[Bug java/21855] array bounds checking elimination

["aph at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21855

--- Comment #22 from Andrew Haley <aph at gcc dot gnu.org> 2012-01-10 17:08:30 UTC ---
(In reply to comment #21)
> The Java frontend could handle this by performing loads of the length field
> via a SAVE_EXPR and sharing this across a function.  That way CSE would
> happen automagically.

Now that's a nice idea.  

In this specific case it should be easy, because array.length is used in the
control expression for the loop.  So. we can create the SAVE_EXPR when the loop
is initialized.

The problem with doing this in general is that we don't have a CFG, so we don't
always know when to create that SAVE_EXPR.  If we can find an initial use of an
array that dominates all other uses we can create the SAVE_EXPR at that point.