Optimize assume(...) away? (agaiin)

[Dmitry Antipov]

1) http://lists.gnu.org/archive/html/emacs-devel/2013-10/msg00238.html
2) http://debbugs.gnu.org/cgi/bugreport.cgi?bug=15565

3) Consider non-trivial eassert like:

eassert ((BUFFERP (it->object)
          && IT_CHARPOS (*it) == it->bidi_it.charpos
          && IT_BYTEPOS (*it) == it->bidi_it.bytepos)
         || (STRINGP (it->object)
             && IT_STRING_CHARPOS (*it) == it->bidi_it.charpos
             && IT_STRING_BYTEPOS (*it) == it->bidi_it.bytepos)
         || (CONSP (it->object) && it->method == GET_FROM_STRETCH))

  a) It takes some time to check whether there are side effects here;
  b) If someone change 'struct it' so IT_STRING_CHARPOS (*it)
     becomes a non-trivial function with side effects, it would be
     too annoying (and error-prone) to review all easserts.

Due to 1), 2) and 3) I strongly suggests to redesign eassert
to avoid any assumptions about its argument expression.

Dmitry