http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21855
--- Comment #17 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-01-10 16:30:30 UTC --- (In reply to comment #16) > (In reply to comment #15) > > (In reply to comment #14) > > > (In reply to comment #13) > > > > We can't optimize this because System.out.println can change args[]. > > > > > > That's the whole point: System.out.println cannot change args[], which is > > > a > > > java array, and the length of a Java array is constant. It is not an > > > invalid > > > test case. > > > > I suppose > > > > public static void main(String[] args) > > > > is passing args by value (but the implementation detail uses reference > > passing for efficiency?). > > args is indeed a reference to a Java array. The length field of a Java > array is immutable. The elements of an array are not immutable. You mean that System.out.println could change the elements of the array (well, it doesn't, but theoretically it could)? > > In this case the Java frontend should do > > like the C++ frontend and tell this to the middle-end by properly > > marking args as 1) DECL_BY_REFERENCE, 2) use a TYPE_RESTRICT qualified > > pointer for the reference. Then we would optimize this case. > > If we could mark the length field as immutable that would fix it. Is there > any > way to do that? No. What you can do is, via the method I outlined, tell GCC that args is to be treated similar to a local automatic variable - thus it cannot be refered to from other functions (unless you pass them its address of course).
