Yes and it's slightly different per architecture. Mostly new instructions (like the discussed one in this article).

Just RDNA4 ISA and you'll find it:https://www.amd.com/content/dam/amd/en/documents/radeon-tech...

Terrascale from 2008 was very different. Ignore it.

GCN is mostly the same as RDNA and GCN is practically identical to CDNA. So you can go back to older guides as far back as GCN1 (like early 2010s era). The only fundamental difference is RDNA is SIMD32 while GCN/CDNA is SIMD64

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NVidia has an intermediate assembly language called PTX. NVidias true assembly language is undocumented (but not secret, not just intended for general purpose coding). Search on NVidias PTX manual and you'll see ...