cmd/compile: wrong liveness map

[randall77]

func f(p, q *int) (r *int) {
	r = p
	defer func() {
		recover()
	}()
	g()
	r = q
	return
}
func g()

At the call to g, r should be marked as live. It isn't.

> go tool compile -live ~/go/tmp3.go
tmp3.go:3: live at entry to f: p q
tmp3.go:7: live at call to deferproc: q r
tmp3.go:8: live at call to g: q                   <- r is live here
tmp3.go:10: live at call to deferreturn: r
tmp3.go:7: live at call to deferreturn: r

Any defer makes all of the output args live at any (possibly panicing) call.
Found using the dead-slot clobberer, https://go-review.googlesource.com/c/23924/
Seems to be around for a while, at least 1.6.
I'm not sure why the dead-slot clobberer didn't find this before.

(Note to self: original detection from encoding/gob/encoder_test.go:encodeAndRecover.)

[randall77]

@aclements

[gopherbot]

CL https://golang.org/cl/36030 mentions this issue.

[gopherbot]

CL https://golang.org/cl/23924 mentions this issue.

[gopherbot]

CL https://golang.org/cl/38133 mentions this issue.