maps,runtime: improve maps.Values

name       old time/op    new time/op    delta
Values-10    8.67ms ± 0%    7.19ms ± 2%  -17.05%  (p=0.000 n=9+10)

name       old alloc/op   new alloc/op   delta
Values-10    58.2kB ± 2%    48.3kB ± 2%  -17.14%  (p=0.000 n=9+10)

name       old allocs/op  new allocs/op  delta
Values-10      0.00           0.00          ~     (all equal)

Change-Id: Idd35ea37514a21d97bdd6191c8fb8a478c00e414
Reviewed-on: https://go-review.googlesource.com/c/go/+/481436
Reviewed-by: Keith Randall <khr@golang.org>
Run-TryBot: xie cui <523516579@qq.com>
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Keith Randall <khr@golang.org>

3 files changed, 102 insertions, 3 deletions

diff --git a/src/maps/maps.go b/src/maps/maps.go
index dddfb37973..15ec456a17 100644
--- a/src/maps/maps.go
+++ b/src/maps/maps.go
@@ -24,16 +24,23 @@ func keysForBenchmarking[M ~map[K]V, K comparable, V any](m M, s []K) {
 	keys(m, unsafe.Pointer(&s))
 }
 
+// values is implemented in the runtime package.
+//
+//go:noescape
+func values(m any, slice unsafe.Pointer)
+
 // Values returns the values of the map m.
 // The values will be in an indeterminate order.
 func Values[M ~map[K]V, K comparable, V any](m M) []V {
 	r := make([]V, 0, len(m))
-	for _, v := range m {
-		r = append(r, v)
-	}
+	values(m, unsafe.Pointer(&r))
 	return r
 }
 
+func valuesForBenchmarking[M ~map[K]V, K comparable, V any](m M, s []V) {
+	values(m, unsafe.Pointer(&s))
+}
+
 // Equal reports whether two maps contain the same key/value pairs.
 // Values are compared using ==.
 func Equal[M1, M2 ~map[K]V, K, V comparable](m1 M1, m2 M2) bool {
diff --git a/src/maps/maps_test.go b/src/maps/maps_test.go
index e7670839c9..6b92e0d8d6 100644
--- a/src/maps/maps_test.go
+++ b/src/maps/maps_test.go
@@ -62,6 +62,20 @@ func TestValues(t *testing.T) {
 	if !slices.Equal(got2, want2) {
 		t.Errorf("Values(%v) = %v, want %v", m2, got2, want2)
 	}
+
+	//test for oldbucket code path
+	var want3 []int
+	var m = make(map[int]int)
+	for i := 0; i < 840; i++ {
+		want3 = append(want3, i*i)
+		m[i] = i * i
+	}
+
+	got3 := Values(m)
+	sort.Ints(got3)
+	if !slices.Equal(got3, want3) {
+		t.Errorf("Values(%v) = %v, want %v", m, got3, want3)
+	}
 }
 
 func TestEqual(t *testing.T) {
@@ -246,3 +260,16 @@ func BenchmarkKeys(b *testing.B) {
 		keysForBenchmarking(m, slice)
 	}
 }
+
+func BenchmarkValues(b *testing.B) {
+	m := make(map[int]int, 1000000)
+	for i := 0; i < 1000000; i++ {
+		m[i] = i
+	}
+	b.ResetTimer()
+
+	slice := make([]int, 0, len(m))
+	for i := 0; i < b.N; i++ {
+		valuesForBenchmarking(m, slice)
+	}
+}
diff --git a/src/runtime/map.go b/src/runtime/map.go
index 33685269cd..7b954759f1 100644
--- a/src/runtime/map.go
+++ b/src/runtime/map.go
@@ -1657,3 +1657,68 @@ func copyKeys(t *maptype, h *hmap, b *bmap, s *slice, offset uint8) {
 		b = b.overflow(t)
 	}
 }
+
+// values for implementing maps.values
+//
+//go:linkname values maps.values
+func values(m any, p unsafe.Pointer) {
+	e := efaceOf(&m)
+	t := (*maptype)(unsafe.Pointer(e._type))
+	h := (*hmap)(e.data)
+	if h == nil || h.count == 0 {
+		return
+	}
+	s := (*slice)(p)
+	r := int(fastrand())
+	offset := uint8(r >> h.B & (bucketCnt - 1))
+	if h.B == 0 {
+		copyValues(t, h, (*bmap)(h.buckets), s, offset)
+		return
+	}
+	arraySize := int(bucketShift(h.B))
+	buckets := h.buckets
+	for i := 0; i < arraySize; i++ {
+		bucket := (i + r) & (arraySize - 1)
+		b := (*bmap)(add(buckets, uintptr(bucket)*uintptr(t.BucketSize)))
+		copyValues(t, h, b, s, offset)
+	}
+
+	if h.growing() {
+		oldArraySize := int(h.noldbuckets())
+		for i := 0; i < oldArraySize; i++ {
+			bucket := (i + r) & (oldArraySize - 1)
+			b := (*bmap)(add(h.oldbuckets, uintptr(bucket)*uintptr(t.BucketSize)))
+			if evacuated(b) {
+				continue
+			}
+			copyValues(t, h, b, s, offset)
+		}
+	}
+	return
+}
+
+func copyValues(t *maptype, h *hmap, b *bmap, s *slice, offset uint8) {
+	for b != nil {
+		for i := uintptr(0); i < bucketCnt; i++ {
+			offi := (i + uintptr(offset)) & (bucketCnt - 1)
+			if isEmpty(b.tophash[offi]) {
+				continue
+			}
+
+			if h.flags&hashWriting != 0 {
+				fatal("concurrent map read and map write")
+			}
+
+			ele := add(unsafe.Pointer(b), dataOffset+bucketCnt*uintptr(t.KeySize)+offi*uintptr(t.ValueSize))
+			if t.IndirectElem() {
+				ele = *((*unsafe.Pointer)(ele))
+			}
+			if s.len >= s.cap {
+				fatal("concurrent map read and map write")
+			}
+			typedmemmove(t.Elem, add(s.array, uintptr(s.len)*uintptr(t.ValueSize)), ele)
+			s.len++
+		}
+		b = b.overflow(t)
+	}
+}