I acquired a copy of the Itanium manuals, and in flicking through it, you can barely get through a page before going "you did WHAT?" over some feature.

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tptacek 5 hours ago | parent [-]

Example example example example must see examples!

	▲	jcranmer an hour ago \| parent [-]
		Some of the examples: * Itanium has register windows. * Itanium has register rotations, so that you can modulo-schedule a loop. * Itanium has so many registers that a context switch is going to involve spilling several KB of memory. * The main registers have "Not-a-Thing" values to be able to handle things like speculative loads that would have trapped. Handling this for register spills (or context switches!) appears to be "fun." * It's a bi-endian architecture. * The way you pack instructions in the EPIC encoding is... fun. * The rules of how you can execute instructions mean that you kind of have branch delay slots, but not really. * There are four floating-point environments because why not. * Also, Itanium is predicated. * The hints, oh god the hints. It feels like every time someone came up with an idea for a hint that might be useful to the processor, it was thrown in there. How is a compiler supposed to be able to generate all of these hints? * It's an architecture that's complicated enough that you need to handwrite assembly to get good performance, but the assembly has enough arcane rules that handwriting assembly is unnecessarily difficult.