cmd/compile: handle defined iter func type correctly

Fixed #64930

Change-Id: I916de7f97116fb20cb2f3f0b425ac34409afd494
Reviewed-on: https://go-review.googlesource.com/c/go/+/553436
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Auto-Submit: Cuong Manh Le <cuong.manhle.vn@gmail.com>

src/cmd/compile/internal/rangefunc/rewrite.go

@@ -934,7 +934,7 @@ func (r *rewriter) endLoop(loop *forLoop) {
 	if rfunc.Params().Len() != 1 {
 		base.Fatalf("invalid typecheck of range func")
 	}
-	ftyp := rfunc.Params().At(0).Type().(*types2.Signature) // func(...) bool
+	ftyp := types2.CoreType(rfunc.Params().At(0).Type()).(*types2.Signature) // func(...) bool
 	if ftyp.Results().Len() != 1 {
 		base.Fatalf("invalid typecheck of range func")
 	}

test/range4.go

@@ -311,6 +311,30 @@ func testcalls() {
 	}
 }
 
+type iter3YieldFunc func(int, int) bool
+
+func iter3(list ...int) func(iter3YieldFunc) {
+	return func(yield iter3YieldFunc) {
+		for k, v := range list {
+			if !yield(k, v) {
+				return
+			}
+		}
+	}
+}
+
+func testcalls1() {
+	ncalls := 0
+	for k, v := range iter3(1, 2, 3) {
+		_, _ = k, v
+		ncalls++
+	}
+	if ncalls != 3 {
+		println("wrong number of calls:", ncalls, "!= 3")
+		panic("fail")
+	}
+}
+
 func main() {
 	testfunc0()
 	testfunc1()
@@ -323,4 +347,5 @@ func main() {
 	testfunc8()
 	testfunc9()
 	testcalls()
+	testcalls1()
 }