re PR testsuite/91821 (r275928 breaks gcc.target/powerpc/sad-vectorize-2.c)

re PR testsuite/91821 (r275928 breaks gcc.target/powerpc/sad-vectorize-2.c)

2019-09-20  Richard Biener  <rguenther@suse.de>

	PR tree-optimization/91821
	* tree-vect-loop.c (check_reduction_path): Check we can compute
	reduc_idx.
	(vect_is_simple_reduction): Set STMT_VINFO_REDUC_IDX.
	* tree-vect-patterns.c (vect_reassociating_reduction_p): Return
	operands in canonical order.
	* tree-vectorizer.c (vec_info::new_stmt_vec_info): Initialize
	STMT_VINFO_REDUC_IDX.
	* tree-vectorizer.h (_stmt_vec_info::reduc_idx): New.
	(STMT_VINFO_REDUC_IDX): Likewise.

From-SVN: r275996