OK! for anyone coming across this issue: I solved the issue by adding NVPTX to LLVM_TARGETS Extended USE flag inside /etc/portage/make.conf.
On my previous installation, I had this Extended USE flag enabled. But, I thought it was unnecessary. OK, what does it do?
It is being used by Mesa for I guess building shaders or something like that, though I am not sure what’s the exact usage; so I had to:
Change:
LLVM_TARGETS="BPF X86"
To:
LLVM_TARGETS="BPF NVPTX X86"
And:
$ emerge -a --oneshot `equery depends llvm|awk '{print " ="$1}'`
These are the packages that would be merged, in order:
Calculating dependencies... done!
[ebuild R ] sys-devel/llvm-7.0.0-r1
[ebuild R ] sys-devel/llvmgold-7
[ebuild R ] sys-libs/libcxxabi-7.0.0
[ebuild R ] sys-devel/lld-7.0.0
[ebuild R ] sys-libs/libcxx-7.0.0
[ebuild R ] sys-devel/clang-7.0.0
[ebuild R ] media-libs/mesa-18.2.4
[ebuild R ] sys-libs/compiler-rt-7.0.0
[ebuild R ] dev-util/lldb-7.0.0
[ebuild R ] sys-libs/compiler-rt-sanitizers-7.0.0
[ebuild R ] www-client/firefox-64.0
Would you like to merge these packages? [Yes/No]
Did a reboot and now I’m getting 120 FPS on -vulkan 