Do not replace a live phi with a dead phi.

A dead phi is not properly typed. Therefore, always use the live phi
equivalent instead.

bug:21865466

(cherry picked from commit 4230e1895b915a22363452823b0e51eabe92cb60)

Change-Id: If9a3313fc953c2eb4be85b625676e48112fcb1f6
5 files changed