cmd/compile: internal compiler error: plain block b3 len(Succs)==2, want 1 (original) (raw)

on dev.ssa branch
go version devel +be2a3e2 Thu Jul 2 08:29:33 2015 +0000 linux/amd64

compile crashes on the following program:

package a func f_ssa(){::}

go.go:2: internal compiler error: plain block b3 len(Succs)==2, want 1