[21/46] Make grouped_stores and reduction_chains use stmt_vec_infos

[21/46] Make grouped_stores and reduction_chains use stmt_vec_infos

This patch changes the SLP lists grouped_stores and reduction_chains
from auto_vec<gimple *> to auto_vec<stmt_vec_info>.  It was easier
to do them together due to the way vect_analyze_slp is structured.

2018-07-31  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	* tree-vectorizer.h (vec_info::grouped_stores): Change from
	an auto_vec<gimple *> to an auto_vec<stmt_vec_info>.
	(_loop_vec_info::reduction_chains): Likewise.
	* tree-vect-loop.c (vect_fixup_scalar_cycles_with_patterns): Update
	accordingly.
	* tree-vect-slp.c (vect_analyze_slp): Likewise.

From-SVN: r263136