Gentoo LLVM_TARGETS not Working?

Recently, I would like to test switching from gcc to clang on my Gentoo VM. Because if so, I can install Rust and Zig from source without worrying about adding the HUGE clang dependency that won't be used by other packages. Later I will remove gcc :)

problem

First I want to make LLVM not targeting too many platform, but changing LLVM_TARGETS don't work

  [ebuild  N     ] sys-devel/llvm-15.0.3:15::gentoo  USE="binutils-plugin libffi
  ncurses -debug -doc -exegesis -libedit -test -verify-sig -xar -xml -z3 -zstd"
  LLVM_TARGETS="(AArch64) (AMDGPU) (ARM) (AVR) (BPF) (Hexagon) (Lanai) (MSP430)
  (Mips) (NVPTX) (PowerPC) (RISCV) (Sparc) (SystemZ) (VE) (WebAssembly) (X86)
  (XCore) (-ARC) (-CSKY) (-DirectX) (-LoongArch) (-M68k) (-SPIRV)" 241 KiB

and I found [solved] LLVM_TARGETS not respected?(Mar 2022) on gentoo forum

It seems that global LLVM_TARGETS setting is not respected, and flags such as llvm_targets_AArch64, llvm_targets_ARM, are no longer there. They're now forced by default as a precaution.

solution

add something like `/ -llvm_targets_AArch64` into `/etc/portage/profile/package.use.force`

I excluded all targets exept for X86, but still 3 left: AMDGPU, BPF, NVPTX

so I also add `sys-devel/llvm -llvm_targets_AMDGPU -llvm_targets_BPF -llvm_targets_NVPTX` in `/etc/portage/package.use/`

and don't forget to add that three excluder to clang or other compiler that uses llvm

finally I got this:

  [ebuild  N     ] sys-devel/llvm-15.0.3:15::gentoo  USE="binutils-plugin libffi
  ncurses -debug -doc -exegesis -libedit -test -verify-sig -xar -xml -z3 -zstd"
  LLVM_TARGETS="(X86) -AArch64 -AMDGPU (-ARC) -ARM -AVR -BPF (-CSKY) (-DirectX)
  -Hexagon -Lanai (-LoongArch) (-M68k) -MSP430 -Mips -NVPTX -PowerPC -RISCV
  (-SPIRV) -Sparc -SystemZ -VE -WebAssembly -XCore" 241 KiB

in the end, Gentoo cheatsheet and Gentoo Wiki: Clang could be useful.

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