[04/11] Add a vect_orig_stmt helper function

[04/11] Add a vect_orig_stmt helper function

This patch just adds a helper function for going from a potential
pattern statement to the original scalar statement.

2018-08-01  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* tree-vectorizer.h (vect_orig_stmt): New function.
	* tree-vect-data-refs.c (vect_preserves_scalar_order_p): Use it.
	* tree-vect-loop.c (vect_model_reduction_cost): Likewise.
	(vect_create_epilog_for_reduction): Likewise.
	(vectorizable_live_operation): Likewise.
	* tree-vect-slp.c (vect_find_last_scalar_stmt_in_slp): Likewise.
	(vect_detect_hybrid_slp_stmts, vect_schedule_slp): Likewise.
	* tree-vect-stmts.c (vectorizable_call): Likewise.
	(vectorizable_simd_clone_call, vect_remove_stores): Likewise.

From-SVN: r263217