reg-stack.c (propagate_stack): Always copy the source stack to the destination.

reg-stack.c (propagate_stack): Always copy the source stack to the destination.

	* reg-stack.c (propagate_stack): Always copy the source stack to
	the destination.  This routine is now only called when this is safe.
	(better_edge): New function split out from convert_regs_1 to
	determine which of two edges is better to propagate across.
	(convert_regs_1):  We need only search for a best edge if the
	stack layout hasn't been defined yet.  Use better_edge to help
	find beste.  No longer traverse unnecessary edges.

From-SVN: r100323