maps,runtime: improve maps.Keys

name     old time/op    new time/op    delta
Keys-10    8.65ms ± 0%    7.06ms ± 0%  -18.41%  (p=0.000 n=9+9)

name     old alloc/op   new alloc/op   delta
Keys-10    58.2kB ± 1%    47.4kB ± 2%  -18.54%  (p=0.000 n=10+10)

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

Change-Id: Ia7061c37be89e906e79bc3ef3bb1ef0d7913f9f6
Reviewed-on: https://go-review.googlesource.com/c/go/+/481435
Reviewed-by: Keith Randall <khr@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Heschi Kreinick <heschi@google.com>
Run-TryBot: xie cui <523516579@qq.com>

1 files changed, 64 insertions, 0 deletions

diff --git a/src/runtime/map.go b/src/runtime/map.go
index a1fe08f758..33685269cd 100644
--- a/src/runtime/map.go
+++ b/src/runtime/map.go
@@ -1593,3 +1593,67 @@ func mapclone2(t *maptype, src *hmap) *hmap {
 	}
 	return dst
 }
+
+// keys for implementing maps.keys
+//
+//go:linkname keys maps.keys
+func keys(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 {
+		copyKeys(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)))
+		copyKeys(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
+			}
+			copyKeys(t, h, b, s, offset)
+		}
+	}
+	return
+}
+
+func copyKeys(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")
+			}
+			k := add(unsafe.Pointer(b), dataOffset+offi*uintptr(t.KeySize))
+			if t.IndirectKey() {
+				k = *((*unsafe.Pointer)(k))
+			}
+			if s.len >= s.cap {
+				fatal("concurrent map read and map write")
+			}
+			typedmemmove(t.Key, add(s.array, uintptr(s.len)*uintptr(t.KeySize)), k)
+			s.len++
+		}
+		b = b.overflow(t)
+	}
+}