Jeez, I hope it did not require “security hardening” for Nvidia to do something this basic. If these other vendors missed some tiny corner resulting in state leakage, that would be understandable. But, forgetting to clear local memory is just inexcusable.

Imagine a OS forgetting to replace your general purpose registers across context switches. Only a rank incompetent and useless security process would let something like that get all the way through to deployment.

Could probably be that the shared memory (at least in the past) also was used for cache, so the same mechanism that probably sanitizer the cache is/was in play here.

Google used AMD GPUs for Stadia, not NVIDIA.

Could imagine it being related to CUDA as well. Memory being consistently zero-initialized helps prevent application bugs.