Performance of INHERIT-META

I did a little bit of performance sampling and noticed a fair bit of boot time was spent in a function called INHERIT-META. It's was called often, and it was slow.

Carl & BrianH & co were big fans of taking bottleneck functions and making them natives. I've tried to avoid that for "weird" functions, but I will make an exception here.

I'm keeping a copy of the original code, which isn't even complete...despite being slow. :-/

inherit-meta: func* [
    return: "Same as derived (assists in efficient chaining)"
    derived [action!]
    original "Passed as WORD! to use GET to avoid tainting cached label"
    /augment "Additional spec information to scan"
    original: get original  ; GET so `specialize :foo [...]` keeps label foo

    if let m1: meta-of :original [
        set-meta :derived let m2: copy :m1  ; shallow copy
        if select m1 'parameter-notes [  ; shallow copy, but make frame match
            m2/parameter-notes: make frame! :derived
            for-each [key value] m1/parameter-notes [
                if in m2/parameter-notes key [
                    m2/parameter-notes/(key): get* 'value  ; !!! BAD-WORD!s
        if select m1 'parameter-types [  ; shallow copy, but make frame match
            m2/parameter-types: make frame! :derived
            for-each [key value] m1/parameter-types [
                if in m2/parameter-types key [
                    m2/parameter-types/(key): get* 'value  ; !!! BAD-WORD!s
    return get 'derived  ; no :derived name cache

Main point is, what is it supposed to do?