having to pre-subtract an offset before running the loop.
For `sv.lfdup`, RA is Scalar so continuously accumulates
-additions of the immediate (8):
-the last write to RA is the address for
+additions of the immediate (8) but only *after* RA has been used
+as the Effective Address.
+The last write to RA is the address for
the next block (the next time round the CTR loop).
To understand this it is necessary to appreciate that
SVP64 is as if a sequence of loop-unrolled scalar instructions were