re PR tree-optimization/87985 (Compile-time and memory hog w/ -O1 -ftree-slp-vectorize)

2018-11-14  Richard Biener  <rguenther@suse.de>

	PR middle-end/87985
	* tree-data-ref.c (split_constant_offset): Add wrapper
	allocating a cache hash-map.
	(split_constant_offset_1): Cache results of expanding
	expressions from SSA def stmts.

	* gcc.dg/pr87985.c: New testcase.

From-SVN: r266147