* simplify_rtx.c (simplify_subreg): Keep subregs on return values,
	check CLASS_CANNOT_CHANGE_MODE before avoiding subreg on hard reg,
	in case register wasn't OK previously, accept it now; allow
	subregs of frame pointer if reload completed and frame pointer
	is not needed.

	* combine.c (sombine_simplify_rtx): Fix comment;
	use subreg_lowpart_offset instead of subreg_lowpart_p
	(gen_lowpart_for_combine): Use subreg_lowpart_offset.
	* rtl.h (subreg_lowpart_parts_p): Kill.
	(subreg_lowpart_offset, subreg_highpart_offset): Declare.
	* simplify-rtx.c (simplify_subreg): Use subreg_lowpart_offset.
	* emit-rtl.c (gen_lowpart_SUBREG): Use subreg_lowpart_offset;
	(gen_lowpart_common): Likewise.
	(subreg_lowpart_p): Likewise.
	(subreg_lowpart_parts_p): Kill.
	(subreg_lowpart_offset, subreg_highpart_offset): New function.

	* emit-rtl.c (gen_lowpart_common): Use simplify_gen_subreg
	to simplify SUBREG and REG.
	(gen_highpart): Use simplify_gen_subreg for all simplifications.

	* emit-rtl.c (gen_realpart, gen_imagpart): Do not handle
	CONCAT specially.

	* rtlanal.c (replace_regs):  Use simplify_gen_subreg

From-SVN: r42850