Take register pressure into account for vec_construct/scalar_to_vec when the componen...

Take register pressure into account for vec_construct/scalar_to_vec when the components are not loaded from memory.

For vec_contruct, the components must be live at the same time if
they're not loaded from memory, when the number of those components
exceeds available registers, spill happens. Try to account that with a
rough estimation.
??? Ideally, we should have an overall estimation of register pressure
if we know the live range of all variables.

gcc/ChangeLog:

	* config/i386/i386.cc (ix86_vector_costs::add_stmt_cost):
	Count sse_reg/gpr_regs for components not loaded from memory.
	(ix86_vector_costs:ix86_vector_costs): New constructor.
	(ix86_vector_costs::m_num_gpr_needed[3]): New private memeber.
	(ix86_vector_costs::m_num_sse_needed[3]): Ditto.
	(ix86_vector_costs::finish_cost): Estimate overall register
	pressure cost.
	(ix86_vector_costs::ix86_vect_estimate_reg_pressure): New
	function.