diff --git a/src/cmd/compile/internal/gc/builtin.go b/src/cmd/compile/internal/gc/builtin.go
index eafdb0e..861ffaa 100644
--- a/src/cmd/compile/internal/gc/builtin.go
+++ b/src/cmd/compile/internal/gc/builtin.go
@@ -302,7 +302,7 @@
 	typs[96] = types.NewPtr(typs[6])
 	typs[97] = functype(nil, []*Node{anonfield(typs[3]), anonfield(typs[96]), anonfield(typs[84])}, []*Node{anonfield(typs[6])})
 	typs[98] = functype(nil, []*Node{anonfield(typs[63])}, nil)
-	typs[99] = functype(nil, []*Node{anonfield(typs[1]), anonfield(typs[1]), anonfield(typs[63]), anonfield(typs[15])}, []*Node{anonfield(typs[15]), anonfield(typs[6])})
+	typs[99] = functype(nil, []*Node{anonfield(typs[1]), anonfield(typs[1]), anonfield(typs[63]), anonfield(typs[15]), anonfield(typs[15]), anonfield(typs[6])}, []*Node{anonfield(typs[15]), anonfield(typs[6])})
 	typs[100] = functype(nil, []*Node{anonfield(typs[1]), anonfield(typs[15]), anonfield(typs[15])}, []*Node{anonfield(typs[7])})
 	typs[101] = functype(nil, []*Node{anonfield(typs[1]), anonfield(typs[22]), anonfield(typs[22])}, []*Node{anonfield(typs[7])})
 	typs[102] = functype(nil, []*Node{anonfield(typs[1]), anonfield(typs[15]), anonfield(typs[15]), anonfield(typs[7])}, []*Node{anonfield(typs[7])})
diff --git a/src/cmd/compile/internal/gc/builtin/runtime.go b/src/cmd/compile/internal/gc/builtin/runtime.go
index 25f86ef..635da80 100644
--- a/src/cmd/compile/internal/gc/builtin/runtime.go
+++ b/src/cmd/compile/internal/gc/builtin/runtime.go
@@ -170,7 +170,7 @@
 func selectnbrecv2(elem *any, received *bool, hchan <-chan any) bool
 
 func selectsetpc(pc *uintptr)
-func selectgo(cas0 *byte, order0 *byte, pc0 *uintptr, ncases int) (int, bool)
+func selectgo(cas0 *byte, order0 *byte, pc0 *uintptr, nsends int, nrecvs int, block bool) (int, bool)
 func block()
 
 func makeslice(typ *byte, len int, cap int) unsafe.Pointer
diff --git a/src/cmd/compile/internal/gc/select.go b/src/cmd/compile/internal/gc/select.go
index 8eb31eb..bae7ed3 100644
--- a/src/cmd/compile/internal/gc/select.go
+++ b/src/cmd/compile/internal/gc/select.go
@@ -106,18 +106,16 @@
 }
 
 func walkselectcases(cases *Nodes) []*Node {
-	n := cases.Len()
+	ncas := cases.Len()
 	sellineno := lineno
 
 	// optimization: zero-case select
-	if n == 0 {
+	if ncas == 0 {
 		return []*Node{mkcall("block", nil, nil)}
 	}
 
 	// optimization: one-case select: single op.
-	// TODO(rsc): Reenable optimization once order.go can handle it.
-	// golang.org/issue/7672.
-	if n == 1 {
+	if ncas == 1 {
 		cas := cases.First()
 		setlineno(cas)
 		l := cas.Ninit.Slice()
@@ -178,10 +176,12 @@
 
 	// convert case value arguments to addresses.
 	// this rewrite is used by both the general code and the next optimization.
+	var dflt *Node
 	for _, cas := range cases.Slice() {
 		setlineno(cas)
 		n := cas.Left
 		if n == nil {
+			dflt = cas
 			continue
 		}
 		switch n.Op {
@@ -202,15 +202,10 @@
 	}
 
 	// optimization: two-case select but one is default: single non-blocking op.
-	if n == 2 && (cases.First().Left == nil || cases.Second().Left == nil) {
-		var cas *Node
-		var dflt *Node
-		if cases.First().Left == nil {
+	if ncas == 2 && dflt != nil {
+		cas := cases.First()
+		if cas == dflt {
 			cas = cases.Second()
-			dflt = cases.First()
-		} else {
-			dflt = cases.Second()
-			cas = cases.First()
 		}
 
 		n := cas.Left
@@ -257,74 +252,73 @@
 		return []*Node{r, nod(OBREAK, nil, nil)}
 	}
 
+	if dflt != nil {
+		ncas--
+	}
+	casorder := make([]*Node, ncas)
+	nsends, nrecvs := 0, 0
+
 	var init []*Node
 
 	// generate sel-struct
 	lineno = sellineno
-	selv := temp(types.NewArray(scasetype(), int64(n)))
+	selv := temp(types.NewArray(scasetype(), int64(ncas)))
 	r := nod(OAS, selv, nil)
 	r = typecheck(r, ctxStmt)
 	init = append(init, r)
 
-	order := temp(types.NewArray(types.Types[TUINT16], 2*int64(n)))
+	order := temp(types.NewArray(types.Types[TUINT16], 2*int64(ncas)))
 	r = nod(OAS, order, nil)
 	r = typecheck(r, ctxStmt)
 	init = append(init, r)
 
 	var pc0, pcs *Node
 	if flag_race {
-		pcs = temp(types.NewArray(types.Types[TUINTPTR], int64(n)))
+		pcs = temp(types.NewArray(types.Types[TUINTPTR], int64(ncas)))
 		pc0 = typecheck(nod(OADDR, nod(OINDEX, pcs, nodintconst(0)), nil), ctxExpr)
 	} else {
 		pc0 = nodnil()
 	}
 
 	// register cases
-	for i, cas := range cases.Slice() {
+	for _, cas := range cases.Slice() {
 		setlineno(cas)
 
 		init = append(init, cas.Ninit.Slice()...)
 		cas.Ninit.Set(nil)
 
-		// Keep in sync with runtime/select.go.
-		const (
-			caseNil = iota
-			caseRecv
-			caseSend
-			caseDefault
-		)
-
-		var c, elem *Node
-		var kind int64 = caseDefault
-
-		if n := cas.Left; n != nil {
-			init = append(init, n.Ninit.Slice()...)
-
-			switch n.Op {
-			default:
-				Fatalf("select %v", n.Op)
-			case OSEND:
-				kind = caseSend
-				c = n.Left
-				elem = n.Right
-			case OSELRECV, OSELRECV2:
-				kind = caseRecv
-				c = n.Right.Left
-				elem = n.Left
-			}
+		n := cas.Left
+		if n == nil { // default:
+			continue
 		}
 
+		var i int
+		var c, elem *Node
+		switch n.Op {
+		default:
+			Fatalf("select %v", n.Op)
+		case OSEND:
+			i = nsends
+			nsends++
+			c = n.Left
+			elem = n.Right
+		case OSELRECV, OSELRECV2:
+			nrecvs++
+			i = ncas - nrecvs
+			c = n.Right.Left
+			elem = n.Left
+		}
+
+		casorder[i] = cas
+
 		setField := func(f string, val *Node) {
 			r := nod(OAS, nodSym(ODOT, nod(OINDEX, selv, nodintconst(int64(i))), lookup(f)), val)
 			r = typecheck(r, ctxStmt)
 			init = append(init, r)
 		}
 
-		setField("kind", nodintconst(kind))
-		if c != nil {
-			c = convnop(c, types.Types[TUNSAFEPTR])
-			setField("c", c)
-		}
+		c = convnop(c, types.Types[TUNSAFEPTR])
+		setField("c", c)
 		if elem != nil {
 			elem = convnop(elem, types.Types[TUNSAFEPTR])
 			setField("elem", elem)
@@ -337,6 +331,9 @@
 			init = append(init, r)
 		}
 	}
+	if nsends+nrecvs != ncas {
+		Fatalf("walkselectcases: miscount: %v + %v != %v", nsends, nrecvs, ncas)
+	}
 
 	// run the select
 	lineno = sellineno
@@ -345,7 +342,7 @@
 	r = nod(OAS2, nil, nil)
 	r.List.Set2(chosen, recvOK)
 	fn := syslook("selectgo")
-	r.Rlist.Set1(mkcall1(fn, fn.Type.Results(), nil, bytePtrToIndex(selv, 0), bytePtrToIndex(order, 0), pc0, nodintconst(int64(n))))
+	r.Rlist.Set1(mkcall1(fn, fn.Type.Results(), nil, bytePtrToIndex(selv, 0), bytePtrToIndex(order, 0), pc0, nodintconst(int64(nsends)), nodintconst(int64(nrecvs)), nodbool(dflt == nil)))
 	r = typecheck(r, ctxStmt)
 	init = append(init, r)
 
@@ -357,14 +354,11 @@
 	}
 
 	// dispatch cases
-	for i, cas := range cases.Slice() {
-		setlineno(cas)
-
-		cond := nod(OEQ, chosen, nodintconst(int64(i)))
+	dispatch := func(cond, cas *Node) {
 		cond = typecheck(cond, ctxExpr)
 		cond = defaultlit(cond, nil)
 
-		r = nod(OIF, cond, nil)
+		r := nod(OIF, cond, nil)
 
 		if n := cas.Left; n != nil && n.Op == OSELRECV2 {
 			x := nod(OAS, n.List.First(), recvOK)
@@ -377,6 +371,15 @@
 		init = append(init, r)
 	}
 
+	if dflt != nil {
+		setlineno(dflt)
+		dispatch(nod(OLT, chosen, nodintconst(0)), dflt)
+	}
+	for i, cas := range casorder {
+		setlineno(cas)
+		dispatch(nod(OEQ, chosen, nodintconst(int64(i))), cas)
+	}
+
 	return init
 }
 
@@ -395,7 +398,6 @@
 		scase = tostruct([]*Node{
 			namedfield("c", types.Types[TUNSAFEPTR]),
 			namedfield("elem", types.Types[TUNSAFEPTR]),
-			namedfield("kind", types.Types[TUINT16]),
 		})
 		scase.SetNoalg(true)
 	}
diff --git a/src/reflect/all_test.go b/src/reflect/all_test.go
index ed2f225..5a12699 100644
--- a/src/reflect/all_test.go
+++ b/src/reflect/all_test.go
@@ -1725,6 +1725,14 @@
 	_, _, _ = Select(sCases)
 }
 
+func TestSelectNop(t *testing.T) {
+	// "select { default: }" should always return the default case.
+	chosen, _, _ := Select([]SelectCase{{Dir: SelectDefault}})
+	if chosen != 0 {
+		t.Fatalf("expected Select to return 0, but got %#v", chosen)
+	}
+}
+
 func BenchmarkSelect(b *testing.B) {
 	channel := make(chan int)
 	close(channel)
diff --git a/src/runtime/select.go b/src/runtime/select.go
index d7c7d9f..80768b2 100644
--- a/src/runtime/select.go
+++ b/src/runtime/select.go
@@ -12,23 +12,12 @@
 
 const debugSelect = false
 
-// scase.kind values.
-// Known to compiler.
-// Changes here must also be made in src/cmd/compile/internal/gc/select.go's walkselectcases.
-const (
-	caseNil = iota
-	caseRecv
-	caseSend
-	caseDefault
-)
-
 // Select case descriptor.
 // Known to compiler.
 // Changes here must also be made in src/cmd/internal/gc/select.go's scasetype.
 type scase struct {
 	c    *hchan         // chan
 	elem unsafe.Pointer // data element
-	kind uint16
 }
 
 var (
@@ -115,7 +104,7 @@
 // ordinal position of its respective select{recv,send,default} call.
 // Also, if the chosen scase was a receive operation, it reports whether
 // a value was received.
-func selectgo(cas0 *scase, order0 *uint16, pc0 *uintptr, ncases int) (int, bool) {
+func selectgo(cas0 *scase, order0 *uint16, pc0 *uintptr, nsends, nrecvs int, block bool) (int, bool) {
 	if debugSelect {
 		print("select: cas0=", cas0, "\n")
 	}
@@ -125,6 +114,7 @@
 	cas1 := (*[1 << 16]scase)(unsafe.Pointer(cas0))
 	order1 := (*[1 << 17]uint16)(unsafe.Pointer(order0))
 
+	ncases := nsends + nrecvs
 	scases := cas1[:ncases:ncases]
 	pollorder := order1[:ncases:ncases]
 	lockorder := order1[ncases:][:ncases:ncases]
@@ -158,16 +148,12 @@
 	// optimizing (and needing to test).
 
 	// generate permuted order
-	dfli := -1
 	norder := 0
 	for i := range scases {
 		cas := &scases[i]
 
 		// Omit cases without channels from the poll and lock orders.
 		if cas.c == nil {
-			if cas.kind == caseDefault {
-				dfli = i
-			}
 			cas.elem = nil // allow GC
 			continue
 		}
@@ -250,8 +236,7 @@
 		cas = &scases[casi]
 		c = cas.c
 
-		switch cas.kind {
-		case caseRecv:
+		if casi >= nsends {
 			sg = c.sendq.dequeue()
 			if sg != nil {
 				goto recv
@@ -262,8 +247,7 @@
 			if c.closed != 0 {
 				goto rclose
 			}
-
-		case caseSend:
+		} else {
 			if raceenabled {
 				racereadpc(c.raceaddr(), casePC(casi), chansendpc)
 			}
@@ -280,9 +264,9 @@
 		}
 	}
 
-	if dfli >= 0 {
+	if !block {
 		selunlock(scases, lockorder)
-		casi = dfli
+		casi = -1
 		goto retc
 	}
 
@@ -311,12 +295,10 @@
 		*nextp = sg
 		nextp = &sg.waitlink
 
-		switch cas.kind {
-		case caseRecv:
-			c.recvq.enqueue(sg)
-
-		case caseSend:
+		if casi < nsends {
 			c.sendq.enqueue(sg)
+		} else {
+			c.recvq.enqueue(sg)
 		}
 	}
 
@@ -359,7 +341,7 @@
 			}
 		} else {
 			c = k.c
-			if k.kind == caseSend {
+			if int(casei) < nsends {
 				c.sendq.dequeueSudoG(sglist)
 			} else {
 				c.recvq.dequeueSudoG(sglist)
@@ -378,27 +360,29 @@
 	c = cas.c
 
 	if debugSelect {
-		print("wait-return: cas0=", cas0, " c=", c, " cas=", cas, " kind=", cas.kind, "\n")
+		print("wait-return: cas0=", cas0, " c=", c, " cas=", cas, " send=", casi < nsends, "\n")
 	}
 
-	if cas.kind == caseRecv {
+	if casi < nsends {
+		if !caseSuccess {
+			goto sclose
+		}
+	} else {
 		recvOK = caseSuccess
-	} else if cas.kind == caseSend && !caseSuccess {
-		goto sclose
 	}
 
 	if raceenabled {
-		if cas.kind == caseRecv && cas.elem != nil {
-			raceWriteObjectPC(c.elemtype, cas.elem, casePC(casi), chanrecvpc)
-		} else if cas.kind == caseSend {
+		if casi < nsends {
 			raceReadObjectPC(c.elemtype, cas.elem, casePC(casi), chansendpc)
+		} else if cas.elem != nil {
+			raceWriteObjectPC(c.elemtype, cas.elem, casePC(casi), chanrecvpc)
 		}
 	}
 	if msanenabled {
-		if cas.kind == caseRecv && cas.elem != nil {
-			msanwrite(cas.elem, c.elemtype.size)
-		} else if cas.kind == caseSend {
+		if casi < nsends {
 			msanread(cas.elem, c.elemtype.size)
+		} else if cas.elem != nil {
+			msanwrite(cas.elem, c.elemtype.size)
 		}
 	}
 
@@ -526,29 +510,57 @@
 		block()
 	}
 	sel := make([]scase, len(cases))
-	order := make([]uint16, 2*len(cases))
-	for i := range cases {
-		rc := &cases[i]
+	orig := make([]int, len(cases))
+	nsends, nrecvs := 0, 0
+	dflt := -1
+	for i, rc := range cases {
+		var j int
 		switch rc.dir {
 		case selectDefault:
-			sel[i] = scase{kind: caseDefault}
+			dflt = i
+			continue
 		case selectSend:
-			sel[i] = scase{kind: caseSend, c: rc.ch, elem: rc.val}
+			j = nsends
+			nsends++
 		case selectRecv:
-			sel[i] = scase{kind: caseRecv, c: rc.ch, elem: rc.val}
+			nrecvs++
+			j = len(cases) - nrecvs
 		}
+
+		sel[j] = scase{c: rc.ch, elem: rc.val}
+		orig[j] = i
 	}
 
+	// Only a default case.
+	if nsends+nrecvs == 0 {
+		return dflt, false
+	}
+
+	// Compact sel and orig if necessary.
+	if nsends+nrecvs < len(cases) {
+		copy(sel[nsends:], sel[len(cases)-nrecvs:])
+		copy(orig[nsends:], orig[len(cases)-nrecvs:])
+	}
+
+	order := make([]uint16, 2*(nsends+nrecvs))
 	var pc0 *uintptr
 	if raceenabled {
-		pcs := make([]uintptr, len(cases))
+		pcs := make([]uintptr, nsends+nrecvs)
 		for i := range pcs {
 			selectsetpc(&pcs[i])
 		}
 		pc0 = &pcs[0]
 	}
 
-	return selectgo(&sel[0], &order[0], pc0, len(cases))
+	chosen, recvOK := selectgo(&sel[0], &order[0], pc0, nsends, nrecvs, dflt == -1)
+
+	// Translate chosen back to caller's ordering.
+	if chosen < 0 {
+		chosen = dflt
+	} else {
+		chosen = orig[chosen]
+	}
+	return chosen, recvOK
 }
 
 func (q *waitq) dequeueSudoG(sgp *sudog) {