Re: any? use cases. While dramatic speedup is not too common, MyHDL, a hardware description and verification language written in Python, is known to run 10 times faster on PyPy.
I also remark that MyHDL's simulation is competitive (on PyPy) with open source Icarus Verilog, in case you wonder why would anyone write HDL in Python.
http://www.myhdl.org/doku.php/performance
I also remark that MyHDL's simulation is competitive (on PyPy) with open source Icarus Verilog, in case you wonder why would anyone write HDL in Python.