orderstmt's OSELECT case reuses t as a temporary *NodeList even though it's still live and used for the poptemp call later:

func orderstmt(n *Node, order *Order) {
    ...
    switch n.Op {
    ...
    case OSELECT:
        t := marktemp(order)
        ...
                case OSELRECV, OSELRECV2:
                    if r.Colas {
                        t = r.Ninit
        ...
        poptemp(t, order)
    ...
}

In practice, this currently seems to work out okay because we don't allow inlining of functions with select statements, so marktemp(order) will always return nil, and the r.Colas branch will set t back to nil (or else we'll hit the Yyerror("ninit on select recv") error and fail anyway).

If I comment out OSELECT in inl.go:ishairy, then I notice this program causes marktemp(order) to return non-nil but then t is changed to nil before the poptemp(t, order) call:

package repro

func f() int
func g(int, int) int
func h(ch chan int) int {
    select {
    case x := <-ch:
        return x
    }
}

func repro() {
    g(f(), h(nil))
}