[llvm] [AMDGPU] Prevent SDWA 'preserve' transformation for instructions in different basic blocks. (PR #82406)

[Jay Foad via llvm-commits]

jayfoad wrote:

> > Why not allow the optimization, and just fix the "Move MI before v_or_b32" code in `convertToSDWA`?
> 
> I'm not sure it's safe to move instructions across possible execmask change.

I think it should be fine. This happens before control flow lowering, so exec mask changes are not explicit in the MIR anyway.

https://github.com/llvm/llvm-project/pull/82406