[PATCH PR66449]Fix ICE by using POINTER_PLUS_EXPR for pointers.

[Bin Cheng]

Hi,
This patch fixes ICE in PR66449 by using POINTER_PLUS_EXPR for pointers.
Bootstrap and test on x86_64.  Is it OK trunk?

Thanks,
bin

2015-06-18  Bin Cheng  <bin.ch...@arm.com>

        PR tree-optimization/66449
        * tree-ssa-loop-niter.c (loop_exits_before_overflow): Use
        POINTER_PLUS_EXPR for pointers.

gcc/testsuite/ChangeLog
2015-06-18  Bin Cheng  <bin.ch...@arm.com>

        PR tree-optimization/66449
        * gcc.dg/vect/pr66449.c: New.