I had to debug a problem in our program where MMX register would get corrupted under a new sampling profiler. Turns out profiler would forget to restore MMX reg

I had to debug a problem in our program where MMX register would get corrupted under a new sampling profiler. Turns out profiler would forget to restore MMX registers - the profiler devs never used MMX and it did not occur to them that a component they called would do that. That took a while to debug. Another fun bug was when alpha version of CLR failed to restore one of the two registers used to control loop execution on the Itanium. (Yes, Ia64 had two registers - one for loop variable as seen by the program and one to actually control the loop execution).