More efficient version of Jul 10 bugfix of mine, as

More efficient version of Jul 10 bugfix of mine, as
discussed on egcs-patches.
	* regclass.c (reg_scan_mark_refs): New arg min_regno.  Only update
	regscan information for REGs with numbers greater than or equal to
	this.  All callers changed.
	(reg_scan_update): New function to efficiently update regscan
	information on the fly.
	* rtl.h: Add prototype.
	* jump.c (jump_optimize): Call it when we make a transformation
	which generates new pseudo-REGs.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@21096 138bc75d-0d04-0410-961f-82ee72b054a4