be re-ordered according to the indices in the Swizzle format.
Like the Predication Table, it is an indirect lookup: use of a
source or destination register in any given operation, if that register
-occurs in the table, "activates" swizzling for that register.
-Note that the target is taken from the "Register Table" (regidx).
+occurs in the table, "activates" sub-vector element swizzling for
+that register. Note that the target is taken from the "Register Table"
+(regidx).
Source vectors are free to have the swizzle indices point to the same
sub-vector element. However when using swizzling on destination vectors,