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Well all modern architectures have FP and SIMD so it’s not as though complex (microcoded) instructions have been banished.
by klelatti 3y ago
Well all modern architectures have FP and SIMD so it’s not as though complex (microcoded) instructions have been banished.
- atq2119 3y agoSIMD instructions are generally not microcoded though because they are not actually complex. A SIMD addition has pretty much the same microarchitectural complexity as a scalar addition. If you're looking for truly complex instructions, you should look for things like VMENTER or IRET.
- stephencanon 3y agoMost SIMD and FP instructions are not microcoded in a modern mainstream CPU, FWIW.
- klelatti 3y agoInteresting. I sort of expected that for basic FP / SIMD but not for the full range - eg trig functions. Is that wrong?
- stephencanon 3y agoThere really aren't complex math functions in most SIMD ISAs(1), these functions are implemented in software instead. Even for scalar operations, no one(2) uses the x87 trig functions either, as software implementations are both faster and more accurate and have been for a couple decades. (1) various HPC folks have proposed and used extensions that do _part_ of a complex math operation in SIMD at various times, and on GPUs this sort of thing is very common. (2) except for math libraries that haven't been updated for a couple decades.
- deleted 3y ago[deleted]
- rerdavies 3y ago@klelatti As far as I know, nobody has SIMD trig functions at the instruction level. FP trig functions are definitely micro-coded, and are (as-far-as-I-know) found only on CISC processors. (HN seems to have a limit on how deeply you can nest replies. I can't reply to @klelatti's post direct :-/ )