It isn't safe, the place where we're moving the value to
might have a different live memory.  Moving will introduce
two simultaneously live memories.

Change-Id: I07e61a6db8ef285088c530dc2e5d5768d27871ff
Reviewed-on: https://go-review.googlesource.com/16099Reviewed-by: David Chase <drchase@google.com>
Run-TryBot: David Chase <drchase@google.com>