Simplify SLP code wrt SLP_TREE_DEF_TYPE

Simplify SLP code wrt SLP_TREE_DEF_TYPE

The following removes the ugly pushing of SLP_TREE_DEF_TYPE to
stmt_infos and instead makes sure to handle invariants fully
in vect_is_simple_use plus adjusting a few places I refrained
from touching when enforcing vector types for them.

It also simplifies building SLP nodes with all external operands
from scalars by not doing that in the parent but instead not
building those from the start.  That also gets rid of
vect_update_all_shared_vectypes.

2020-06-04  Richard Biener  <rguenther@suse.de>

	* tree-vect-slp.c (vect_update_all_shared_vectypes): Remove.
	(vect_build_slp_tree_2): Simplify building all external op
	nodes from scalars.
	(vect_slp_analyze_node_operations): Remove push/pop of
	STMT_VINFO_DEF_TYPE.
	(vect_schedule_slp_instance): Likewise.
	* tree-vect-stmts.c (ect_check_store_rhs): Pass in the
	stmt_info, use the vect_is_simple_use overload combining
	SLP and stmt_info analysis.
	(vect_is_simple_cond): Likewise.
	(vectorizable_store): Adjust.
	(vectorizable_condition): Likewise.
	(vect_is_simple_use): Fully handle invariant SLP nodes
	here.  Amend stmt_info operand extraction with COND_EXPR
	and masked stores.
	* tree-vect-loop.c (vectorizable_reduction): Deal with
	COND_EXPR representation ugliness.