3 files changed, 108 insertions, 6 deletions

diff --git a/src/reflect/all_test.go b/src/reflect/all_test.go
index 293d036f67..e92f71135c 100644
--- a/src/reflect/all_test.go
+++ b/src/reflect/all_test.go
@@ -7050,6 +7050,53 @@ func BenchmarkNew(b *testing.B) {
 	})
 }
 
+func BenchmarkMap(b *testing.B) {
+	type V *int
+	value := ValueOf((V)(nil))
+	stringKeys := []string{}
+	mapOfStrings := map[string]V{}
+	uint64Keys := []uint64{}
+	mapOfUint64s := map[uint64]V{}
+	for i := 0; i < 100; i++ {
+		stringKey := fmt.Sprintf("key%d", i)
+		stringKeys = append(stringKeys, stringKey)
+		mapOfStrings[stringKey] = nil
+
+		uint64Key := uint64(i)
+		uint64Keys = append(uint64Keys, uint64Key)
+		mapOfUint64s[uint64Key] = nil
+	}
+
+	tests := []struct {
+		label          string
+		m, keys, value Value
+	}{
+		{"StringKeys", ValueOf(mapOfStrings), ValueOf(stringKeys), value},
+		{"Uint64Keys", ValueOf(mapOfUint64s), ValueOf(uint64Keys), value},
+	}
+
+	for _, tt := range tests {
+		b.Run(tt.label, func(b *testing.B) {
+			b.Run("MapIndex", func(b *testing.B) {
+				b.ReportAllocs()
+				for i := 0; i < b.N; i++ {
+					for j := tt.keys.Len() - 1; j >= 0; j-- {
+						tt.m.MapIndex(tt.keys.Index(j))
+					}
+				}
+			})
+			b.Run("SetMapIndex", func(b *testing.B) {
+				b.ReportAllocs()
+				for i := 0; i < b.N; i++ {
+					for j := tt.keys.Len() - 1; j >= 0; j-- {
+						tt.m.SetMapIndex(tt.keys.Index(j), tt.value)
+					}
+				}
+			})
+		})
+	}
+}
+
 func TestSwapper(t *testing.T) {
 	type I int
 	var a, b, c I
diff --git a/src/reflect/value.go b/src/reflect/value.go
index bf29d1bb3a..6e9aaabe8a 100644
--- a/src/reflect/value.go
+++ b/src/reflect/value.go
@@ -1515,15 +1515,21 @@ func (v Value) MapIndex(key Value) Value {
 	// considered unexported. This is consistent with the
 	// behavior for structs, which allow read but not write
 	// of unexported fields.
-	key = key.assignTo("reflect.Value.MapIndex", tt.key, nil)
 
-	var k unsafe.Pointer
-	if key.flag&flagIndir != 0 {
-		k = key.ptr
+	var e unsafe.Pointer
+	if key.kind() == String && tt.key.Kind() == String {
+		k := *(*string)(key.ptr)
+		e = mapaccess_faststr(v.typ, v.pointer(), k)
 	} else {
-		k = unsafe.Pointer(&key.ptr)
+		key = key.assignTo("reflect.Value.MapIndex", tt.key, nil)
+		var k unsafe.Pointer
+		if key.flag&flagIndir != 0 {
+			k = key.ptr
+		} else {
+			k = unsafe.Pointer(&key.ptr)
+		}
+		e = mapaccess(v.typ, v.pointer(), k)
 	}
-	e := mapaccess(v.typ, v.pointer(), k)
 	if e == nil {
 		return Value{}
 	}
@@ -2121,6 +2127,25 @@ func (v Value) SetMapIndex(key, elem Value) {
 	v.mustBeExported()
 	key.mustBeExported()
 	tt := (*mapType)(unsafe.Pointer(v.typ))
+
+	if key.kind() == String && tt.key.Kind() == String {
+		k := *(*string)(key.ptr)
+		if elem.typ == nil {
+			mapdelete_faststr(v.typ, v.pointer(), k)
+			return
+		}
+		elem.mustBeExported()
+		elem = elem.assignTo("reflect.Value.SetMapIndex", tt.elem, nil)
+		var e unsafe.Pointer
+		if elem.flag&flagIndir != 0 {
+			e = elem.ptr
+		} else {
+			e = unsafe.Pointer(&elem.ptr)
+		}
+		mapassign_faststr(v.typ, v.pointer(), k, e)
+		return
+	}
+
 	key = key.assignTo("reflect.Value.SetMapIndex", tt.key, nil)
 	var k unsafe.Pointer
 	if key.flag&flagIndir != 0 {
@@ -3253,12 +3278,21 @@ func makemap(t *rtype, cap int) (m unsafe.Pointer)
 func mapaccess(t *rtype, m unsafe.Pointer, key unsafe.Pointer) (val unsafe.Pointer)
 
 //go:noescape
+func mapaccess_faststr(t *rtype, m unsafe.Pointer, key string) (val unsafe.Pointer)
+
+//go:noescape
 func mapassign(t *rtype, m unsafe.Pointer, key, val unsafe.Pointer)
 
 //go:noescape
+func mapassign_faststr(t *rtype, m unsafe.Pointer, key string, val unsafe.Pointer)
+
+//go:noescape
 func mapdelete(t *rtype, m unsafe.Pointer, key unsafe.Pointer)
 
 //go:noescape
+func mapdelete_faststr(t *rtype, m unsafe.Pointer, key string)
+
+//go:noescape
 func mapiterinit(t *rtype, m unsafe.Pointer, it *hiter)
 
 //go:noescape
diff --git a/src/runtime/map.go b/src/runtime/map.go
index 59b803d629..985c297cd4 100644
--- a/src/runtime/map.go
+++ b/src/runtime/map.go
@@ -1324,17 +1324,38 @@ func reflect_mapaccess(t *maptype, h *hmap, key unsafe.Pointer) unsafe.Pointer {
 	return elem
 }
 
+//go:linkname reflect_mapaccess_faststr reflect.mapaccess_faststr
+func reflect_mapaccess_faststr(t *maptype, h *hmap, key string) unsafe.Pointer {
+	elem, ok := mapaccess2_faststr(t, h, key)
+	if !ok {
+		// reflect wants nil for a missing element
+		elem = nil
+	}
+	return elem
+}
+
 //go:linkname reflect_mapassign reflect.mapassign
 func reflect_mapassign(t *maptype, h *hmap, key unsafe.Pointer, elem unsafe.Pointer) {
 	p := mapassign(t, h, key)
 	typedmemmove(t.elem, p, elem)
 }
 
+//go:linkname reflect_mapassign_faststr reflect.mapassign_faststr
+func reflect_mapassign_faststr(t *maptype, h *hmap, key string, elem unsafe.Pointer) {
+	p := mapassign_faststr(t, h, key)
+	typedmemmove(t.elem, p, elem)
+}
+
 //go:linkname reflect_mapdelete reflect.mapdelete
 func reflect_mapdelete(t *maptype, h *hmap, key unsafe.Pointer) {
 	mapdelete(t, h, key)
 }
 
+//go:linkname reflect_mapdelete_faststr reflect.mapdelete_faststr
+func reflect_mapdelete_faststr(t *maptype, h *hmap, key string) {
+	mapdelete_faststr(t, h, key)
+}
+
 //go:linkname reflect_mapiterinit reflect.mapiterinit
 func reflect_mapiterinit(t *maptype, h *hmap, it *hiter) {
 	mapiterinit(t, h, it)