The following checkdead message is false positive:

$ go test -race -c runtime
$ ./runtime.test -test.cpu=2 -test.run=TestSmhasherWindowed -test.v
=== RUN TestSmhasherWindowed-2
checkdead: find g 18 in status 1
SIGABRT: abort
PC=0x42bff1

LGTM=rsc
R=golang-codereviews, gobot, rsc
CC=golang-codereviews, iant, khr
https://golang.org/cl/59490046