poly_int: adjust_mems

poly_int: adjust_mems

This patch makes the var-tracking.c handling of autoinc addresses
cope with polynomial mode sizes.

2018-01-03  Richard Sandiford  <richard.sandiford@linaro.org>
	    Alan Hayward  <alan.hayward@arm.com>
	    David Sherwood  <david.sherwood@arm.com>

gcc/
	* var-tracking.c (adjust_mems): Treat mode sizes as polynomial.
	Use plus_constant instead of gen_rtx_PLUS.

Co-Authored-By: Alan Hayward <alan.hayward@arm.com>
Co-Authored-By: David Sherwood <david.sherwood@arm.com>
From-SVN: r256156