2012-01-04  Richard Guenther  <rguenther@suse.de>

	PR middle-end/51750
	* tree.c (size_low_cst): New function.
	* tree.h (size_low_cst): Declare.
	* fold-const.c (fold_comparison): Use it to extract the low
	part of the POINTER_PLUS_EXPR offset.

From-SVN: r182872