this time, `#[used]` only works on `static` variables.
This is a second (2/3?) step in order to complete this issue: rust-lang#29370 I submitted this PR with the help of @steveklabnik again. Thanks to him! More info here: rust-lang#29370 (comment)
to match the type signature of the llvm.used variable
it's not related to this feature
* Since the switch to pulldown-cmark reference links need a blank line before the URLs. * Reference link references are not case sensitive. * Doc comments need to be indented uniformly otherwise rustdoc gets confused.
Instead of rendering all of the HTML in rustdoc this relies on pulldown-cmark's `push_html` to do most of the work. A few iterator adapters are used to make rustdoc specific modifications to the output. This also fixes MarkdownHtml and link titles in plain_summary_line.
This initial commit provides implementations for HIR, MIR, and everything that also needs to be supported for those two.
(For an explanation of what this feature does, read the commit message)
I'd like to propose landing this as an experimental feature (experimental as in:
no clear stabilization path -- like `asm!`, `#[linkage]`) as it's low
maintenance (I think) and relevant to the "Usage in resource-constrained
environments" exploration area.
The main use case I see is running code before `main`. This could be used, for
instance, to cheaply initialize an allocator before `main` where the alternative
is to use `lazy_static` to initialize the allocator on its first use which it's
more expensive (atomics) and doesn't work on ARM Cortex-M0 microcontrollers (no
`AtomicUsize` on that platform)
Here's a `std` example of that:
``` rust
unsafe extern "C" fn before_main_1() {
println!("Hello");
}
unsafe extern "C" fn before_main_2() {
println!("World");
}
static INIT_ARRAY: [unsafe extern "C" fn(); 2] = [before_main_1, before_main_2];
fn main() {
println!("Goodbye");
}
```
```
$ rustc -C lto -C opt-level=3 before_main.rs
$ ./before_main
Hello
World
Goodbye
```
In general, this pattern could be used to let *dependencies* run code before
`main` (which sounds like it could go very wrong in some cases). There are
probably other use cases; I hope that the people I have cc-ed can comment on
those.
Note that I'm personally unsure if the above pattern is something we want to
promote / allow and that's why I'm proposing this feature as experimental. If
this leads to more footguns than benefits then we can just axe the feature.
cc @nikomatsakis ^ I know you have some thoughts on having a process for
experimental features though I'm fine with writing an RFC before landing this.
- `dead_code` lint will have to be updated to special case `#[used]` symbols.
- Should we extend `#[used]` to work on non-generic functions?
cc rust-lang/rfcs#1002
cc rust-lang/rfcs#1459
cc @dpc @JinShil
Introduce HashStable trait and base ICH implementations on it. This PR introduces the `HashStable` trait which marks that a type can be hashed in a way that is stable across multiple compilation sessions. The PR also moves HIR incr. comp. hashing over to implementations of this trait instead of doing this via a HIR visitor. It also provides many `HashStable` implementations that are not used yet (e.g. for MIR types) but soon will be used when we directly hash crate metadata for incr. comp. I've only done superficial performance measurements but it looks like the new implementation is a bit faster than the current one (due, I suppose, to some bugs I fixed and some unnecessary inefficiencies I removed). Here is the time in seconds for the `compute_incremental_hashes_map` pass for various crates: | | OLD | NEW | |:---------------:|:-----:|:-----:| | libcore | 0.507 | 0.409 | | libsyntax | 0.320 | 0.260 | | librustc | 0.730 | 0.611 | | librustc_driver | 0.024 | 0.015 | Some notes regarding the implementation: * Most `HashStable` implementations are provided via the `impl_hash_stable_for!` macro (as suggested by @nikomatsakis). This works out quite well. A custom_derive would have been better but Macros 1.1 are not available in the compiler. * The trait implementation take care to exhaustively destructure everything they hash so that fields added in the future don't fall through the cracks. This is a bit verbose but I think it's well worth the trouble since we've had quite a few issues with missing fields or visitor callbacks in this area in the past. Most of it is behind the macro anyway. cc @rust-lang/compiler r? @nikomatsakis
Only use cargo-vendor if building from git sources The only time we need to vendor sources is when building from git. If one is building from a rustc source tarball, everything should already be in place. This also matters for distros which do offline builds, as they can't install cargo-vendor this way. This adds a common `Build::src_is_git` flag, and then uses it in the dist-src target to decide whether to install or use `cargo-vendor` at all. Fixes rust-lang#41042.
travis: Update musl for i686/x86_64 This is a random stab towards rust-lang#38618, no idea if it'll work. But hey more up-to-date software is better, right?
Add example to std::process::abort This is a second step in order to complete this issue: rust-lang#29370 I submitted this PR with the help of @steveklabnik again. Thanks to him! More info here: rust-lang#29370 (comment)
…umeGomez Fix Markdown issues in the docs * Since the switch to pulldown-cmark reference links need a blank line before the URLs. (rust-lang#40912) * Reference link references are not case sensitive. * Doc comments need to be indented uniformly otherwise rustdoc gets confused.
rustdoc: Use pulldown-cmark for Markdown HTML rendering Instead of rendering all of the HTML in rustdoc this relies on pulldown-cmark's `push_html` to do most of the work. A few iterator adapters are used to make rustdoc specific modifications to the output. This also fixes MarkdownHtml and link titles in plain_summary_line. https://ollie27.github.io/rust_doc_test/ is the docs built with this change and rust-lang#41111. Part of rust-lang#40912. cc @GuillaumeGomez r? @steveklabnik
.gitmodules: use the official Git URL w/o redirect
|
Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @nrc (or someone else) soon. If any changes to this PR are deemed necessary, please add them as extra commits. This ensures that the reviewer can see what has changed since they last reviewed the code. Due to the way GitHub handles out-of-date commits, this should also make it reasonably obvious what issues have or haven't been addressed. Large or tricky changes may require several passes of review and changes. Please see the contribution instructions for more information. |
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@bors r+ p=10 |
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📌 Commit ad59ff8 has been approved by |
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⌛ Testing commit ad59ff8 with merge 5d5e056... |
|
💔 Test failed - status-travis |
|
⌛ Testing commit ad59ff8 with merge 8981bc1... |
|
💔 Test failed - status-travis |
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