Our late but not lamented HP Windows PC has died (drive failure caused by bad system thermal design), so I've decided to replace it with two machines, neither from HP. This evening I bought the first replacement -- a 1.4 GHz Mac Mini (the other will be a Dell). I've installed OpenMCL already, am downloading Xcode, and plan to begin testing it (and CMUCL, and SBCL) tomorrow.
I wrote a random type propagation tester for lisp compilers and have been extending it to more and more lisp types. Good type propagation is important for efficiently compiling Common Lisp, so testing it thoroughly is also important.
In a nutshell, this tester does differential testing between direct calls to an operator and calls that are embedded in a form with various inlined constants and with various type declarations. It found lots of problems with integer optimizations in gcl, problems with complexes and BIT-* functions in SBCL, a bizarre bug in Allegro CL's integer square root function, and many other bugs in various implementations.