The compiler is crashing on the following code:

type TypeID int
func (t *TypeID) encodeType(x int) (tt TypeID, err error) {
        switch x {
        case 0:
                return t.encodeType(x * x)
        }
        return 0, nil
}
The pass marks "return struct" {tt TypeID, err error} as used,
and this causes internal check failure.
I've added the test to:
https://golang.org/cl/6525052/diff/7020/src/pkg/runtime/race/regression_test.go

R=golang-dev, minux.ma, rsc
CC=golang-dev
https://golang.org/cl/6611049