fp_usability

    const fp_usability: FpUsability = switch (builtin.target.cpu.arch) {
        .alpha,
        .avr,
        .csky,
        .microblaze,
        .microblazeel,
        .mips,
        .mipsel,
        .mips64,
        .mips64el,
        .msp430,
        .sh,
        .sheb,
        .xcore,
        .xtensa,
        .xtensaeb,
        => .useless,
        .hexagon,
        // The PowerPC ABIs don't actually strictly require a backchain pointer; they allow omitting
        // it when full unwind info is present. Despite this, both GCC and Clang always enforce the
        // presence of the backchain pointer no matter what options they are given. This seems to be
        // a case of "the spec is only a polite suggestion", except it works in our favor this time!
        .powerpc,
        .powerpcle,
        .powerpc64,
        .powerpc64le,
        .sparc,
        .sparc64,
        => .ideal,
        // https://developer.apple.com/documentation/xcode/writing-arm64-code-for-apple-platforms#Respect-the-purpose-of-specific-CPU-registers
        .aarch64 => if (builtin.target.os.tag.isDarwin()) .safe else .unsafe,
        else => .unsafe,
    }