These are the packages that would be merged, in order:

Calculating dependencies ...

!!! Problem resolving dependencies for =dev-util/hip-6.4.3-r2
 done!
Dependency resolution took 0.83 s (backtrack: 0/20).


!!! The ebuild selected to satisfy "=dev-util/hip-6.4.3-r2" has unmet requirements.
- dev-util/hip-6.4.3-r2::gentoo USE="hip -debug -doc (-opencl) -test" LLVM_SLOT="20" VIDEO_CARDS="-amdgpu -nvidia"

  The following REQUIRED_USE flag constraints are unsatisfied:
    exactly-one-of ( video_cards_amdgpu video_cards_nvidia )

  The above constraints are a subset of the following complete expression:
    any-of ( hip opencl ) exactly-one-of ( video_cards_amdgpu video_cards_nvidia ) exactly-one-of ( llvm_slot_20 )