golang
diff --git a/‎src/cmd/compile/internal/gc/builtin.go
+3 b/‎src/cmd/compile/internal/gc/builtin.go
+3
diff --git a/‎src/cmd/compile/internal/gc/builtin/runtime.go
+3 b/‎src/cmd/compile/internal/gc/builtin/runtime.go
+3
diff --git a/‎src/cmd/compile/internal/gc/order.go
+12-5 b/‎src/cmd/compile/internal/gc/order.go
+12-5
diff --git a/‎src/cmd/compile/internal/gc/walk.go
+26-4 b/‎src/cmd/compile/internal/gc/walk.go
+26-4
@@ -83,6 +83,9 @@ var runtimeDecls = [...]struct {
 	{"mapaccess2_faststr", funcTag, 64},
 	{"mapaccess2_fat", funcTag, 65},
 	{"mapassign", funcTag, 60},
+	{"mapassign_fast32", funcTag, 61},
+	{"mapassign_fast64", funcTag, 61},
+	{"mapassign_faststr", funcTag, 61},
 	{"mapiterinit", funcTag, 66},
 	{"mapdelete", funcTag, 66},
 	{"mapiternext", funcTag, 67},
 
@@ -103,6 +103,9 @@ func mapaccess2_fast64(mapType *byte, hmap map[any]any, key any) (val *any, pres
 func mapaccess2_faststr(mapType *byte, hmap map[any]any, key any) (val *any, pres bool)
 func mapaccess2_fat(mapType *byte, hmap map[any]any, key *any, zero *byte) (val *any, pres bool)
 func mapassign(mapType *byte, hmap map[any]any, key *any) (val *any)
+func mapassign_fast32(mapType *byte, hmap map[any]any, key any) (val *any)
+func mapassign_fast64(mapType *byte, hmap map[any]any, key any) (val *any)
+func mapassign_faststr(mapType *byte, hmap map[any]any, key any) (val *any)
 func mapiterinit(mapType *byte, hmap map[any]any, hiter *any)
 func mapdelete(mapType *byte, hmap map[any]any, key *any)
 func mapiternext(hiter *any)
 
@@ -206,13 +206,20 @@ func orderaddrtemp(n *Node, order *Order) *Node {
 	return ordercopyexpr(n, n.Type, order, 0)
 }
 
-// ordermapkeytemp prepares n.Right to be a key in a map lookup.
+// ordermapkeytemp prepares n.Right to be a key in a map runtime call.
 func ordermapkeytemp(n *Node, order *Order) {
 	// Most map calls need to take the address of the key.
-	// Exception: mapaccessN_fast* calls. See golang.org/issue/19015.
-	p, _ := mapaccessfast(n.Left.Type)
-	fastaccess := p != "" && n.Etype == 0 // Etype == 0 iff n is an rvalue
-	if fastaccess {
+	// Exception: map(accessN|assign)_fast* calls. See golang.org/issue/19015.
+	var p string
+	switch n.Etype {
+	case 0: // n is an rvalue
+		p, _ = mapaccessfast(n.Left.Type)
+	case 1: // n is an lvalue
+		p = mapassignfast(n.Left.Type)
+	default:
+		Fatalf("unexpected node type: %+v", n)
+	}
+	if p != "" {
 		return
 	}
 	n.Right = orderaddrtemp(n.Right, order)
 
@@ -1184,9 +1184,14 @@ opswitch:
 		t := map_.Type
 		if n.Etype == 1 {
 			// This m[k] expression is on the left-hand side of an assignment.
-			// orderexpr made sure key is addressable.
-			key = nod(OADDR, key, nil)
-			n = mkcall1(mapfn("mapassign", t), nil, init, typename(t), map_, key)
+			p := mapassignfast(t)
+			if p == "" {
+				// standard version takes key by reference.
+				// orderexpr made sure key is addressable.
+				key = nod(OADDR, key, nil)
+				p = "mapassign"
+			}
+			n = mkcall1(mapfn(p, t), nil, init, typename(t), map_, key)
 		} else {
 			// m[k] is not the target of an assignment.
 			p, _ := mapaccessfast(t)
@@ -2628,7 +2633,7 @@ func mapfndel(name string, t *Type) *Node {
 	return fn
 }
 
-// mapaccessfast returns the names of the fast map access runtime routines for t.
+// mapaccessfast returns the name of the fast map access runtime routine for t.
 func mapaccessfast(t *Type) (access1, access2 string) {
 	// Check ../../runtime/hashmap.go:maxValueSize before changing.
 	if t.Val().Width > 128 {
@@ -2645,6 +2650,23 @@ func mapaccessfast(t *Type) (access1, access2 string) {
 	return "", ""
 }
 
+// mapassignfast returns the name of the fast map assign runtime routine for t.
+func mapassignfast(t *Type) (assign string) {
+	// Check ../../runtime/hashmap.go:maxValueSize before changing.
+	if t.Val().Width > 128 {
+		return ""
+	}
+	switch algtype(t.Key()) {
+	case AMEM32:
+		return "mapassign_fast32"
+	case AMEM64:
+		return "mapassign_fast64"
+	case ASTRING:
+		return "mapassign_faststr"
+	}
+	return ""
+}
+
 func writebarrierfn(name string, l *Type, r *Type) *Node {
 	fn := syslook(name)
 	fn = substArgTypes(fn, l, r)