combine.c (combine_simplify_rtx): If nonzero_bits on op shows all bits zero in...

combine.c (combine_simplify_rtx): If nonzero_bits on op shows all bits zero in mode of a lowpart subreg, return zero.

	* combine.c (combine_simplify_rtx) <case SUBREG>: If nonzero_bits
	on op shows all bits zero in mode of a lowpart subreg, return zero.

From-SVN: r198595