poly_int: expand_debug_expr

poly_int: expand_debug_expr

This patch makes expand_debug_expr track polynomial memory offsets.
It simplifies the handling of the case in which the reference is not
to the first byte of the base, which seemed non-trivial enough to
make it worth splitting out as a separate patch.

2017-12-20  Richard Sandiford  <richard.sandiford@linaro.org>
	    Alan Hayward  <alan.hayward@arm.com>
	    David Sherwood  <david.sherwood@arm.com>

gcc/
	* tree.h (get_inner_reference): Add a version that returns the
	offset and size as poly_int64_pods rather than HOST_WIDE_INTs.
	* cfgexpand.c (expand_debug_expr): Track polynomial offsets.  Simply
	the case in which bitpos is not associated with the first byte.

Co-Authored-By: Alan Hayward <alan.hayward@arm.com>
Co-Authored-By: David Sherwood <david.sherwood@arm.com>
From-SVN: r255892