re PR rtl-optimization/59461 (missed zero-extension elimination in the combiner)

re PR rtl-optimization/59461 (missed zero-extension elimination in the combiner)

	PR rtl-optimization/59461
	* doc/rtl.texi (paradoxical subregs): Add missing word.
	* combine.c (reg_nonzero_bits_for_combine): Do not discard results
	in modes with precision larger than that of last_set_mode.
	* rtlanal.c (nonzero_bits1) <SUBREG>: If WORD_REGISTER_OPERATIONS is
	set and LOAD_EXTEND_OP is appropriate, propagate results from inner
	REGs to paradoxical SUBREGs.
	(num_sign_bit_copies1) <SUBREG>: Likewise.  Check that the mode is not
	larger than a word before invoking LOAD_EXTEND_OP on it.

From-SVN: r242326