re PR middle-end/64391 (ICE: SIGSEGV in get_attrs_for (trans-mem.c:179) with -fgnu-tm and #pragma GCC ivdep)

	PR middle-end/64391
	* trans-mem.c (get_attrs_for): Return NULL_TREE if X is NULL_TREE.

	* gcc.dg/tm/pr64391.c: New test.

From-SVN: r219555