Question on remapping keys

[Drew Adams]

I have a minor mode that redefines some of the minibuffer keymaps (e.g.
minibuffer-local-completion-map). I want turning on the mode to implement
the new minibuffer bindings, and turning it off to restore the minibuffer
bindings of vanilla Emacs.

In some cases, I reuse key sequences that are bound in the global map,
binding them to other commands in minibuffer maps. Those are the bindings
that I have a question about.

In Emacs 20, I simply do this:

(substitute-key-definition from to
   minibuffer-local-completion-map global-map)

For example, to bind `C-h' in the minibuffer to command `my-help':

(substitute-key-definition 'help-command 'my-help
   minibuffer-local-completion-map global-map)

I do the same for `self-insert-command', replacing it with `my-self-insert'
for minibuffer maps.

This is very fast in Emacs 20, but in Emacs 22 it is unbearably slow. It
takes about 5 seconds for 10 such key-definition substitutions! I think that
the slowness might be due, in particular, to dealing with the case of
`self-insert-command'.

Someone suggested that I could use `define-key' with [remap...] instead of
`substitute-key-definition'. I'm not sure how to do that, since I use the
OLDMAP arg to `substitute-key-definition'. I tried using the following when
my minor mode is turned on:

(defun my-remap (from to map)
 "Remap command FROM to command TO in keymap MAP."
 (if (boundp 'this-original-command)
     (define-key map [remap `,from] to)                 ; Emacs 22
   (substitute-key-definition from to map global-map))) ; Emacs 20

And similarly when it is turned off, using nil for TO, to remove the binding
from MAP (a minibuffer map).

However, as you can guess, that doesn't work. I haven't expressed that I
want to pick up the `global-map' binding (equivalent of OLDMAP arg to
`substitute-key-definition').

Anyone have a suggestion on how to proceed? What I'm looking for is a fast
way to do more or less what (substitute-key-definition from to map
global-map) does. The performance penalty for using
`substitute-key-definition' is just too big - I need to find something
faster. Any advice would be appreciated.