Revert update-ssa assert in vectorizer

The following reverts the just added assert that virtual SSA does not
need updating.  It instead goes for a select whitelist of transforms
known to be prone to difficulties with virtual SSA update.

	* tree-vect-loop-manip.cc (vect_do_peeling): Revert assert
	and update virtual SSA form again.  Assert we do so for
	a known set of transforms only.
	* tree-vectorizer.h (vec_info::any_known_not_updated_vssa): New.
	* tree-vect-stmts.cc (vectorizable_load): When vectorizing
	using load-lanes allow virtual SSA update.
3 files changed