re PR tree-optimization/81053 (ICE on valid code at -O3 on x86_64-linux-gnu: in as_a, at is-a.h:192)

2017-06-12  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/81053
	* tree-vect-loop.c (vect_is_simple_reduction): Handle PHI
	with backedge value not defined in loop.  Simplify def stmt
	compute.

	* gcc.dg/torture/pr81053.c: New testcase.

From-SVN: r249113