[dragontamer]

ROCm was clearly designed with Wave64 in mind. It was going to take years for ROCm to be reworked for Wave32 of RDNA.

DirectX shaders however were already ready for Wave32, and other architectural changes that RDNA had. In fact, RDNA was basically AMD changing their architecture to be more "NVidia-like" on many regards (32-wide execute being the most noticeable).

CDNA existed because HPC has $Billion+ contracts with code written for Wave64 and still needing ROCm support. That means staying on the older GCN-like architecture and continuing to support say, DPP instructions or other obscure features of GCN.

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Remember how long it took for RDNA to get ROCm support? Did you want to screw the HPC customers for that whole time?

Splitting the two architectures, focusing ROCm on HPC (where the money was in 2018 for GPU Compute research dollars), and focusing on better video game performance for RDNA (where money is for video game / consumer cards) just makes sense.