Fix register corruption and save constant pool register.

R=joransiu@ca.ibm.com, jyan@ca.ibm.com
BUG=
LOG=N

Change-Id: I278b7f9a60e10c5347cdfba52432837f68c82836
Reviewed-on: https://chromium-review.googlesource.com/649812
Commit-Queue: Junliang Yan <jyan@ca.ibm.com>
Reviewed-by: Junliang Yan <jyan@ca.ibm.com>
Cr-Commit-Position: refs/heads/master@{#47832}