Auto merge of #531 - ToMe25:optimize_is_disjoint, r=Amanieu

Optimize Set is_disjoint

By using the `Intersection` iterator in `HashSet::is_Disjoint` its performance can be significantly improved in some cases.
This is because `intersection()` always uses the shorter set as its iterator.

It would also be possible to replicate this "Iterate over the smaller set and check in the larger set" logic in the is_disjoint method.
However in my benchmarks the approach I chose is faster than that.

This change only causes a significant improvement when called on the larger of two disjoint sets.

My benchmark results:

Name | Before | After | Diff (%)
-- | -- | -- | --
disjoint_is_disjoint_large_small | 1,147.43 | 535.25 | -53,35 %
disjoint_is_disjoint_small_large | 535.66 | 527.59 | -1,51 %
subset_is_disjoint | 9.90 | 10.44 | 5,45 %
superset_is_disjoint | 9.80 | 10.43 | 6,43 %

Author: bors

src/raw/mod.rs

@@ -4439,11 +4439,13 @@ impl<T, A: Allocator> FusedIterator for RawDrain<'_, T, A> {}
 ///   created will be yielded by that iterator.
 /// - The order in which the iterator yields buckets is unspecified and may
 ///   change in the future.
+#[cfg(feature = "raw")]
 pub struct RawIterHash<T> {
     inner: RawIterHashInner,
     _marker: PhantomData<T>,
 }
 
+#[cfg(feature = "raw")]
 struct RawIterHashInner {
     // See `RawTableInner`'s corresponding fields for details.
     // We can't store a `*const RawTableInner` as it would get
@@ -4463,19 +4465,20 @@ struct RawIterHashInner {
     bitmask: BitMaskIter,
 }
 
+#[cfg(feature = "raw")]
 impl<T> RawIterHash<T> {
     #[cfg_attr(feature = "inline-more", inline)]
-    #[cfg(feature = "raw")]
     unsafe fn new<A: Allocator>(table: &RawTable<T, A>, hash: u64) -> Self {
         RawIterHash {
             inner: RawIterHashInner::new(&table.table, hash),
             _marker: PhantomData,
         }
     }
 }
+
+#[cfg(feature = "raw")]
 impl RawIterHashInner {
     #[cfg_attr(feature = "inline-more", inline)]
-    #[cfg(feature = "raw")]
     unsafe fn new(table: &RawTableInner, hash: u64) -> Self {
         let h2_hash = h2(hash);
         let probe_seq = table.probe_seq(hash);
@@ -4493,6 +4496,7 @@ impl RawIterHashInner {
     }
 }
 
+#[cfg(feature = "raw")]
 impl<T> Iterator for RawIterHash<T> {
     type Item = Bucket<T>;
 
@@ -4512,6 +4516,7 @@ impl<T> Iterator for RawIterHash<T> {
     }
 }
 
+#[cfg(feature = "raw")]
 impl Iterator for RawIterHashInner {
     type Item = usize;
 

src/set.rs

@@ -1044,7 +1044,7 @@ where
     /// assert_eq!(a.is_disjoint(&b), false);
     /// ```
     pub fn is_disjoint(&self, other: &Self) -> bool {
-        self.iter().all(|v| !other.contains(v))
+        self.intersection(other).next().is_none()
     }
 
     /// Returns `true` if the set is a subset of another,