Revert:

	* fold-const.c (operand_equal_p): Remove code to allow null ARG0/1.
	Define locals macros OP_SAME and OP_SAME_WITH_NULL and use throughout.


git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@87089 138bc75d-0d04-0410-961f-82ee72b054a4