Compiled regexp?

[Bastien]

After Christopher submitted a patch for org-mode, Carsten and him
discussed the difference between these two patterns:

  ;; Concat in defconst
  (defconst my-pattern (concat "^" "xyz"))
  (re-search-forward my-pattern ...)

  ;; Concat in re-search-forward
  (defconst my-partial-pattern "xyz")
  (re-search-forward (concat "^" my-partial-pattern) ...)

Both Carsten and I thought there was some optimization done
by Emacs so that the first pattern is more efficient than the
second one.  (concat "^" "xyz") would be "cached", not eval'ed
each time you search for my-pattern.

Christopher pointed to compiled_pattern in the C part of Emacs,
suggesting that there would be no difference between the two
in terms of performance.

Can anyone confirm this is the case?

Thanks,

-- 
 Bastien