Which compilers would support it, which assemblers would? Does it enable any "killer features"?
Matt Hey has been ready for years now, with 1 or more assemblers revved up and ready to go as soon as Gunnar publishes the official bitmap list of all the instructions.
Instead of adding a series of seemingly nice, but in reality almost useless low-level additions, it would be much more sensible to add higher level functionalities that enable new killer features the Amiga did not have originally, and from which multiple programs could benefit. Say, JPEG decoding or MP3 decoding. None of the new instructions make these tasks simpler, easier or faster - they are too low-level. What it would probably take would be a hardware engine for some of the components of these standards (Huffman decoder, DCT, digital filters... hence, multiply-add instructions, shift-and-mask instructions and so on).
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I know, there is the cycle counter party whose members would sell their grandma to reduce the number of clock cycles in a totally uninteresting part of a program, and maybe you want to address the demand from those folks. However, beware! The outcome of such activitly is usually less useful than one may hope for, leave alone the stability, and the increased performance is usually not what you have hoped for.
The 2 main ways to speed up a program are A) cycle-counting to cycle-optimize things and B) rewriting the algorithm from the ground up to be more efficient.
We are not allowed to rewrite the mp3 algorithm or the jpeg algorithm or the h264 algorithm or the h265 algorithm. So the ONLY thing we can do to speed up our software right now is to do the cycle-counting tricks. The best way is to add new instructions to the ISA.
All the asm coders on the Natami forum asked for "Multiply-add with clipping" instruction(s) because they allow a dramatic speed increase for audio and video codecs. Iirc it applies to jpeg decoding also.
Does the Apollo Core have a MADD instruction? When I left off years ago, Gunnar wasn't allowing it. But maybe he changed his mind now? I asked to read the instruction manual to find out but Gunnar hasn't provided it yet.
Sadly without a list of the new instructions, and their bitpatterns (sometimes referred to as opcodes) I can't go around saying how great the new ISA is when I don't even know
what it is.