[05/11] Add a vect_stmt_to_vectorize helper function

[05/11] Add a vect_stmt_to_vectorize helper function

This patch adds a helper that does the opposite of vect_orig_stmt:
go from the original scalar statement to the statement that should
actually be vectorised.

The use in the last two hunks of vectorizable_reduction are because
reduc_stmt_info (first hunk) and stmt_info (second hunk) are already
pattern statements if appropriate.

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

gcc/
	* tree-vectorizer.h (vect_stmt_to_vectorize): New function.
	* tree-vect-loop.c (vect_update_vf_for_slp): Use it.
	(vectorizable_reduction): Likewise.
	* tree-vect-slp.c (vect_analyze_slp_instance): Likewise.
	(vect_detect_hybrid_slp_stmts): Likewise.
	* tree-vect-stmts.c (vect_is_simple_use): Likewise.

From-SVN: r263219