[30/77] Use scalar_int_mode for doubleword splits

[30/77] Use scalar_int_mode for doubleword splits

This patch uses is_a <scalar_int_mode> in a couple of places that
were splitting doubleword integer operations into word_mode
operations.  It also uses scalar_int_mode in the expand_expr_real_2
handling of doubleword shifts.

2017-08-30  Richard Sandiford  <richard.sandiford@linaro.org>
	    Alan Hayward  <alan.hayward@arm.com>
	    David Sherwood  <david.sherwood@arm.com>

gcc/
	* expr.c (expand_expr_real_2): Use scalar_int_mode for the
	double-word mode.
	* lower-subreg.c (resolve_shift_zext): Use is_a <scalar_int_mode>.
	* optabs.c (expand_unop): Likewise.

Co-Authored-By: Alan Hayward <alan.hayward@arm.com>
Co-Authored-By: David Sherwood <david.sherwood@arm.com>
From-SVN: r251482