Need to zero/sign-ext input register before comparison

R=joransiu@ca.ibm.com

Change-Id: I3e2909d76d54c6ad5ae55114d0c501615f89184a
Reviewed-on: https://chromium-review.googlesource.com/c/1430620Reviewed-by: Joran Siu <joransiu@ca.ibm.com>
Commit-Queue: Junliang Yan <jyan@ca.ibm.com>
Cr-Commit-Position: refs/heads/master@{#59047}