re PR tree-optimization/87914 (gcc fails to vectorize bitreverse code)

re PR tree-optimization/87914 (gcc fails to vectorize bitreverse code)

2018-11-07  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/87914
	* tree-vect-loop.c (vect_is_simple_reduction): Improve detection
	of nested cycles.
	(vectorizable_reduction): Handle shifts and rotates by dispatching
	to vectorizable_shift.
	* tree-vect-stmts.c (vect_get_vec_def_for_operand_1): Handle
	in-loop uses of vect_nested_cycle defs.  Merge cycle and internal
	def cases.
	(vectorizable_shift): Export and handle being called as
	vect_nested_cycle.
	(vect_analyze_stmt): Call vectorizable_shift after
	vectorizable_reduction.
	* tree-vectorizer.h (vectorizable_shift): Declare.

	* lib/target-supports.exp (check_effective_target_vect_var_shift): New.
	(check_avx2_available): Likewise.
	* g++.dg/vect/pr87914.cc: New testcase.

From-SVN: r265876