Replace only loads matching the store type.

Replace only loads matching the store type.

If a load uses the same address as a previous store, we can only
replace it with the store's data when their types match. Also,
stores can only be eliminated when all the loads following them have
been replaced.

Bug swiftshader:48

Change-Id: I5968b256cb295243c30df3598e49015bccb5bff1
Reviewed-on: https://swiftshader-review.googlesource.com/10950
Tested-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>