cmd/compile: mark anonymous receiver parameters as non-escaping

This was already done for normal parameters, and the same logic
applies for receiver parameters too.

Updates #24305.

Change-Id: Ia2a46f68d14e8fb62004ff0da1db0f065a95a1b7
Reviewed-on: https://go-review.googlesource.com/99335
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/compile/internal/gc/esc.go

@@ -2259,7 +2259,8 @@ func (e *EscState) esctag(fn *Node) {
 	// Unnamed parameters are unused and therefore do not escape.
 	// (Unnamed parameters are not in the Dcl list in the loop above
 	// so we need to mark them separately.)
-	for _, f := range fn.Type.Params().Fields().Slice() {
+	for _, fs := range types.RecvsParams {
+		for _, f := range fs(fn.Type).Fields().Slice() {
 			if !types.Haspointers(f.Type) { // don't bother tagging for scalars
 				continue
 			}
@@ -2271,4 +2272,5 @@ func (e *EscState) esctag(fn *Node) {
 				f.Note = mktag(EscNone)
 			}
 		}
+	}
 }

src/cmd/compile/internal/types/type.go

@@ -726,6 +726,11 @@ var RecvsParamsResults = [3]func(*Type) *Type{
 	(*Type).Recvs, (*Type).Params, (*Type).Results,
 }
 
+// RecvsParams is like RecvsParamsResults, but omits result parameters.
+var RecvsParams = [2]func(*Type) *Type{
+	(*Type).Recvs, (*Type).Params,
+}
+
 // ParamsResults is like RecvsParamsResults, but omits receiver parameters.
 var ParamsResults = [2]func(*Type) *Type{
 	(*Type).Params, (*Type).Results,

test/escape5.go

@@ -163,3 +163,15 @@ func f13() {
 	f12(&x)               // ERROR "&x does not escape"
 	runtime.KeepAlive(&x) // ERROR "&x does not escape"
 }
+
+// Test for issue 24305 (passing to unnamed receivers does not escape).
+type U int
+
+func (*U) M()   {}
+func (_ *U) N() {}
+
+func _() {
+	var u U
+	u.M() // ERROR "u does not escape"
+	u.N() // ERROR "u does not escape"
+}