There appears to have been some code leak when copying from the COPY2x8
macro above where we're reading 8 bytes into d4-d7 directly after
reading 4 bytes into s4-s7. These 32 bytes in d4-7 are unused and can
possibly overrun the boundary of allocated memory -- Valgrind detected
this which is what dragged my attention to it for a 128,1 copy.
Additionally, there is no need to update the addresses stored in A0-A7
as the only possible paths after running this macro will overwrite A0-7
if looping to the next 8 rows, or overwrite A0-3 if moving to 4 rows --
in which case A4-7 are unused.
d2bda3b56a