[llvm] [Offload][AMDGPU] Correctly handle variable implicit argument sizes (PR #142199)

[Joseph Huber via llvm-commits]

jhuber6 wrote:

> Hold on, what "optimisation" is changing this struct? It's exposed in the ABI, in the literal sense, so LLVM really should not be hacking around with it.

You can observe it w/ optimizations and checking the notes, @arsenm would probably know explicitly where it is. It's probably find as long as the runtime is aware of this since it reports the actual size of the struct which lets you know how much of the implicit args it's using.

https://github.com/llvm/llvm-project/pull/142199