While doing the SVE ACLE work, I hit a case in which a pattern had two iterators and used an attribute without saying which iterator it was referring to. The choice of iterator made a difference and in this case the implicit choice happened to be the "wrong" one.
This series raises an error for cases in which an unprefixes attribute could expand to different things depending on the iterator chosen. It also tries to fix all instances in the ports. Bootstrapped & regression-tested on aarch64-linux-gnu and x86_64-linux-gnu. Also tested by building at least one target per CPU directory and (a) checking for errors and (b) diffing the autogenerated files before and after the patch. Richard
