Helpful for indexed loads and stores when the stride is not equal to
the size being loaded/stored.

Update #7927

Change-Id: I8714dd4c7b18a96a611bf5647ee21f753d723945
Reviewed-on: https://go-review.googlesource.com/21346
Run-TryBot: Todd Neal <todd@tneal.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Todd Neal <todd@tneal.org>