per-system-optim/default.nix

{
  nixpkgs ? <nixpkgs>,
  nixpkgs-unpatched ? null,
  system ? builtins.currentSystem,
}: let
  nixpkgs-unpatched' =
    if nixpkgs-unpatched == null
    then nixpkgs
    else nixpkgs-unpatched;
  localSystems = rec {
    x86_64-linux.system = "x86_64-linux";
    aarch64-linux.system = "aarch64-linux";
    default.system = system;
    skylake =
      x86_64-linux
      // {
        gcc.arch = "skylake";
        gcc.tune = "skylake";
      };
    skylake-avx512 = skylake; # Currently none of my builders support avx512. Revisit when upgraded to znver4
    neoverse-n1 =
      aarch64-linux
      // {
        gcc.arch = "armv8.2-a";
        gcc.tune = "neoverse-n1";
      };
    znver1 =
      x86_64-linux
      // {
        gcc.arch = "znver1";
        gcc.tune = "znver1";
      };
    znver2 =
      x86_64-linux
      // {
        gcc.arch = "znver2";
        gcc.tune = "znver2";
      };
  };
  pkgs-unpatched = import nixpkgs-unpatched' {
    inherit system;
    overlays = [
      (_: _: {
        nixpkgs-unpatched = nixpkgs-unpatched';
      })
      (import ./overlay.nix)
    ];
    config.contentAddressedByDefault = true;
  };
  pkgsFor = system: args:
    import nixpkgs (args
      // {
        localSystem = localSystems.${system};
        overlays = [
          (_: _: {
            nixpkgs-unpatched = nixpkgs-unpatched';
          })
          (import ./overlay.nix)
        ];
      });
  keepBuilt = system: let
    pkgs = pkgsFor system {};
  in {
    inherit (pkgs) nixos-rebuild;
  };
in {
  inherit (pkgs-unpatched) nixpkgs;
  inherit pkgsFor;
  x86_64-linux = keepBuilt "x86_64-linux";
  aarch64-linux = keepBuilt "aarch64-linux";
  default = keepBuilt "default";
  skylake = keepBuilt "skylake";
  skylake-avx512 = keepBuilt "skylake-avx512";
  neoverse-n1 = keepBuilt "neoverse-n1";
  znver1 = keepBuilt "znver1";
  znver2 = keepBuilt "znver2";
}