Optimize sum of Durations by using custom function
The current `impl Sum for Duration` uses `fold` to perform several `add`s (or really `checked_add`s) of durations. In doing so, it has to guarantee the number of nanoseconds is valid after every addition. If you squeese the current implementation into a single function it looks kind of like this:
````rust
fn sum<I: Iterator<Item = Duration>>(iter: I) -> Duration {
let mut sum = Duration::new(0, 0);
for rhs in iter {
if let Some(mut secs) = sum.secs.checked_add(rhs.secs) {
let mut nanos = sum.nanos + rhs.nanos;
if nanos >= NANOS_PER_SEC {
nanos -= NANOS_PER_SEC;
if let Some(new_secs) = secs.checked_add(1) {
secs = new_secs;
} else {
panic!("overflow when adding durations");
}
}
sum = Duration { secs, nanos }
} else {
panic!("overflow when adding durations");
}
}
sum
}
````
We only need to check if `nanos` is in the correct range when giving our final answer so we can have a more optimized version like so:
````rust
fn sum<I: Iterator<Item = Duration>>(iter: I) -> Duration {
let mut total_secs: u64 = 0;
let mut total_nanos: u64 = 0;
for entry in iter {
total_secs = total_secs
.checked_add(entry.secs)
.expect("overflow in iter::sum over durations");
total_nanos = match total_nanos.checked_add(entry.nanos as u64) {
Some(n) => n,
None => {
total_secs = total_secs
.checked_add(total_nanos / NANOS_PER_SEC as u64)
.expect("overflow in iter::sum over durations");
(total_nanos % NANOS_PER_SEC as u64) + entry.nanos as u64
}
};
}
total_secs = total_secs
.checked_add(total_nanos / NANOS_PER_SEC as u64)
.expect("overflow in iter::sum over durations");
total_nanos = total_nanos % NANOS_PER_SEC as u64;
Duration {
secs: total_secs,
nanos: total_nanos as u32,
}
}
````
We now only convert `total_nanos` to `total_secs` (1) if `total_nanos` overflows and (2) at the end of the function when we have to output a valid `Duration`. This gave a 5-22% performance improvement when I benchmarked it, depending on how big the `nano` value of the `Duration`s in `iter` were.
This is a different approach to #51672 as suggested by @oli-obk. Rather
than write each repeated value one-by-one, we write the first one and
then copy its value directly into the remaining memory.
Don't inspect the generated existential type items
r? @nikomatsakis
My debugging led me to the `hir::ItemExistential(..)` checks, which are entirely unnecessary because we never use the items directly. The issue was that items were iterated over in a random order (due to hashmaps), so if you checked the `ItemExistential` before the function that has the actual return `impl Trait`, you'd run into those ICEs you encountered.
lint to favor `..=` over `...` range patterns; migrate to `..=` throughout codebase
We probably need an RFC to actually deprecate the `...` syntax, but here's a candidate implementation for the lint considered in #51043. (My local build is super flaky, but hopefully I got all of the test revisions.)
Add `LocalTaskObj` to `core::task`
- Splits `libcore/task.rs` into submodules
- Adds `LocalTaskObj` and `SpawnLocalObjError` (-> [Commit for this](433e6b31a7))
Note: To make reviewing easy, both actions have their own commit
r? @cramertj
Do not build LLVM tools for any of the tools
None of the tools in the list should need LLVM tools themselves as far as I can
tell; if this is incorrect, we can re-enable the tool building later.
The primary reason for doing this is that rust-central-station uses the
BuildManifest tool and building LLVM there is not cached: it takes ~1.5
hours on the 2 core machine. This commit should make nightlies and
stable releases much faster.
Followup to https://github.com/rust-lang/rust/pull/51459, r? @kennytm
I'm mostly relying on CI to test this so probably don't roll it up; I'm not sure how to (and not particularly inclined to) wait for multiple hours to test this locally. I imagine that the failures should be fairly obvious when/if encountered.
As the comment explains, this is needed to prevent subtype from going
awry in higher-ranked cases, due to #33684. The proper fix here is
introducing universes (#48536).
