in memory, and critically relies on y overwrite. x is post-incremented
when read, but y is post-incremented on write. Element-Strided
ensures the Immediate (8) results in a contiguous LD (or store)
-despite RA being marked Scalar (without* modifying RA, on `sv.lfd/els`).
+despite RA being marked Scalar (*without* modifying RA, on `sv.lfd/els`).
For `sv.lfdup`, RA is Scalar so that only one
LD/ST Update "wins": the last write to RA is the address for
the next block.