gcc/:
	* lower-subreg.c: New file.
	* rtl.def (CONCATN): Define.
	* passes.c (init_optimization_passes): Add pass_lower_subreg and
	pass_lower_subreg2.
	* emit-rtl.c (update_reg_offset): New static function, broken out
	of gen_rtx_REG_offset.
	(gen_rtx_REG_offset): Call update_reg_offset.
	(gen_reg_rtx_offset): New function.
	* regclass.c: Revert patch of 2006-03-05, restoring
	reg_scan_update.
	(clear_reg_info_regno): New function.
	* dwarf2out.c (concatn_loc_descriptor): New static function.
	(loc_descriptor): Handle CONCATN.
	* common.opt (fsplit_wide_types): New option.
	* opts.c (decode_options): Set flag_split_wide_types when
	optimizing.
	* timevar.def (TV_LOWER_SUBREG): Define.
	* rtl.h (gen_reg_rtx_offset): Declare.
	(reg_scan_update): Declare.
	* regs.h (clear_reg_info_regno): Declare.
	* tree-pass.h (pass_lower_subreg): Declare.
	(pass_lower_subreg2): Declare.
	* doc/invoke.texi (Option Summary): List -fno-split-wide-types.
	(Optimize Options): Add -fsplit-wide-types to -O1 list.  Document
	-fsplit-wide-types.
	* doc/rtl.texi (Regs and Memory): Document concat and concatn.
	* Makefile.in (OBJS-common): Add lower-subreg.o.
	(lower-subreg.o): New target.
gcc/testsuite/:
	* gcc.dg/lower-subreg-1.c (test): New test.

From-SVN: r121453