https://www.jwhitham.org/2016/02/risc-instruction-sets-i-hav...
Itanium was the really odd one — it not only used register windows but could offload some of the prior windows onto the heap. Most people would probably never notice… unless you’re trying to get a conservative scanning GC working and are stumped why values in some registers seem to not be traced…
'Anyway this chip architect guy is standing up in front of this group promising the moon and stars. And I finally put my hand up and said I just could not see how you're proposing to get to those kind of performance levels. And he said well we've got a simulation, and I thought Ah, ok. That shut me up for a little bit, but then something occurred to me and I interrupted him again. I said, wait I am sorry to derail this meeting. But how would you use a simulator if you don't have a compiler? He said, well that's true we don't have a compiler yet, so I hand assembled my simulations. I asked "How did you do thousands of line of code that way?" He said “No, I did 30 lines of code”. Flabbergasted, I said, "You're predicting the entire future of this architecture on 30 lines of hand generated code?" [chuckle], I said it just like that, I did not mean to be insulting but I was just thunderstruck. Andy Grove piped up and said "we are not here right now to reconsider the future of this effort, so let’s move on".'
Like if you tried to debug a software crash on Itanium. The customer provided core dump was useless as you could not see what was going on. Intel added a debug mode to their compilers which disabled all that EPIC so hopefully you could reproduce the crash there, or on other CPU architectures. Otherwise you were basically screwed.
