expmed.c (choose_mult_variant, [...]): New, split from...

	* expmed.c (choose_mult_variant, expand_mult_const): New, split from...
	(expand_mult): ...here.
	(extract_high_half): New, split out from expand_mult_highpart.
	(expand_highpart_optab): Likewise.  Don't clobber target prematurely.
	(expand_highpart): Evaluate the cost of a shift/add sequence,
	then see if any of the specialized optabs are cheaper.

From-SVN: r79673