[llvm] [mlir] [mlir][gpu] Change GPU modules to globals (PR #135478)

[Mehdi Amini via llvm-commits]

joker-eph wrote:

Would it be possible to lazy load on first use? 
Right now this would all happen eagerly on application startup, and consume GPU memory even for kernels that wouldn't be used (If I understand correctly the change)

https://github.com/llvm/llvm-project/pull/135478