Auto merge of #68827 - ssomers:btree_navigation_revisited, r=Mark-Sim…

…ulacrum BTreeMap navigation done safer & faster It turns out that there was a faster way to do the tree navigation code bundled in #67073, by moving from edge to KV and from KV to next edge separately. It extracts most of the code as safe functions, and contains the duplication of handles within the short wrapper functions. This somehow hits a sweet spot in the compiler because it reports boosts all over the board: ``` >cargo benchcmp pre3.txt posz4.txt --threshold 5 name pre3.txt ns/iter posz4.txt ns/iter diff ns/iter diff % speedup btree::map::first_and_last_0 40 37 -3 -7.50% x 1.08 btree::map::first_and_last_100 58 44 -14 -24.14% x 1.32 btree::map::iter_1000 8,920 3,419 -5,501 -61.67% x 2.61 btree::map::iter_100000 1,069,290 411,615 -657,675 -61.51% x 2.60 btree::map::iter_20 169 58 -111 -65.68% x 2.91 btree::map::iter_mut_1000 8,701 3,303 -5,398 -62.04% x 2.63 btree::map::iter_mut_100000 1,034,560 405,975 -628,585 -60.76% x 2.55 btree::map::iter_mut_20 165 58 -107 -64.85% x 2.84 btree::set::clone_100 1,831 1,562 -269 -14.69% x 1.17 btree::set::clone_100_and_clear 1,831 1,565 -266 -14.53% x 1.17 btree::set::clone_100_and_into_iter 1,917 1,541 -376 -19.61% x 1.24 btree::set::clone_100_and_pop_all 2,609 2,441 -168 -6.44% x 1.07 btree::set::clone_100_and_remove_all 4,598 3,927 -671 -14.59% x 1.17 btree::set::clone_100_and_remove_half 2,765 2,551 -214 -7.74% x 1.08 btree::set::clone_10k 191,610 164,616 -26,994 -14.09% x 1.16 btree::set::clone_10k_and_clear 192,003 164,616 -27,387 -14.26% x 1.17 btree::set::clone_10k_and_into_iter 200,037 163,010 -37,027 -18.51% x 1.23 btree::set::clone_10k_and_pop_all 267,023 250,913 -16,110 -6.03% x 1.06 btree::set::clone_10k_and_remove_all 536,230 464,100 -72,130 -13.45% x 1.16 btree::set::clone_10k_and_remove_half 453,350 430,545 -22,805 -5.03% x 1.05 btree::set::difference_random_100_vs_100 1,787 801 -986 -55.18% x 2.23 btree::set::difference_random_100_vs_10k 2,978 2,696 -282 -9.47% x 1.10 btree::set::difference_random_10k_vs_100 111,075 54,734 -56,341 -50.72% x 2.03 btree::set::difference_random_10k_vs_10k 246,380 175,980 -70,400 -28.57% x 1.40 btree::set::difference_staggered_100_vs_100 1,789 951 -838 -46.84% x 1.88 btree::set::difference_staggered_100_vs_10k 2,798 2,606 -192 -6.86% x 1.07 btree::set::difference_staggered_10k_vs_10k 176,452 97,401 -79,051 -44.80% x 1.81 btree::set::intersection_100_neg_vs_10k_pos 34 32 -2 -5.88% x 1.06 btree::set::intersection_100_pos_vs_100_neg 30 27 -3 -10.00% x 1.11 btree::set::intersection_random_100_vs_100 1,537 613 -924 -60.12% x 2.51 btree::set::intersection_random_100_vs_10k 2,793 2,649 -144 -5.16% x 1.05 btree::set::intersection_random_10k_vs_10k 222,127 147,166 -74,961 -33.75% x 1.51 btree::set::intersection_staggered_100_vs_100 1,447 622 -825 -57.01% x 2.33 btree::set::intersection_staggered_100_vs_10k 2,606 2,382 -224 -8.60% x 1.09 btree::set::intersection_staggered_10k_vs_10k 143,620 58,790 -84,830 -59.07% x 2.44 btree::set::is_subset_100_vs_100 1,349 488 -861 -63.83% x 2.76 btree::set::is_subset_100_vs_10k 1,720 1,428 -292 -16.98% x 1.20 btree::set::is_subset_10k_vs_10k 135,984 48,527 -87,457 -64.31% x 2.80 ``` The `first_and_last` ones are noise (they don't do iteration), the others seem genuine. As always, approved by Miri. Also, a separate commit with some more benchmarks of mutable behaviour (which also benefit). r? @cuviper
rust-lang · Feb 28, 2020 · e2223c9 · e2223c9
2 parents bfc32dd + 9f7b58f
commit e2223c9
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diff --git a/src/liballoc/benches/btree/set.rs b/src/liballoc/benches/btree/set.rs
@@ -50,43 +50,112 @@ macro_rules! set_bench {
     };
 }
 
-const BUILD_SET_SIZE: usize = 100;
+#[bench]
+pub fn clone_100(b: &mut Bencher) {
+    let src = pos(100);
+    b.iter(|| src.clone())
+}
 
 #[bench]
-pub fn build_and_clear(b: &mut Bencher) {
-    b.iter(|| pos(BUILD_SET_SIZE).clear())
+pub fn clone_100_and_clear(b: &mut Bencher) {
+    let src = pos(100);
+    b.iter(|| src.clone().clear())
 }
 
 #[bench]
-pub fn build_and_drop(b: &mut Bencher) {
-    b.iter(|| pos(BUILD_SET_SIZE))
+pub fn clone_100_and_into_iter(b: &mut Bencher) {
+    let src = pos(100);
+    b.iter(|| src.clone().into_iter().count())
 }
 
 #[bench]
-pub fn build_and_into_iter(b: &mut Bencher) {
-    b.iter(|| pos(BUILD_SET_SIZE).into_iter().count())
+pub fn clone_100_and_pop_all(b: &mut Bencher) {
+    let src = pos(100);
+    b.iter(|| {
+        let mut set = src.clone();
+        while set.pop_first().is_some() {}
+        set
+    });
 }
 
 #[bench]
-pub fn build_and_pop_all(b: &mut Bencher) {
+pub fn clone_100_and_remove_all(b: &mut Bencher) {
+    let src = pos(100);
     b.iter(|| {
-        let mut s = pos(BUILD_SET_SIZE);
-        while s.pop_first().is_some() {}
-        s
+        let mut set = src.clone();
+        while let Some(elt) = set.iter().copied().next() {
+            set.remove(&elt);
+        }
+        set
     });
 }
 
 #[bench]
-pub fn build_and_remove_all(b: &mut Bencher) {
+pub fn clone_100_and_remove_half(b: &mut Bencher) {
+    let src = pos(100);
     b.iter(|| {
-        let mut s = pos(BUILD_SET_SIZE);
-        while let Some(elt) = s.iter().copied().next() {
-            s.remove(&elt);
+        let mut set = src.clone();
+        for i in (2..=100 as i32).step_by(2) {
+            set.remove(&i);
         }
-        s
+        assert_eq!(set.len(), 100 / 2);
+        set
+    })
+}
+
+#[bench]
+pub fn clone_10k(b: &mut Bencher) {
+    let src = pos(10_000);
+    b.iter(|| src.clone())
+}
+
+#[bench]
+pub fn clone_10k_and_clear(b: &mut Bencher) {
+    let src = pos(10_000);
+    b.iter(|| src.clone().clear())
+}
+
+#[bench]
+pub fn clone_10k_and_into_iter(b: &mut Bencher) {
+    let src = pos(10_000);
+    b.iter(|| src.clone().into_iter().count())
+}
+
+#[bench]
+pub fn clone_10k_and_pop_all(b: &mut Bencher) {
+    let src = pos(10_000);
+    b.iter(|| {
+        let mut set = src.clone();
+        while set.pop_first().is_some() {}
+        set
+    });
+}
+
+#[bench]
+pub fn clone_10k_and_remove_all(b: &mut Bencher) {
+    let src = pos(10_000);
+    b.iter(|| {
+        let mut set = src.clone();
+        while let Some(elt) = set.iter().copied().next() {
+            set.remove(&elt);
+        }
+        set
     });
 }
 
+#[bench]
+pub fn clone_10k_and_remove_half(b: &mut Bencher) {
+    let src = pos(10_000);
+    b.iter(|| {
+        let mut set = src.clone();
+        for i in (2..=10_000 as i32).step_by(2) {
+            set.remove(&i);
+        }
+        assert_eq!(set.len(), 10_000 / 2);
+        set
+    })
+}
+
 set_bench! {intersection_100_neg_vs_100_pos, intersection, count, [neg(100), pos(100)]}
 set_bench! {intersection_100_neg_vs_10k_pos, intersection, count, [neg(100), pos(10_000)]}
 set_bench! {intersection_100_pos_vs_100_neg, intersection, count, [pos(100), neg(100)]}

diff --git a/src/liballoc/collections/btree/map.rs b/src/liballoc/collections/btree/map.rs
@@ -1487,16 +1487,13 @@ impl<K, V> Drop for IntoIter<K, V> {
         }
 
         unsafe {
-            let leaf_node = ptr::read(&self.front).into_node();
-            if leaf_node.is_shared_root() {
+            let mut node = ptr::read(&self.front).into_node().forget_type();
+            if node.is_shared_root() {
                 return;
             }
 
-            if let Some(first_parent) = leaf_node.deallocate_and_ascend() {
-                let mut cur_internal_node = first_parent.into_node();
-                while let Some(parent) = cur_internal_node.deallocate_and_ascend() {
-                    cur_internal_node = parent.into_node()
-                }
+            while let Some(parent) = node.deallocate_and_ascend() {
+                node = parent.into_node().forget_type();
             }
         }
     }