Port 5dfe23a4

Original Commit Message:

    When encountering a LoadStackPointer input to a comparison, generate a register
    LocationOperand that points to the stack pointer. This can avoid unnecessary
    spilling of the stack pointer.

R=georgia.kouveli@arm.com, joransiu@ca.ibm.com, michael_dawson@ca.ibm.com
BUG=
LOG=N

Change-Id: Ie3fecf70f78c234fefad86fec74820a61f3d227b
Reviewed-on: https://chromium-review.googlesource.com/1057965Reviewed-by: Joran Siu <joransiu@ca.ibm.com>
Commit-Queue: Junliang Yan <jyan@ca.ibm.com>
Cr-Commit-Position: refs/heads/master@{#53167}