Mentor Precision & illegal altclockctrl inferring

Good luck

The word I got from the Synopsys Sales Guys (I know its not mentor, but):

"Xilinx are very open about letting 3rd parties write tools for them, and will admit that 3rd party tools are much better

Altera are very closed to 3rd parties, and we cannot do better than their own Synthesis. I wouldnt bother buying Synplify if all you do is altera"

So Im afraid you're stuck. If precision is the only option, I suggest you raise a bug report with them.