Re: C++ Garbage Collecter

[Jeffrey A Law <law@cygnus.com>]

  In message <m2btbw30qj.fsf@magnus.bothner.com>you write:
  > I don't think these statements are very relevant.  Yes, the compiler
  > sometimes does such re-writing, but that is not a problem for a 
conservative
  > collectors as long as there is still a pointer somewhere that points to
  > the actual base of the object.  And either you have a newly allocated
  > object that will be passed to someone, or it was an existing object
  > that was passed from somewhere (as an argument).  In either case, you
  > would have a pointer to the base object somewhere.
But this is precisely the problem.  You allocate a hunk of memory and initially
assign it to some variable.  Let's call it "a".

You then do a lot of indexing off "a" in a loop.  The compiler may create a
pointer outside of "a" and kill the pseudo which originally contained "a".

If you do garbage collection you lose.

ie, the compiler effectively does something like this:

  a = malloc (100)
  a -= 10
  for ( ... )
    a[10 + i] = whatever


even though you wrote

  a = malloc (100)
  for ( ...)
   a[i] = whatever



jeff