If we have
```rust
struct Foo<T: Copy = String> { .. }
```
the old code would have proven that `String: Copy` was WF -- this,
incidentally, also proved that `String: Copy`. The new code just
proves `String: Copy` directly.
Co-authored-by: Tyler Mandry <tmandry@gmail.com>
park/park_timeout: prohibit spurious wakeups in next park
<pre><code>
// The implementation currently uses the trivial strategy of a Mutex+Condvar
// with wakeup flag, which does not actually allow spurious wakeups.
</pre></code>
Because does not actually allow spurious wakeups.
so we have let thread.inner.cvar.wait(m) in the loop to prohibit spurious wakeups.
but if notified after we locked, this notification doesn't be consumed, it return, the next park will consume this notification...this is also 'spurious wakeup' case, 'one unpark() wakeups two park()'.
We should improve this situation：
`thread.inner.state.store(EMPTY, SeqCst);`
Arc: remove unused allocation from Weak::new()
It seems non-obvious that calling `Weak::new()` actually allocates space for the entire size of `T`, even though you can **never** access that data from such a constructed weak pointer. Besides that, if someone were to create many `Weak:new()`s, they could be unknowingly wasting a bunch of memory.
This change makes it so that `Weak::new()` allocates no memory at all. Instead, it is created with a null pointer. The only things done with a `Weak` are trying to upgrade, cloning, and dropping, meaning there are very few places that the code actually needs to check if the pointer is null.
Explicitely disable WASM code generation for Emscripten
Emscripten changed the default behavior recently:
bd050e64bb/ChangeLog.markdown (v1381-05172018)
It now defaults to WebAssembly and requires an explicit flag to generate asm.js.
WASM=0 is also valid for older emcc and thus doesn't break it.
Use assert_eq! in copy_from_slice
This will print both lengths when the assertion fails instead of just saying that they're different.
Output of current stable and nightly (modulo the exact line number):
```
thread 'main' panicked at 'destination and source slices have different lengths', libcore/slice/mod.rs:1645:9
```
Output after this PR:
```
thread 'main' panicked at 'assertion failed: `(left == right)`
left: `123`,
right: `456`: destination and source slices have different lengths', libcore/slice/mod.rs:1645:9
```
Note that I have not run the tests locally.
Optimize RefCell refcount tracking
Address the performance concern raised in https://github.com/rust-lang/rust/pull/51466#issuecomment-398255276
cc @dtolnay @nnethercote @rust-lang/wg-compiler-performance
cc @RalfJung @jhjourdan for soundness concerns
Can somebody kick off a perf run on this? I'm not sure how that's done, but I understand it has to be started manually.
The idea of this change is to switch to representing mutable refcount as values below 0 to eliminate some branching that was required with the old algorithm.
Emscripten changed the default behavior recently:
bd050e64bb/ChangeLog.markdown (v1381-05172018)
It now defaults to WebAssembly and requires an explicit flag to generate asm.js.
WASM=0 is also valid for older emcc and thus doesn't break it.
Closes#51856
Make FileMap::{lines, multibyte_chars, non_narrow_chars} non-mutable.
This PR removes most of the interior mutability from `FileMap`, which should be beneficial, especially in a multithreaded setting. This is achieved by initializing the state in question when the filemap is constructed instead of during lexing. Hopefully this doesn't degrade performance.
cc @wesleywiser
The method relied on the FileMap still being under construction in
order for it to do what the name promises. It's now independent of
the current state.
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.
Suggestion for 'static impl Trait return
When encountering a named or anonymous sup requirement (for example,
`&'a self`) and a `'static` impl Trait return type, suggest adding the
`'_` lifetime constraing to the return type.
Fix#43719, #51282.
```
error: cannot infer an appropriate lifetime
--> $DIR/static-return-lifetime-infered.rs:17:16
|
LL | fn iter_values_anon(&self) -> impl Iterator<Item=u32> {
| ----------------------- this return type evaluates to the `'static` lifetime...
LL | self.x.iter().map(|a| a.0)
| ------ ^^^^
| |
| ...but this borrow...
|
note: ...can't outlive the anonymous lifetime #1 defined on the method body at 16:5
--> $DIR/static-return-lifetime-infered.rs:16:5
|
LL | / fn iter_values_anon(&self) -> impl Iterator<Item=u32> {
LL | | self.x.iter().map(|a| a.0)
LL | | }
| |_____^
help: you can add a constraint to the return type to make it last less than `'static` and match the anonymous lifetime #1 defined on the method body at 16:5
|
LL | fn iter_values_anon(&self) -> impl Iterator<Item=u32> + '_ {
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
```
convert NLL ops to caches
This is a extension of <https://github.com/rust-lang/rust/pull/51460>. It uses a lot more caching than we used to do. This caching is not yet as efficient as it could be, but I'm curious to see the current perf results.
This is the high-level idea: in the MIR type checker, use [canonicalized queries](https://rust-lang-nursery.github.io/rustc-guide/traits/canonical-queries.html) for all the major operations. This is helpful because the MIR type check is operating in a context where all types are fully known (mostly, anyway) but regions are completely renumbered. This means we often wind up with duplicate queries like `Foo<'1, '2> :Bar` and `Foo<'3, '4>: Bar`. Canonicalized queries let us re-use the results. By the final commit in this PR, we can essentially just "read off" the resulting region relations and add them to the NLL type check.
Rollup of 7 pull requests
Successful merges:
- #49987 (Add str::split_ascii_whitespace.)
- #50342 (Document round-off error in `.mod_euc()`-method, see issue #50179)
- #51658 (Only do sanity check with debug assertions on)
- #51799 (Lower case some feature gate error messages)
- #51800 (Add a compiletest header for edition)
- #51824 (Fix the error reference for LocalKey::try_with)
- #51842 (Document that Layout::from_size_align does not allow align=0)
Failed merges:
r? @ghost
Fix the error reference for LocalKey::try_with
There's no such thing as `ThreadLocalError` and the method obviously returns `AccessError`, so adjusting (probably only outdated docs).
Add a compiletest header for edition
r? @nikomatsakis
Are the `-Zunstable-options` options needed in these tests? It looks like they aren't. If not, I can remove them.
Only do sanity check with debug assertions on
r? @nnethercote
I'm slighty confused. These changes address code that the `unused-warnings` benchmark doesn't go through, yet I see a 5% improvement to nightly on the `check` run, and no improvement on the other runs.
Maybe this change allows unrelated code in the same function to be better optimized?
